CELLULAR FUNCTION

Fluid Compartments

Body weight: 18% protein, 7% mineral, 15% fat, 60% waterWater ingested (2100ml/day), synthesized via oxidation of carbohydrates (200ml/day)700ml/day lost through insensible losses (300-400 from resp tract, 300-400 from skin); 100ml/day lost through sweating, 100ml/day in poo42LDecreases with age (indirectly proportion to fat), women have less water than men

Extracellular Fluid Intracellular Fluid14L 28L

20% body weight 40% body weight1/3 TBW 2/3 TBW

High in Na, Cl, HCO3, Ca High in K, Mg, proteins, PO, organic anionsLow in protein High in protein (4x more)

A) Extracellular fluid: Difficult to measure as few substances stay truly extracellular and takes a long time to equilibrate in jt spaces, aqueous humour, CT, cartilage, CSFCannot be separated from lymph (returns protein back to the circulation

Interstitial fluid Blood plasma10.5L 3.5L

75% of ECF 25% of ECFOutwith vascular system In vascular system

Lower protein Higher proteinLower cations, higher anions Higher cations, lower anions

15% body weight 5% body weight

1) Interstitial fluid Can’t be measured directly as difficult to sample fluid and drugs will spread to plasmaECF/intracellular vol ratio is higher in children, so dehydration develops more rapidly in childrenInterstital vol = ECF vol – plasma vol

2) Blood plasma Total blood volume (5L, 7-8% body weight) = 60% plasma + 40% cellsHaematocrit (approx 0.36-0.4) = % of blood vol made up of cells

Plasma and interstitial fluid are constant mixing EXCEPT proteins which has a higher concentration in plasma as they can’t pass through capillary membrane, same ionic composition; because of Donnan effect conc of cations (+) is higher in plasma than interstitial fluid as protein is (-) binds cations, anions (-) higher in interstitial fluid

Total blood vol = plasma vol X (100 / 100 – haematocrit)Red cell volume = total blood vol – plasma vol

Glandular secretions, synovial, peritoneal, pericardial, eye, and CSF are separate from rest ECF so are transcellular fluids, small vol (1-2L) – these are in potential spaces; have very permeable membranes with free exchange of fluid with interstitial fluid/capillaries

B) Intracellular fluid:

Intracellular fluid28L40% body weight2/3 TBWHigh in K, Mg, PO, organic anions, proteinDecreases with age and women (indirectly proportional to fat)

Can’t be measured directly: ICF vol = TBW – ECF vol

Measuring Volume of Fluid CompartmentsMeasure vol of comptmt by injecting substance that will stay in that comptmt and calculating its dilutionMust be amount injected / metabolized must be accurately measured

non-toxicmix evenly through comptmt and not move to another comptmthave no effect on distribution of fluids in body

Vol of distribution (eg. Sucrose space) = amount of drug injected – amount excreted or metabolized in mixing period / conc of injected drug (remember: vol of drug x conc of drug in solution = mass of drug)

To measure TBW: deuterium oxide, tritium oxide, aminopyrine/antipyrine ECF vol: inulin, mannitol, sucrose, 22Na, 125I-iothalamate, thiosulfate, radioactive Cl Interstitial fluid vol: can’t be measured directly Plasma vol: Evans blue, 125I-albumin (labeled with iodine) Blood vol: RBC’s labeled with 51Cr, 59Fe, 32P or antigens ICF vol: can’t be measured directly

Measuring SolutesMole: molecular weight of substance in grams (eg. NaCl = 23 + 35.5g = 58.5g); 1 mole contains 6 x 1023 moleculesMillimole: 1/1000 of mole Micromole: 1/1,000,000 of moleMolecular weight (in Daltons): mass of 1 molecule of substance : mass of 1/12 mass of atom of C-12The Dalton: 1 Dalton = mass of 1/12 atom of C-12Kilodalton: 1000th of Dalton, expressed as K, used as measure of mass of proteins

Equivalent: 1 eq = 1 mol of ionized substance / its valence (eg. NaCl divides into 1 eq Na and 1 eq Cl 1 eq Na = 23g, 1 eq Ca = 40g/2)

pHIs negative logarithm of [H]; for each unit pH drops, [H] increased x10pH of water is 7.0 ([H] = 10-7)Need to maintain stable H; opposed by OH; should be 7.40Maintained by buffering capacity – buffer can bind/release H (eg. Carbonic acid H2CO3 = H + HCO3 – if H added, equilibrium shifts to L, if OH added it will bind to H taking it out of the system and H2CO3

dissociates shifting eq to R; blood proteins)

Movement Across Cell Membranes

1) DiffusionGas/substance expands to fill all available volume - net flux from area of high concentration to low conc 2Y to continual random movement of substances

Time taken to equilibrium α square of diffusion distanceMagnitude of diffusing tendency α area diffusion taking place over (eg. Number of channels)

conc gradient (diff in conc / thickness of boundary = Fick’s law of diffusion) (ie. Amount of substance) elec gradient (Nernst potential) – remember elec and conc gradients work together using Nernst equation pressure difference across membrane (the sum of all forces of molecules striking unit surface area) velocity of kinetic motion

a) Simple diffusion: no interaction with carrier proteins; just through membrane/channelb) Facilitated diffusion: involves interaction with carrier protein, including binding and

conformational change but needs no energy; in simple diffusion rate of diffusion is α to conc gradient, in facilitated there is a max diffusion rate (ie. It plateaus)

Non-polar/lipid-soluble molecules (eg. O2, N2, CO2) can diffuse directly across lipid membranes of cells, but membranes have limited permeability to others therefore diffusion occurs through channels.Filtration: occurs in capillaries; process by which fluid forced through a membrane due to difference in pressure on 2 sides; plasma proteins/colloids can’t pass through unless by vesicular transport osmotic pressure named oncotic pressure which opposes filtration out of capillaries

2) OsmosisThe net diffusion of water across a selectively permeable membrane from a region of high water conc to low water conc

High osmolality = concentrated solution = high osmotic pressureCell membranes are relatively impermeable to solutes

3) Intercellular Connectionsa) Tight Junctions (zonula occludens): tie cells together, strength and stability (eg. In intestine, renal

tubules, choroid plexus); interlocking ridges; permits passage of some ions and solute, prevent the movement of protein, maintaining different distribution of transporters in apical / basolateral membranes

b) Gap Junctions: narrow intercellular space (3nm as opposed to 25nm) at this point; units called connexons (made up of 6 connexins surrounding a channel 2nm wide) that connects to connexon in adjacent cell passage of substances (eg. Molecular weight <1000 – ions, sugars, aa’s) without entering ECF; permit rapid propogation of electrical current; Charcot-Marie-Tooth disease is 2Y to mutation of connexin

4) ExocytosisVesicles bond to cell membrane via v-SNARE/t-SNARE arrangement area of fusion breaks down. Ca dependent; results in addition to cell membrane 2 pathways: non-constitutive: proteins enter secretory granules processing from pro-hormones to

hormones exocytosis constitutive pathway: pro-hormones released before processed

5) EndocytosisPhagocytosis: bacteria, dead tissue etc… binds with receptor membrane invaginates outwards to engulf bacteria more receptor bind to bacteria phagocytic vesicle formed actin and other fibrilar proteins contact forcing vesicle into cell and pinch it off (eg. Macrophages, WBC). If bacteria is tagged by ab this is opsonisation. Pinocytosis: same as phagocytosis, but substances ingested in soln, not visible under microscope; the only means by which macromolecules can enter cellsResults in removal from cell membrane

Can be constitutive: not specialized clathrin-mediated: receptor found at coated pits under which is latticework of fibrillar protein

clathrin accumulated pit invaginates inwards clathrin surrounds endocytic vesiscle protein at neck of vesicle named dynamin involved in pinching off vesicle clathrin falls off

pinocytic vesicle fuses with endosome and dumps contents into early endosome becomes late endosome which fuses with lysosome contents digested by proteases in lysosome; responsible for internalization of any receptors and ligands (eg. Nerve GF, LDL), role in synaptic function; requires intracellular ATP and extracellular Ca to aid in pinching of vesicle

Lysosomes: large irregular structures surrounded by membrane formed by breaking off from GA; acidic interior helps in phagocytosis to digest food/damaged structures (lysosomes burst and digest damanged part of cell, or cause autolysis if cell badly damaged)/bacteria; will attach to vesicles that has been endocytosed empty hydrolases into vesicles digestive vesicle once digestion over, residual body composed of indigestible substances excreted by exocytosis; if lysosomal enzyme is absent lysosomal storage disease; contain hydrolase enzymes which split matter by adding H to one part and OH to another (eg. Glycogen glu, proteins aa) (eg. ribonuclease, deoxyribonuclease, phosphatase, glycosidases, collagenase); for killing bacteria it uses lysozyme (for bacterial membrane), lysoferrin (for Fe) and acid (to activate hydrolases and inactivate metabolism of bacteria)

NB. All vesicles involved in 4) and 5) have protein coats; certain aa sequences on coats can ticket vesicle to travel to certain areaNB. When a combination of 4) and 5) used to take things out of capillaries this is transcytosis/vesicular transport

6) Ion ChannelsAre channels; may be selectively permeableMay be a) constantly open b) gated - By voltage (eg. Na channel gate opens when inner membrane loses its (-) charge; K

channel gate opens when inside cell becomes (+) charged) All-or-none – channel is either opened or closed rapidly at certain voltages

By ligands (eg. Ach channel) – binding of ligand caused conformational changeExternal ligands (eg. Neurotransmitter, hormone)Internal ligands (eg. Ca, cAMP, G proteins)

By mechanical stretch

6) CarriersBind molecule and change its configuration when moving it

a) Facilitated diffusion: if moving in direction of conc/elec gradient, need no energy (eg. Glu, aa)b) Active transport: against gradient; uses ATP therefore carriers are ATPases (eg. Na-K ATPase, H-

K ATPases in gastric mucosa and renal tubules, Ca ATPase)c) Secondary active transport: Na transport coupled with other substances as co-transport or

countertransport (eg. Na with Glu in intestine, Na with aa; Na against Ca in heart muscle, Na against H in PCT); if Na is diffusing along a conc gradient, it’s excess energy can take another substance with it

Types are: Uniports: transport only 1 substance Symports: transport >1 substance together (eg. Na and glu from intestinal lumen into mucosal

cells) Antiports: exchange one substance for another (eg. Ca out, Na in in cardiac muscles)

NB. Patch clamping used to investigated transport proteins. Can be cell-attached / inside-out patch, or whole cell recording.

NB. Sometimes substances must pass through ‘cellular sheets’ using combination of transport.

Prinicples of Osmosis

Osmotic pressure: pressure necessary to prevent solute migration (α to no. particles in certain vol of soln) higher osmotic pressure = higher solute concentration related to temp and vol

dependent upon number rather than type of molecules 1mosm/L exerts 19.3mmHg of osmotic pressure so normal osmotic pressure of body fluids is 19.3 x 300 = 5790mmHg (5500 since not an ideal soln)

Osmoles: express the conc of osmotically active particles 1 osmole = weight of substance / no. freely moving particles each molecule liberates in soln

= 1 mole of solute particles = 1 gram molecular weight of osmotically active soluteIons will partially dissociate to become separate osmoles 1mol of NaCl osmolar conc of 2osm/L 1 molecule of albumin exerts same effect as 1 molecule glucose Osmole refers to NUMBER of osmotically active particles, not the molar concentration nor the weight of the particle – all particles will exert roughly same amount of pressure on membrane as small molecules move fast and large slow same kinetic energy Ionic interactions prevent soln from being ideal soln and decrease its osmotic pressure Use the osmotic co-efficient of a substance in calculations to allow for this The more concentrated the solution the less it is an ideal soln

Osmolal conc: measured by extent to which it decreases freezing point of soln 1 mol of ideal soln decreases freezing point by 1.86˚C expressed as osm/L of water

Osmolarity: no. osmoles per litre soln affected by vol of solutes in soln and by temp

Osmolality: no osmoles per kg solvent; Soln that has 1 osmole solute dissolved in kg water has osmolality of 1 osmole per kg

NOT affected by vol of solute / temp Interstitial fluid and plasma: is 2Y to Na and Cl Intracellular fluid: is 2Y to K Plasma: Na, Cl, HCO3, plasma proteins, glucose, urea Plasma has slightly higher osmolarity than ISF and ICF 2Y to plasma proteins; but all approx 300mOsm/L

Plasma osmolality = 2[Na] + [Glu x 0.055] + [BUN x 0.36]If plasma osmolality > than formula expects, likely foreign substance (eg. Ethanol, mannitol)

Tonicity: osmolality of soln relative to plasma (eg. Isotonic, hypertonic) cells can swell/shrink when exposed to changed tonicity so long as solute can’t permeate membrane Ion channels help maintain isotonicity (eg. Efflux of K + Cl if cell swells water follows) N saline remains isotonic (mostly Na, Cl, HCO3) increased ECF vol, no movement of water 5% glu is initially isotonic but glu is metabolised to becomes hypotonic 0.45% NaCl is hypotonic water moves into cells increase ICF and ECF volHypertonic water moves out of cell increase ECF vol, decrease ICF vol, increase osmolarity both compartments

Resting Membrane Potential

Non-ionic diffusion: when undissociated substance diffuses across membrane then dissociates therefore can’t cross membrane net movement in one direction (eg. In GI tract, kidneys)

Donnan effect: when an ion (eg. Prot-) can’t diffuse across membrane, affects diffusion of other ionsThe diffusible ions distribute so concn ratios are equal

Gibbs-Donnan equation : (Ka/Kb = Clb/Cla) or (Ka x Cla = Kb x Clb)

Intracellular protein concn is higher more osmotically active particles intracellularily than in interstitial fluid cells would swell and rupture if not for Na-K ATPase. Since plasma protein > interstitial fluid protein similar situation at capillary walls Concn of ions on either side of membrane is assymetrical electrical difference across membrane which is exactly balanced by chemical gradient

eg. Chloride ions: 1) Cl conc higher in ECF than intracellular Cl diffuse INTO cell along concentration gradient2) Intracellular charge (-) compared to extracellular Cl diffuse OUT along electrical gradient3) Equilibrium established: efflux = influx membrane potential here is equilibrium potential of Cl

(magnitute calculated by Nernst equation – the diffusion potential across membrane that is needed to prevent net diffusion of an ion, determined by ratio of conc of ion on either side of membrane)

a. Potential dependent upon electrical charge of ions, permeability of membrane, conc of ions on either side

b. Ion can only be involved in potential if membrane is permeable to itc. At equilibrium there is excess cations (+) outside, excess anions (-) inside

Ion Conc in cell Conc outside cell Equilibrium potential Conc Grad Elec GradNa 15 150 +60 (+ ion coming in) IN INK 150 5.5 -90 (+ ion going out) OUT INCl 9 125 -70 (- ion coming in) IN OUT

Resting membrane potential is -70mV = ECl. Neither ENa or EK is at RMP you expect cell to gradually gain Na and lose K water to enter cell due to large Na in cell cell to burst. Prevented by Na-K ATPase (2K in, 3Na out) working against chemical and electrical gradients to maintain RMP. NA-K ATPase MAINTAINS MEMBRANE POTENTIAL.

Na-K ATPaseElectrogenic pump: catalyses hydrolysis of ATP ADP 3Na out, 2K in for each molecule ATP. Hence internal of cell remains (-) compared to exterior.

Extends through cell membrane Vital in controlling volume of cell Inhibited by ouabain and digitalis; separation of subunits eliminates action Accounts for 24% energy used by cells, 70% in neurons Pump is not saturated at normal conditions Activity affected by 2nd messengers (eg. cAMP, diacylglycerol); increased by thyroid, insulin and

aldosterone (increase number of Na-K ATPase molecules); inhibited by dopamine (phosphorylates it)

Heterodimer: α subunit – spans membrane 10x; molecular weight 100,000

Na + K transport occurs through this Binding sites: intracellular - 3 Na and 1 ATP binding sites and phosphorylation site Extracellular – 2 K and ouabain

Na binds intracellularily, K binds extracellularily ATP binds phosphate transferred to phosphorylation site change in configuration Na transferred out, K inCan work in reverse with phosphorylated site donating P to ADP

α1 – found in all cells α2 – found in muscle, heart, adipose tissue, brain α3 – found in heart and brain

β subunit – spans membrane once; molecular weight 55,000; may act as an anchor

a glycoprotein with 3 extracellular glycosylation sites

β1 – absent in astrocytes, vestibular cells, fast-twitch muscle β2 – found in fast-twitch muscle β3

NB. There is a K-Na leak channel which allows K>Na leakage through which the initial equilibrium of ions is made to form RMP therefore K most important in determination of RMP.

Specific Ion Channels

1) K channels: Tetramers (4 subunits with a charged extension which surround a pore) When closed positive extensions are near negatively charged interior of cell membrane

potential decreased paddles bend towards outside channel opens Channel has small diameter therefore selective for small K, Na can’t pass through

2) Ach channel and many other anion/cation channels: 5 subunits3) Cl channel: many different types

Dimer (2 subunits), but with a pore in each subunit Pentamers (5 subunits) (eg. GABA and glycine receptors)

4) Aquaporins: tetramers with water pore in each subunit; note, water can also travel by simple diffusion5) Ca channel: many different types. Ca v low intracellularly as 1 pump pumps Ca into ECF, and another pumps Ca into vesicular organelles (eg. SR, mitochondria)6) H channel: in parietal cells of gastric glands and intercalated cells of DCT and CD of kidneys

6) Na channel: many different types Can be blocked by tetrodotoxin and saxitoxin therefore can be tagged and investigated Inner surface is (-) to attract (+) Na ions Certain type = Epithelial sodium channels

In kidneys, colon, lungs, brainHave 3 subunits: α: transports Na (inhibited by amiloride which binds it)

β and γ: aid transportSpan membrane twicePlay role in ECF vol via aldosterone

Intercellular Communication

Messengers: (eg. Amino acids, steroids, polypeptides, lipids, nucleotides) can be measured by making ab’s and using radioimmunoassay – competes with endogenous ligand for receptor

Neural communication: NT’s released at synaptic junctions; local response Endocrine communication: hormones and GF’s by circulating in body fluid; general response Paracrine communication: diffuse to neighbouring cells in interstitial fluid; locally diffuse

response Autocrine communication: messengers bind to own cell Juxtacrine communication: cells express GF’s (eg. Transforming GF α) extracellularily on

transmembrane proteins, whereas other cells have TGF receptors 2 cells can bind

Also: Gap junctions: direct from cell to cell; local response

Receptors are active not staticDown-regulation occurs if XS of hormone/NT is present (eg. Via receptor-mediated endocytosis,

ligand-receptor complex is internalized; in desensitization receptors are chemically altered on binding)

Up-regulation in deficiency

First messengers: extracellular ligandsOften work via GTP-binding proteinsCan cause release of second messenger (intracellular ligands)

Bring about short term changes in cells Can activate transcription factors induce transcription of immediate-early genes

alter transcription of genes to produce products that cause longterm changes Often activate protein kinases catalyse phosphorylation of tyrosine/serine/threonine

change of configuration alter function Intracellular part of receptor may be protein kinase (eg. Insulin)Phosphatases vital here

Eg. Of Protein Kinases

Phosphorylate serine and/or threonine residues

Calmodulin-dependent Myosin light-chain kinasePhosphorylase kinaseCa/calmodulin kinase I, II, III

Ca-phospholipid dependent Protein kinase CCyclic nucleotide dependent cAMP-dependent kinase (protein kinase A)

cGMP-dependent kinasePhosphorylate tyrosine residues

Insulin receptorEGF receptorPDGF receptorM-CSF receptor

Effects of Messengers

1) Open/close ion channels Change conductance

eg. Ach on nicotinic cholingergic receptor, noradrenaline on K channel in heart

2) Increase transcription of mRNA’s via cytoplasmic/nuclear receptors Activated receptor has DNA-binding portion which is usually covered by heat shock protein (Hsp90, amount increases in times of stress) Hsp90 release receptor-ligand complex binds to untranslated 5’-flanking portions of genes increased transcription of mRNA’s increase proteinsLigand-binding portion of receptor is near carboxyl terminal

eg. Thyroid – receptor in nucleus Steroid – receptor in nucleus for oestrogen, in cytoplasm for glucocorticoid; steroids also

have nongenomic actions via 2nd messengers which have faster action 1,25-dihydroxycholecalciferol, retinoids

3) Activate phospholipase C with intracellular production of DAG and IP3 Ligand binds receptor activation of phospholipase C on inner membrane via Gq protein or tyrosine kinase link catalyse hydrolysis of PIP2 (phosphatidylinositol 4,5-diphosphate) into IP3 (inositol 1,4,5-triphosphate) and DAG (diacylglycerol) IP3 triggers release of Ca from ER, DAG activates protein kinase C in cell membrane

eg. Angiotensin II, noradrenaline via α1-adrenergic receptor, vasopressin via V1 receptor

4) Activate/inhibit adenylyl cyclase inc/dec production cAMP (cyclic adenosine 3’,5’- monophosphate)Adenyly cyclase: catalyst; transmembrane protein crossing membrane 12x

Activated by Gs α subunit when stimulatory receptor bound cAMP formed from ATP activates protein kinase A catalyses phosphorylation of proteins including CREB (cAMP-responsive element-binding protein) altered

activity and transcription of genesDeactivated by Gi α subunit when inhibitory receptor bound

Phosphodiesterase converts cAMP to inactive 5’-AMP (inhibited by caffeine and theophylline)eg. Noradrenaline via α2 adrenergic receptor dec cAMP Noradrenaline via β1-adrenergic receptor inc cAMP Cholera toxin inhibits GTPase activity, prolonging stimulation of adenylyl cyclase Pertussis toxin inhibits function of Gi

5) Increase cGMP (cyclic guanosine monophosphate) in cell cGMP important in vision, helps regular ion channels

Guanylyl cyclase: catalyses formation of cGMP; 2 forms: Transmembrane form: has extracellular, transmembrane and cytoplasmic portion (eg. Receptor for ANP, receptor for E. coli enterotoxin)Intracellular form: soluble, containing heme (eg. Activated by NO)

6) Increase tyrosine kinase activity of transmembrane receptors Tyrosine kinases are closed associated with phosphatases, to remove phosphate groups from proteinseg. Insulin, EGF, PDGF, M-CSF

7) Increase serine/threonine kinase activity eg. TGF, MAPKs

G ProteinsBind GDP/GTPGTPase activity encouraged by RGS (regulators of G protein signaling) proteinsMany G proteins are lipidated

a) Small G proteins: eg. Rab (regulate vesicle traffic) Rho/Rac (regulates interactions between cytoskeleton and cell membrane) Ras (regulates growth)

b) Heterotrimeric G proteins: Couple receptors to catalysts for formation of 2nd messengers / ion channels 5 families (Gs, Gi, Gt, Gq, G13) Receptors coupled with G protein usually span cell membrane 7 times (serpentine receptors)

o G proteins interact with aa residues in 3rd cytoplasmic loop of receptoro Small ligands bind to amino acid residues in membraneo Large protein ligands bind to extracellular domains of receptor

Made of α, β and γ subunitso α bound to GDP ligand binds to G-coupled receptor GDP exchanged to GTP α

separated from β and γ effect via α and βγ complexes (eg. Ion channels, enzymes) brought about GTPase activity of α converts GTP to GDP reassociation of all units termination of effect

Ligands for receptors coupled to heterotrimeric G proteins

Neurotransmitters Epinephrine, norepinephrine, dopamine, 5-hydroytryptamine, histamine, Ach, adenosine, opioidsTachykinins Substance P, neurokinin A, neuropeptide KOther peptides Angiotensin II, arginine vasopressin, oytocin, VIP, GRP, TRH, PTHGlycoprotein hormones TSH, FSH, LH, hCGArachidonic acid derivatives Thrombozane A2Other Odorants, tastants, endothelins, PAF, cannabinoids, light

Intracellular CaAt rest 100nmol/L

Multiple effects of Ca: changes may outlast high concentration of Ca intracellular; conc may oscillate; raised conc can spread from cell to cell in waves co-ordinated response

Extracellular: high concentration; chemical and electrical gradient inwardsIntracellular: Ca bound by ER and other organelles acting as a store

Intracellular Ca activated by 2nd messengers (eg. Release from ER and mitochondria mainly caused by IP3) may cause store-operated Ca channels in membrane to open Ca influx free Ca activates Ca-binding proteins activate protein kinases; free Ca also replenishes ER storesCa-binding proteins eg. Troponin in contraction of skeletal muscle

eg. Calmodulin which activates 5 different calmodulin-dependent kinases eg.a) myosin light-chain kinase phosphorylates myosin contraction of smooth muscleb) phosphorylase kinase activates phosphorylase; role in synaptic function and protein synthesisc) calcineurin inactivates Ca channels by dephosphorylating them; activates T cells, inhibited by immunosuppressants

eg. Calbindin

Enters cell: through ligand gated channels stretch gated channels voltage gated channels (T transient or L longacting depending on whether deactivate during prolonged depolarisation)

Exits cell: by Ca-H ATPase (2H in, 1Ca out) antiport (3Na in, 1Ca out) – driven by Na gradient

Ca sparks is site of high concentration of Ca where it leaves cell

Growth FactorsActivate transcription factors which move to nucleus and alter gene transcription4 main groups:

1) Agents which foster multiplication/development of various cells (eg. Nerve GF, ILGF, activins, inhibins, epidermal GF)

2) Cytokines – produced by macrophages and lymphocytes; regulate immune system3) Colony stimulating factors – regulate proliferation and maturation of RBC and WBC’s4) TGFβ and related polypeptides – receptors have serine-threonine kinase activity; effects mediated

by SMAD’s bind DNA to initiate transcription of genes

In 1) receptor has membrane-spanning domain and intracellular tyrosine kinase domainLigand binds tyrosine kinase domain autophosphorylates transcription factors and altered gene expression

In 2) and 3) most receptors don’t have tyrosine kinase domains, but use JAK-STAT pathway Ligand binds transmembrane protein gp130 initiate tyrosine kinase activity in cytoplasm (eg. JAKS (Janus tyrosine kinases)) phosphorylation of STAT (signal transducer and activator of transcription) proteins act as transcription factors at nucleus.

Diseases

Site Type of Mutation DiseaseReceptor

Cone opsins Loss Color blindnessRhodopsin Loss Congenital night blindnessV2 vasopressin Loss Nephrogenic diabetes insipidisACTH Loss Glucocorticoid deficiencyTSH Loss HypothyroidismThromboxane A2 Loss Congenital bleedingEndothelin B Loss Hirschsprung diseaseLH Gain Male precocious pubertyTSH Gain Nonautoimmune hyperthyroidism

Ca Gain Hypercalciuric hypocalcaemiaG protein

Gs α Loss PseudohypothyroidismGs α Gain Testotoxicosis

McCune-Albright SyndromeGi α Gain Ovarian and adrenocortical tumours

Grave’s disease: ab against TSH receptorMyaesthenia gravis: ab against nicotinic Ach receptors

NERVES

Nervous tissue made of neurons and glial cells

Nerve Cells

Dendrites: 5-7; extend from cell body; have knobbly projections called dendritic spines esp in brain; cell body may be at dendritic end, but may be anywhere within axon (eg. Auditory neurons) or to side of axon (eg. Cut neurons)Axon: fibrous; poor passive conductor, conduction is active

originates from axon hillock on cell body1st part is initial segmentterminal branches end in synaptic knobs (terminal buttons, axon telodendria) which contain granules containing NT’smyelinated (protein-lipid complex wrapped around axon, no myelin at nodes of Ranvier)

produced by Schwann cells outside of brain which wrap membrane around 1 axon that it sits on protein 0 (P0) locks to P0 of opposing membrane to compact myelin down) produced by oligodendrogliocytes in CNS – send off multiple processes that form myelin on neighbouring axons

unmyelinated (surrounded by Schwann cells but no wrapping)Epineurium: peripheral nerves made of multiple axons in fibrous envelope

4 important regions:1) Receptor/dendritic zone: changes producted by synaptic connections are integrated2) Site where AP’s are created: initial segment in spinal MN’s, initial node of Ranvier in cut SN’s3) Axonal process: transmits impulses to nerve endings4) Nerve endings: AP’s cause release of NT’s

Protein synthesis: occurs in cell body transported to axonal ending by axoplasmic flow; in some cases mRNA strands are transported from cell body to ribosomes and protein synthesis occurs locally

Anterograde transport: along microtubules (fast at 400mm/d, slow at 5-10mm/d)Retrograde transport: along microtubules (200mm/d); some used synaptic vesicles and substances taken up by endocytosis (eg. Nerve GF) may be transported back to cell body

If axon cut, distal parts degenerated (Wallerian degeneration)

Excitation and Conduction

Measure electrical events with cathode ray oscilloscope – uses cathode which shoots electrons at glass tube coated with phosphors, +ive and –ive charged plate applied on either side of course of beam, when voltage applied across it beam pulled towards +ive plate, measure course of beam to work out voltage

May result in:Local, nonpropogated potentials: synaptic/generator/electronic potentialsPropogated potentials: action potentials

Excitation

Low thresholdResting membrane potential of nerve cells is -70mV (inside cell –ive compared to outside)

Stimulus may be electrical, chemical, mechanicalMinimal intensity of stimulating current that acting at given duration will cause AP is threshold intensity – with weak stimuli this is long duration, with strong may be short strength-duration curveSlowly rising currents fail to cause AP due to accommodationOnce threshold intensity reaches, AP will fire; increase in stimulation won’t cause increased AP – all-or-none lawSubthreshold stimuli will still have effect on membrane potential via local response even if don’t cause AP – electronic potentials (if produced by cathode – catelectronic, if anode – anelectronic); potential is proportionate to current

These will affect threshold – catelectronic are depolarizing lower threshold Anelectronic are hyperpolarizing incr threshold

When stimulus applied stimulus artifact recorded by CRO due to current leakage from stimulating to recording electrodesFollowed by latent period – ends with start of AP; = time it takes impulse to travel along axon from site of stimulation to recording electrodes; duration proportionate to distance between stimulating and recording electrodes, inversely proportionate to speed of conduction – if you know distance you can work out speed of conductionIn peripheral nerves with multiple axons in epineurium some axons may be conducting and others not; stimulus that produces excitation of all axons is maximal stimulus

Action potentials due to changes in conduction of ions across membraneAfter 15mV depolarization, rate of depolarization increases – this is firing level/thresholdPotential overshoots isopotential to +35mVSpike potential occursRepolarisation – slows after 70% to perform after-depolarisationOvershoot slightly to form after-hyperpolarisation – this is a small amplitude but long duration; it will increase if nerve has been conducting for a long timeFollowed by refractory period

Absolute: time from firing level until repolarisation 1/3 complete; NO stimulus will excite nerve

Relative: from 1/3 complete til start of after-depolarisation; stronger stimuli can exciteDuring after-de and after-hyperpolarisation threshold is increased

Peripheral nerves will produce compound AP as there will be some fast and some slow conducting axons, some cell bodies may be further away

Ionic basis: remember Na diffuses in (along elec and conc grad) K diffuses out (along conc grad only) Na actively transported out K actively transported in

Greater permeability to K so K determines resting membrane potential

When stimulus applied voltage-activated Na channels activated NA INFLUX firing level met Na effect overwhelms K effect for short time depolarization membrane potential moves towards +60mV spike potential doesn’t reach +60mV as Na channels only activated for short time Na channels close and Na influx prevented by membrane potential voltage-gated K channels open (longer time) K EFFLUX repolarisation followed by after-hyperpolarisation as K channels still open.

Decreasing extracellular [Na] decr AP, no effect on MP as Na not important thereIncreasing extracellular [K] decr RMPDecreasing extracellular [Ca] increases excitability as decr amount of depolarization needed to start changes in Na and K conductance

Accomodation: 2Y to slow opening of K channels; if Na channels stimulated over long time then K channels are still open so effect of Na channels decreased

ConductionOccurs along axons; is active not passive; impulse moves at constant amplitude and velocity At rest inside nerve is +ive, outside –ive (POLARISED) during AP polarity reversed, AP creates area of –ive charge and +ive charges from alongside (ahead and behind) move to this area – current sink decreases polarity of membrane ahead of AP local response until firing potential reached proprogated response.

Saltatory conduction: myelin is effective insulator; depolarization jumps from 1 node of Ranvier to next; myelinated conduction 50x faster than unmyelinated; Na channels concentrated in node and initial segment (where AP generated)If AP initiated in middle of axon, impulse can travel either way

Orthodromic: when impulses travel in 1 direction only; in mammalsAntidromic: when impulses travel in opposite direction; since synapses are unidirectional, this impulse will die when it reaches one

Biphasic AP: when you measure AP with 2 electrodes on inside of membrane; electrode 1 –ive 2 electrodes same electrode 2 –iveVolume conductor: conducting medium of body; complicates above processes somewhat

Nerve Fibre Types

Fibre Type

Function Diameter Conduction Velocity

Spike duration

Absolute refractory period

Aα Proprioception (Sensory to muscle

spindle (Ia) and golgi tendon organ (Ib)); somatic motor

12-20 (large) 70-120 (fast) 0.4-0.5 (short)

0.4-1 (short)

β Touch (II), pressure (II), motor 5-12 (mod) 30-70 (mod)γ Motor to muscle spindles 3-6 (small) 15-30 (mod)δ Pain, cold, touch (III) 2-5 (small) 12-30 (mod)B Preganglionic autonomic <3 (small) 3-15 (mod) 1.2 (long) 1.2 (long)C (IV)Dorsal root

Pain, temp, reflexes, mechanoreception 0.4-1.2 (small) 0.5 – 2 (slow) 2 (long) 2 (long)

Sym Postganglionic sympathetics 0.3-1.3 (small) 0.7 – 2.3 (slow)

2 (long) 2 (long)

Susceptible to… Very Intermediate LowHypoxia B A CPressure A B CLA C B A

I-IV used to describe sensory fibres as above

Neurotrophins

Produced by astrocytes/muscles1) Bind to receptors at end of neuron endocytosis retrograde transport in cell body cause production of proteins for neuronal growth and survival2) Produced in neurons anterograde transport to nerve ending support postsynaptic neuron

Bind to trk receptors dimerise autophosphorylation of tyrosine kinase domains of receptorseg. NGF trkA; brain-derived GF trkB; neurotrophin 3 trkC; neurotrophin 4+5 trkB

NGF: growth and maintenance of sym and sensory neurons; made up to 2 α (trypsin-like activity), 2 β (growth promoting activity) and 2 γ (serine proteases) subunits; work by process 1) described above; important in maintenance of cholinergic neurons in brain (ie. Sym nervous system)NT-3 – cutaneous mechanoreceptorsBDNF – peripheral senory neurons

Others: CNTF (ciliary neurotrophic factor) produced by Schwann cells and astrocytes – for survival of spinal cord neuronsGDNF (glial cell linee-derived NTF) for midbrain and dopaminergic neuronsLIF (leukemia inhibitory F), IGF – I, TGF, fibroblast GF, PDGF

Neuroglia

Microglia: like tissue macrophages; originate in bone marrowOligodendrogliocytes: for myelin formationAstrocytes: induce capillaries to form tight junctions for BBB; envelop synapses and surfaces of nerve cells; produces substances tropic to neurons; maintain appropriate conc of ions and NT’s by taking up K, glutamate and GABA

Fibrous – in white matterProtoplasmic – in gray matter

MUSCLE

Can be excited electically, chemically, mechanicallyCan be skeletal, cardiac, smooth

Skeletal Cardiac SmoothStriated? Yes Yes NoMitochondria Many FewMicroscopic features

T tubule contact at A-I band

Intercalated discs and gap junctions; T tubule contact at Z line

Dense bodies in cytoplasm

RMP -90 -90 -50Action potential

2-4ms long Prolonged plateau phase (200ms)

Sometimes prolonged plateau phase

Metabolism Slow / fast twitch Slow-twitch, low ATP-ase activity, oxidative metabolism, high in myoglobin

Dependent on glycolysis

Stimulation External needed Contains regular pacemaker; modified by external

Contains irregular pacemaker

Contraction Ca binds troponin C tropomyosin moves laterally myosin binds

Ca binds troponin C tropomyosin moves laterally myosin binds

Ca binds calmodulin calmodulin-dependent myosin light chain kinase activated catalyses phosphorylation of myosin light chain

Skeletal MuscleEach fibre is multinucleated, long, cylindricalSurrounded by membrane (sarcolemma) Each fibre made of myofibrils, made of thick and thin filamentsEach fibril surrounded by sarcotubular system

T tubules: continuous with sarcolemma; forms grid perforated by fibrils; space between 2 layers is continuous with extracellular; contact A+I bands twice each sarcomere; allows rapid transmission of AP from cell membrane to all fibrils in muscleSarcoplasmic reticulum: surrounds each myofibril; has enlarged terminal cisterns in close contact with T system at junctions between A+I bands at triads; involved in Ca movement and muscle metabolism

Dystrophin: large protein that connects actin (thin filament) to β-dystroglycan (protein in sarcolemma); β-dystroglycan attached by α-dystroglycan to laminin in extracellular matrix; sarcoglycans also involved; dystrophin-glycoprotein complex provides strength and scaffolding by connecting to extracellular enviro

Striations: due to diff refractive indexes of diff parts of muscle fibres; each thick filament surrounded by 6 thin filaments in hexagonal patter

I band: light, thin filamentThin filament: actin (300-400 molecules), tropomyosin (40-60 molecules) and troponin

Actin: 2 chainsthat form long double helixTropomyosin: located in groove between 2 actin molecules; covers site where myosin binds actinTroponin: globular units at intervals along tropomyosin molecules

Troponin T: binds troponin to tropomyosinTroponin I: inhibits interaction of myosin with actin by tightly binding actinTroponin C: contains binding sites for Ca to initiate contraction

A band: dark, thick filament; has lighter H band in centre (where actin and myosin don’t overlap when muscle relaxed); transverse M line in middle of H band (site of reversal of polarity of myosin molecules in thick filaments)

Thick filament: myosin II (700 molecules) (2 globular heads and long tail); heads of myosin form cross-links with actin at actin-binding site, hydrolyse ATP at catalytic site

Z line: sarcomere between 2 Z lines; transect fibrils and connected to thin filaments by actinin; connected to M line by titin (provides scaffolding – at beginning of stretching domains unfold so little resistance, but provides protection as stretch continues); Z line bound to plasma membrane by desmin

Contraction

In contraction: width of A band constant, distance between Z lines decreasesMyosin head binds actin ‘power-stroke’ needing hydrolysis of ATP shortening sarcomere by 10nm per powerstroke detach; each head cycles 5x/sec

Excitation-contraction coupling: discharge of motor neuron release of Ach at motor end plate Ach binds nicotinic receptors end plate potential AP AP transmitted to all fibrils by T tubules dihydropyridine receptors (voltage gated Ca channels) in T tubule membrane activated trigger release of Ca via ryanodine receptor in SR (ligand gated channel related to IP3) from terminal cisterns of SR Ca binds troponin C binding of trop I to actin weakened tropomyosin moves laterally uncovering binding sites for myosin myosin binds ATP split contraction.

Relaxation: Ca it is reabsorbed into ST by ATP-mediated active transport in Ca-Mg ATPase returns to terminal cisterns to be stored (if this can’t occur muscle can’t relax contracture) once Ca conc decreased by taking back up into SR, myosin and actin action ceases relax (ATP needed for contraction and relaxation).

Electrical Events

RMP = -90mVAP is 2-4ms longSpeed of AP is 5m/sAbsolute refractory period = 1-3msAfter-polarisations are longDistribution of ions across membrane similar to that in nerves (Na high extracellular, K high intracellular, CL high extracellular, HCO3 high extracellular)

Depolarisation occurs from NA INFLUX, repolarisation from K EFFLUX; begins at motor end plate, AP conduction results in contractile response; 1 AP results in muscle twitch beginning 2ms following depolaristationFast-twitch: fine, rapid, precise movement; 7.5ms twitch durationSlow-twitch: strong, gross, sustained movement; 100ms twitch duration

Principles of Contraction

Isometric contraction: when contraction occurs without change in length of muscle; do not do workIsotonic contraction: contraction against constant load; do workSummation of contractions: muscle DOES NOT have refractory period so repeated stimulation before relaxation added power to contraction already occurringTetanic contraction: repeated stimulation fuse into one continuous contraction; complete if no relaxation between contraction, incomplete if partial relaxtion between; stimulation frequency required determined by twitch duration of fibreTreppe (staircase phenomenon): when max stimuli delivered at frequency just below tetanizing f tension during each twitch increases until same tension per contraction achieved; due to increased availability of Ca for binding trop CTension: total tension – tension developed when muscle stimulated

Passive tension – tension when muscle not stimulatedActive tension – difference between passive and total tension; amount of tension ACTUALLY

generated by contractile processResting length – length of muscle when active tension is maximal

Tension developed proportionate to no. cross linkages between actin and myosinOverstretched – decr overlapToo short – decr distance thin filaments can move on thick

Velocity of contraction is maximal at resting length and declines if longer/shorter

Fibre Types

Type I Type IISlow, oxidative, red Fast, glycolytic, white

ATPase rate Slow FastCa-pumping capacity of SR Mod HighDiameter Mod LargeGlycolytic capacity Mod HighOxidative capacity (no. mitochondria, capillary density, myoglobin content)

High Low

Type I – long, slow, posture-maintaining movementsType II – fine, skilled, short-twitch (eg. Eye, hand)Multiple forms of myosin-heavy chains, tropomyosin and troponin determine diff types of muscle; determined by genes, activity, innervation, hormones

EnergyATP mades by ADP + PO – this needs energy, provided by:

1) Aerobic glycolysis: breakdown of glucose (some from glycogen) pyruvate citric acid cycle respiratory enzyme pathway CO2 + H2O + ATP2) Anaerobic glycolysis: glucose lactate + ATP; does not need O2; produces less E; lactate enters bloodstream but will accumulate in muscles and exceed buffering system decr pH inhibits enzymes so this pathway can only be used for short period of time3) Phosporylcreatine – provided by muscle, hydrolysed at junction between myosin heads and actin creatine and PO releasing energy; at rest ATP used to build up stores4) Lipids free fa’s – not fast enough during exercise; trained athletes can use these better

Oxygen debt: after exertion O2 needed to remove XS lactate, replenish ATP and phosphorylcreatine, replace O2 from myoglobin; trained athletes more efficient so less O2 debtRigor: when muscle completely depleted of ATP and phosphorylcreatine (eg. Death)

Resting heat: heat given off at rest (from BMR)Initial heat: XS heat created during contraction; = activation heat (created whenever muscle contracting) + shortening heat (proportionate to amount muscle shortens)Recovery heat: produced following contraction; metabolic processes restoring muscle to precontractile state; equal to initial heatRelaxation heat: additional released when restore muscle to prev length; requires work

Denervation muscle atrophy abnormal excitability of muscle, incr sensitivity to Ach (denervation sensitivity)

fibrillations (LMN lesion, not visible grossly)

CARDIAC MUSCLE

Functions as synctiumStriatedLarge no. elongated mitochondriaBranching interdigitating muscle fibres – at Z lines they form intercalated discs – strong cell-cell cohesion, pull of one contractile unit transmitted to nextCell membranes of adjacent fibres fuse – gap junctions – bridges for spread of excitationT system located a Z lines (A-I junction in skeletal)

(From pharmacology text book: note)When cell permeable to ion, movement across membrane determined by Ohm’s Law:

Current = voltage Current = voltage x conductance Resistance

Conductance determined by properties of ion channelVoltage determined by diff between actual MP and reversal potential for that ion (ie. MP at which no current would flow if channels were open dependent on elec and chem grads; calculated by Nernst equation) – note K is most important ion hereIn pacemaker cells, spontaneous depolarization occurs during diastole (phase 4) – K concs v important

HyperK decr grad (as intracellular K is usually high), but incr K conductance Decr AP duration, slowed conduction, decr pacemaker rate, decr pacemaker arrhythmogenesissHypoK incr grad but decr conductance prolonged AP, incr pacemaker rate, incr pacemaker arrhythmogenesis

Electrical Properties

RMP = -90mV – affected by extracellular K conc

Phase 0: Depolarisation to threshold rapid (2ms) (affected by extracellular Na conc), with overshoot Opening of activation (m) gates of fast Na channels NA INFLUXMembrane potential approaches +70mV

Na channel has 2 gates: Outer gate – open at start of depolarization (at -70 to -80mV) Inner gate – closes and prevent further influx until AP over

Phase 1: initial rapid repolarisationClosing of inactivation (h) gates of Na channels inactivation

Phase 2: Plateau (200ms)Slower prolonged opening of L-type Ca channels slow CA INFLUX

Phase 3: Repolarisation (not complete until contraction is half over)Closure of Ca channels, opening of K channels K EFFLUX (Ik current)Note, a different K current is found in SAN cells, so durgs can affect Purkinje and ventricular cells but have little effect on SAN repolarisation

Phase 4: Repolarisation complete; h gates of Na channels reopen so they are again ready for excitation

(From pharmacology text book: note)Time between phase 0 and point in phase 3 when Na channels recovered is refractory period; important in suppression / genesis of arrhythmiasNote, RP is important in generation of AP – Na channels close over -75 to -55mV range, so at -60mV less Na channels available than at -80mV; this can alter AP amplitude, excitability, conduction velocity, refractory period; at anything +ive of -55mV there can be no Na currents meaning that AP can only fire due to incr Ca permeability and decr K permeability – this is mechanism in SAN and AVN, and is important in certain arrhythmias

Mechanical Properties

Contraction begins just after start of depolarization; last 1.5x longer than APAbsolute refractory period: until halfway through phase 3 (reaches -50mV); prevents tetanyRelative refractory period: until phase 4

Excitation-contraction coupling similar to skeletalSlow-twitch; low ATPase activity; dependent on oxidative metabolismContains αMHC (higher ATPase activity) and βMHC (lower ATPase activity) (myosin heavy chain) in atria, only βMHC in ventriclesSimilar relation between fibre length and tension as in skeletal; dependent on degree of diastolic filling; pressure in V α total tension developed – Starling’s law of heart – tension will increase as diastolic vol

increases until limit, then will decrease 2Y to disruption of myocardial fibres (NOT decrease in cross-bridges between actin and myosin as in skeletal muscle)Adrenaline activate β1-adrenergic receptors increase cAMP

activates protein kinase A phosphorylation of voltage-dependent Ca channels open longer incr active transport of Ca to SR accelerated relaxation and shorted systole, permitting adequate diastolic filling at incr HR

Digoxin inhibit Na-K-ATPase incr intracellular Na less Na influx less Ca efflux via Na-Ca antiporter incr intracellular CaHypertrophy can occur via mutations of genes coding contractile apparatus; can dilate due to dystrophin gene in muscular dystrophy

MetabolismLarge blood supply; numerous mitochondria, high myoglobin content<1% is anaerobic – may rise to 10% in hypoxia35% E from carbohydrate, 5% ketones, 60% fat (esp. free fa’s)

PacemakerPacemaker tissue has no Na channels so membrane potentials slowly rise when voltage-gated Ca channels open

Arrhythmias (from pharmacology text book)

Caused by:1) Disturbances of impulse formation:

Time between depolarisation of pacemaker cell = duration of AP + duration of diastolic intervalDiastolic interval determined by slope of phase 4 (pacemaker potential) – paraS discharge and beta-blockers slow HR by decr phase 4 slope; hypokalaemia, sym discharge, positive chronotropic drugs, fibre stretch, acidosis and partial depolarisations incr HR by incr phase 4 slope (esp in latent pacemakers such as some Purkinje fibres, although all cardiac cells will display this under correct conditions)Afterdepolarisations: depolarisations that interrupt phase 3 (early, thought to contribute to prolonged QT, worse when slow HR) or phase 4 (delayed, can occur with incr intracellular Ca, thought to cause arrhythmias related to digoxin, NE and MI; worse when fast HR)

2) Disturbances of impulse conduction: can cause block (paraS control of AVN conduction important); re-entry (may be small/large area, may be multiple random or specific anatomical area (eg. WPW); for re-entry there must be:

a) Anatomic/physiological obstacle to conduction for circuit to go aroundb) Unidirectional block at some point in circuitc) Conduction time around circuit must be long enough so retrograde impulse doesn’t enter refractory tissue as it travels around (conduction time > refractory period); slowing of conduction can be due to decr Na/Ca current – drugs that help further decr this current or prolonging refractory period

SMOOTH MUSCLE

Not-striatedActin and myosin not arranged in regular arrays; dense bodies in cytoplasm and attached to cell membrane instead of Z lines, bound to actin by α-actininNo troponinPoorly developed SRFew mitochondria; depend on glycolysis for metabolic needs

Types: visceral/unitary SM – in large sheets; many low resistance gap-junction bridges; syncytial (eg. Hollow viscera walls)

Multiunit SM – individual units without interconnecting bridges (eg. In iris)

Visceral Smooth MuscleElectrical properties: unstable membrane potential – no true resting MP, relatively low when active and high when inhibited – ave -50mV; on top of this are various waves

Slow sine wave-like fluctuationsSpikes – sometimes overshoot 0 potential

May have short duration, may have plateau phase; continuous irregular contractions independent of nerve supply maintained state of partial contractions = tone; excitation-contraction coupling is long process – initiation of contraction after 150ms (10ms in heart/skeletal), peak contraction 500ms after spike

Contraction: since SR poorly developed, Ca must enter from ECF via voltage-gated Ca channels; myosin must be phosphorylated for activation of myosin ATPase

Ach binds muscarinic receptors Ca influx Ca binds calmodulin calmodulin-dependent myosin light chain kinase activated catalyses phosphorylation of myosin light chain incr myosin ATPase activity (differs to skeletal and cardiac muscle where contraction caused by Ca binding troponin C) myosin binds actin contraction myosin dephosphorylated by myosin light chain phosphatase; myosin remains attached to actin for some time after intracellular Ca decreased – latch bridge – sustained contraction – tonic contraction

Note incr cAMP in cardiac muscle incr contraction; in vascular SM decr contraction as it phosphorylates myosin light chain kinase decr affinity for calmodulin

Stimulation: contracts when stretched without any extrinsic innervation; stretch decr MP, incr frequency spikes, incr tone; add epinephrine incr MP, decr f spikes, decr tone; add Ach decr MP, incr f spikes, incr tone

If stretch SM, increased tension will gradually decrease; no resting length can be ascertained – plasticity

Multiunit SMNon-syncytial; contractions don’t spread widely, they are more discrete; contractile response usually irregular tetanus rather than single twitch; long duration of contraction

Synaptic and Junctional Transmission

Impulses transmitted from one nerve cell to another at synapses. Impulse in pre-synaptic cell causes release of neurotransmitter which binds to postsynaptic cell effect which may be excitatory/inhibitory. May be electrical/chemical.Most drugs act on specific receptors that modulate synaptic transmission; RMP of neuron is -70mV

Channels3 types of channels in nerve cells (numerous natural toxins can block these channels):

Voltage-gated: response to changes in MPConcentrated on initial segment and axon, responsible for fast AP transmitting signal from cell body to nerve terminalAlso Ca and K channels on cell body, dendrites and initial segment that are slower and modulate rate at which neuron discharges (eg. K channels open on depolarization of cell, and slow further depolarization)

Ligand-gated (inotropic receptors): open by binding of NT; formed of subunits; activation causes brief opening; responsible for fast synaptic transmissionMetabotropic receptors: G protein linked receptors which NT’s bind; effects can last longer

Modulate voltage-gated channels (usually Ca and K) via G protein eg. Inhibit Ca channel function presynaptic inhibitioneg. Activate K channel slow postsynaptic inhibition

Generally membrane delimited (ie. Local); can also generate diffusible 2nd messengers (eg. cAMP via adenylyl cyclase); can occur over greater distances

SynapsesAP in presynaptic fibre activates voltage-gated Ca channels in synaptic terminal membrane Ca enters synaptic terminal fusion of synaptic vesicles with presynaptic membrane NT released into synaptic cleft NT binds with receptor on postsynaptic membrane change in membrane conductance postsynaptic response (takes 0.5ms, mostly due to time taken for Ca channels to open)

Presynaptic fibre: each nerve divides to form 2000 synaptic endings; form terminal buttons (synaptic knobs) which may end on

Axodendritic – on dendrite/dendritic spineAxosomatic – on cell bodyAxoaxonal – on axon

Contains mitochondria, membrane-enclosed vesicles contains NT’s (made in cell body transported along axon by fast axoplasmic transport; contents of smaller vesicles may be recycled at synaptic ending). Vesicles may be

1) Small, clear synaptic vesicles containing Ach, glycine, GABA, glutamate2) Small vesicles with dense core containing catecholamines3) Large vesicles with dense core containing neuropeptides

The contents are discharged into synaptic cleft:1) Via exocytosis/endocytosis cycle: early endosome buds off vesicles vesicle filled with NT

primed at cell membrane AP exocytosis of contents may undergo endocytosis, hence recycling fuse with endosome; involves use of v-snare protein synaptobrevin in vesicle membrane locking with t-snare protein syntaxin in cell membrane (eg. Large vesicles)

2) Via ‘kiss and run’ discharge: vesicle discharges contents through small hole in cell membrane which reseals rapidly, vesicle always staying inside

Exocytosis occurs from all parts of terminal; small vesicles discharge at areas of membrane thickening called active zones which contain many proteins and rows of Ca channels; Ca influx causes NT release

Neurexins: proteins bound to presynaptic neuron which bind neurexin receptors in postsynaptic neuron; aid to hold synapses together

Synaptic cleft: presynaptic terminal separated from postsynaptic structure by synaptic cleft, 20-40nm wide

Postsynaptic structure: has postsynaptic density – complex of specific receptors, binding proteins and enzymes induced by postsynaptic effects

Tetanus toxin: causes spastic paralysis by blocking presynaptic NT releaseBotulinum toxin: causes flaccid paralysis by blocking release of Ach at NMJ

ReceptorsEvery ligand acts on many subtypes of receptors (eg. Alpha 1,2,3)There are receptors on presynaptic and postsynaptic membrane – presynaptic = autoreceptors, provide feedback controlReceptors usually concentrated in clusters on postsynaptic membrane near neurons that secrete NT’s specific for them, due to presence of specific binding proteins for them (eg. Nicotinic Ach receptor – rapsyn, glutaminergic receptors – PB2-binding proteins, GABA – gephyrin) – receptors bind to the protein in cell membrane during activityProlonged exposure to ligands causes desensitization (eg. In β-adrenergic receptors due to phosphorylation of carboxyl terminal by β-ARK or by binding β-arrestin)

Homologous – loss of responsiveness only to specific ligandHeterologous – loss of responsiveness to all ligands

ReuptakeCan occur via 2 families of transporter proteins:

1) Co-transports NT with Na and Cl (eg. NE. dopamine, serotonin, GABA, glycine, choline)2) Transporters that re-uptake glutamate into neurons/astrocytes coupled to cotransport of Na and

countertransport of KAre also 2 vesicular monoamine transporters (VMAT1, VMAT2) that transport NT’s from cytoplasm to synaptic vesicles (eg. Dopamine, NE, E, serotonin, histamine) – inhibited by reserpineVesicular GABA transporter (VGAT) moves GABA and glycine into vesiclesInhibition of reuptake has big effect – cocaine inhibits reuptake of dopamine, when glutamate reuptake inhibited neuronal damage

Excitatory Postsynaptic PotentialSingle stimulus (excitatory NT on inotropic receptor) transient depolarizing response (but not an actually propagated AP) from depolarization of postsynaptic cell membrane immediately under presynaptic ending (via opening of Na/Ca/K channels in postsynaptic membrane) called excitatory postsynaptic potential (EPSP) – during potential, excitability of neuron to other stimuli increased (if incr presynaptic fibres activated, incr size of depolarization threshold all-or-none AP). Depolarisations produced by multiple synaptic knobs summate:

1) Spatial summation: activity in >1 knob; facilitate eachother to reach firing level2) Temporal summation: repeated stimuli causes new EPSP before old EPSP finished

EPSP is not all-or-none, but proportionate to strength of stimulus

Inhibitory Postsynaptic PotentialStimulation of some input may cause hyperpolarizing rather than depolarizing response via (eg. opening of Cl channels Cl enters postsynaptic cell along conc grad incr membrane potential closure of Na/Ca channels; opening of K channels allowing efflux) decr excitability due to movement of MP away from firing level; peak in 1-1.5ms then decrease over 3ms; decrease excitability; spatial and temporal summation can occur here alsoResults in postsynaptic/direct inhibition

Slow Postsynaptic PotentialsOccur in autonomic ganglia, cardiac muscle, SM, cortical neurons; last several secs; EPSP due to decr K conductance, IPSP due to incr K conductance

Action PotentialsInitial segment has lowest threshold for generation of AP – once fired it goes down axon and retrogradely back into soma; constantly fluctuating MP 2Y to factors above, AP occurs when 10-15mV of depolarization to reach firing level occurs

Synaptic Delay0.5ms delay between impulse reaching presynaptic terminal and response in postsynaptic neuron; due to time it takes for synaptic mediator to be released and cause effect; conduction along chain of neurons slowed by multiple synapses

Inhibition at SynapsesPost-synaptic inhibition: eg. Afferent nerves from muscle spindles EPSP and propagated AP in motor neurons supplying muscle, IPSP in antagonist muscles via inhibitory NT glycinePre-synaptic inhibition: mediated by neurons that end of excitatory endings forming axoaxonal synapses decr NT release; can occur in 3 different ways (eg. GABA) (eg. Used in gating pain transmission):

1) Activation of presynaptic receptor may incr Cl conductance decr size AP reaching excitatory ending decr Ca entry decr amount excitatory NT released

2) Activation open voltage gated K channels K efflux decr Ca influx decr NT released

3) Direct inhibition of NT release Afferent inhibition: inhibition usually caused by stimulation of certain systems acting on one postsynaptic neuron

Negative feedback inhibition: when neuron may inhibit itself (eg. Occurs in spinal motor neurons via inhibitory interneuron, activated by AP in motor neuron, it releases inhibitory mediator to slow/stop discharge at motor neuron). Feed-forward inhibition: when inhibitory cell and excitatory cell both stimulated by same stimulus; limits duration of excitation (eg. Purkinje cells)Neuromodulation: non-synaptic action of substance on neurons which alters their sensitivity to synaptic stimulation/inhibition (eg. Steroids)

Facilitation at SynapsesOpposite to inhibition; eg. Serotonin causes incr intraneuronal cAMP levels phosphorylation of K channels closure of K channels slow repolarisation, prolonged AP

The Brain

Hierarchal systems: All pathways involved in sensory perception and motor control; clearly delineated (made of large myelinated fibres); info processed sequentially at each relay nucleus on way to cortex;Each nucleus contains:

Relay/projection neurons (excitatory; use glutatmate; large axons, many collaterals; transmit signals over long distances) Local circuit neurons (inhibitory; use GABA or glycine; smaller; synapse with projection neurons, inhibiting them; some may from axoaxonic synapses on sensory axons)

3 types of pathways for inhibition: Recurrent feedback pathways Feed-forward pathways

Axoaxonic interactionSince only 3 main NT’s used, drugs can easily target these pathways (eg. GABAa antagonists convulsions)

Nonspecific/diffuse neuronal systems:Involved in more global functions (eg. Sleeping, appetite, emotion)Eg. Monoamines (NE, dopamine, 5-HT), peptide-containing pathwaysEg. Noradrenergic – axons fine and unmyelinated; slow

multiple branching, one neuron can go to many diff parts of CNS fibres studded with varicosities containing vesicles NT’s usually act on metabotropic receptors therefore have longer-lasting effects

Neurotransmitters

May be Amines (eg. Dopamine, norepinephrine, epinephrine, serotonin, histamine)Amino acids (eg. Glutamate, aspartate, glycine, GABA)Polypeptides (eg. Substance P, vasopressin, oxytocin, CRH, TRH, GRH, somatostatin, GnRH, endothelins, enkaphalins etc…)Purines (eg. Adenosine, ATP)Gases (eg. NO, CO)

Excitatory Amino Acids

Gluta -mate

Relay neurons at all levels, some interneurons

NMDA Excitatory: incr cation conductance esp Ca NMDA 2-amino-5-phosphonovalerate, dizocilipine

AMPA Excitatory: incr cation conductance AMPA CNQXKainate Excitatory: incr cation conductance Kainic acid,

domoic acidMetabo – tropic

Inhibitory (presynaptic): decr Ca conductance, decr cAMPExcitatory: decr K conductance, incr IP3 and DAG

ACPD, quisqualate

MCPG

Glutamate: Responsible for 75% excitatory transmission of brainFormation: reductive amination of α-ketoglutarate in cytoplasm glutamate becomes concentrated in synaptic vesicles by transporter BPN1Cytoplasmic store kept high by transporters which import glutamate from interstitial fluid and reuptake it from synaptic clefts via Na-dependent uptake systems, if glutamate is allowed to accumulate excitotoxic damage and cell deathMediates excitatory synaptic transmission by activation of ionotropic and metabotropic receptors:

1) Metabotropic: serpentine G protein linked receptors that act indirectly on ion channels; incr IP3 and DAG levels, or decr intracellular cAMP levels; widely distributed in brain; involved in production of synaptic plasticity; located just outside postsynaptic density

Can be pre-synaptic (group II and III, act as inhibitory autoreceptors via inhibition of Ca channels decr NT release)Can be postsynaptic (group I, activate cation channel, activate PLc incr IP3 intracellular Ca release)

2) Ionotropic: ligand gated ion channels; 3 types Kainite (KA) – simple ion channels; Na influx, K efflux; high levels in hippocampus, cerebellum

and SC may be pre- or post-synapticAMPA – present on all neurons; permeable to Na and K; activation results in channel opening at

RMP; located at periphery of postsynaptic densityNMDA – present on all neurons; highly permeable to Ca, Na and K rise in intracellular Ca

long-lasting enhanced synaptic strength (long term potentiation, LTP) important in learning and memory; only opens in concomitant glycine binding; channel will not open

at RMP due to block of channel by extracellular Mg which is expelled when neuron depolarized (ie. By activation of other channels such as AMPA); located in centre of postsynaptic density

Clearance: glutamate transporters on surrounding glia converted to glutamine by glutamine synthetase released from glia taken up by nerve terminal converted to glutamate by enzyme glutaminase transported into vesicles by vesicular glutamate transporter (VGLUT)Anaesthetics may inhibit NMDA and AMPA receptors

Inhibitory Amino Acids

Typically released from local interneuronsAnaesthetics are thought to work on GABAa and glycine receptors incr Cl conductance

GABA (gamma-aminobutyric acid):

GABA Supraspinal and spinal interneurons GABAa Inhibitory: incr Cl conductance Muscimol Biuculline, picrotoxin

GABAb Inhibitory (presynaptic): decr Ca confuctanceInhibitory (postsynaptic): incr K conductance

Baclofen 2-OH saclofen

Present in whole CNS; transmitter at 20% CNS synapsesResponsible for presynpatic inhibitionFormation: decarboxylation of glutamate catalysed by glutamate decarboxylase metabolized to succinic semialdehyde then succinate by GABA transaminase; cofactor for both these enzymes is pyridoxal phosphateEffect = incr Cl influx, incr K efflux, decr Ca influx hyperpolarisation IPSPReceptors:

GABAa – found in CNS; ionotropic receptors (Cl ion channel) made of 5 subunits; chronically stimulated by GABA in interstitial fluid cuts down on ‘noise’ from incidental discharge of neurons; involved in fast component of IPSP’s; benzo’s bind this

GABAb – found in CNS; metabotropic (coupled to G protein) incr K efflux, inhibit adenylyl cyclase, decr cAMP, inhibit Ca influx (so prevent NT release); involved in slow component (due to indirect coupling of G protein receptor) of IPSP’s; found in perisynaptic region

GABAc – found in retina; Cl ion channel made of 5 subunitsClearance: GABA is reuptook via transporter

2) Glycine

Glycine Spinal and brainstem interneurons Inhibitory: incr Cl conductance Taurine, β-alanine

Strychine

Present in brainstem and SCInhibitory and excitatoryBind receptors that are selectively permeable to ClNB. Activates NMDA receptors

Acetylcholine

Ach Cell bodies at all levels M1 Excitatory: decr K conductance, incr IP3 and DAG Muscarine Pirenzipine, atropine

M2 Inhibitory: incr K conductance, decr cAMP Muscarine, bethanechol

Atropine, methoctramine

Motoneuron-Renshaw cell synapse Nicotinic Excitatory: incr cation conductance Nicotine Dihydro-β-erythroidine, α-bungarotoxin

Important role in cognitive function and memory

Formation: made from choline (made in neurons and reuptook from synaptic cleft) and acetate (activated by combination with reduced coenzyme A) catalysed by choline acetyltransferase acetylcholine taken into synaptic vesicles by vesicular transporter VAChT released into synaptic cleft

Muscarinic receptors – in smooth muscle, brain and glands; M1-M4 are G protein-coupled receptors; affect adenylyl cyclase, K channels or phospholipase C

M1 – in brain; causes slow excitationM2 – in heart; causes slow inhibitionM3+M4 – in smooth muscleM4 – in pancreas increased secretion of pancreatic enzymes and insulin

Nicotinic receptors – in autonomic ganglia, CNS and NMJ; made of 5 subunits that form central channel; when activated α subunit binds Ach change in protein allows passage of Na and other cations depolarizing potential

Clearance: hydrolysed to choline and acetate by acetylcholinesterase in postsynaptic membrane (Pseudocholinesterase: found in plasma, hydrolyses other choline esters; under endocrine control)

Monoamines

Catecholamines: E, NE, dopamineNB. Cocaine blocks reuptake of dopamine and NE Amphetamines cause presynaptic terminals to release NT’s

Formation: all made by hydroxylation and decarboxylation of amino acid tyrosine1) Some tyrosine made from phenylalanine in liver, but most from dietary origin2) Tyrosine transported into catecholamine-secreting (dopaminergic, adrenergic, noradrenergic)

neurons or adrenal medulla3) dopa dopamine in cytoplasm; TYROSINE DOPA is RATE-LIMITING PROCESS4) Dopamine enters granulated vesicles converted to norepinephrine5) transported into vesicles by vesicular transporters6) NE leaves vesicles, is converted to E, then enters other storage vesicles7) Released from neurons by exocytosis

Removed from synaptic cleft by:1) Binding with postsynaptic receptor

2) Binding to presynaptic receptor3) Re-uptake into presynaptic neurons: important for NE4) Catabolism:

a. Oxidation catalysed by monoamine oxidase (MAO-A and MAO-B) on outer surface of mitochondria found esp in neurons; measure 3-methoxy-4-hydroxymandelic acid in urine

b. Methylation catalysed by catechol-O-methyl-transferase (esp in liver, kidneys, smooth muscle, glial cells); accounts for catabolism of extracellular E and NE; measure normetanephrine and meanephrine in urine

Receptors are metabotropic (serpentine with G proteins) - NE has higher affinity for α-receptors E has higher affinity for β-receptors

Norepinephrine – made by noradrenergic neurons; at most sym postganglionic endings; noradrenergic neurons located in reticular formation, but most regions of CNS receive input; all receptors are metabotropic; stored in synaptic knobs in small granulated vesicles; NE and E bound to ATP and associated with protein called chromogranin A in vesicles; may also contain neuropeptide Y and dopamine beta-hydroxylase which get released with NE + E on exocytosis; can hyperpolarize neurons by increasing K conductance, or may enhance excitatory output via disinhibition or blockage of K channels

NE Cell bodies in pons and brainstem, project to all levels

α 1 Excitatory: decr K conductance, incr IP3 and DAG Phenylephrine Prazosinα 2 Inhibitory (presynaptic): decr Ca conductance, incr

K conductance, decr cAMPClonidine Yohimbine

β 1 Excitatory: decr K conductance, incr cAMP Isoproterenol, dobutamine

Atenolol, practolol

β 2 Inhibitory: incr Na conductance, incr cAMP Albuterol Butoxamine

Dopamine – slow inhibitory effect on CNS neurons; mainly used in projection linking substantia nigra to neostriatum (function of antiparkinsonian drugs), and projection to limbal structures (function of antipsychotic drugs), and in hypothalamus; in small intensely fluorescent (SIF) cells; receptors are all metabotropic; reuptake via Na and Cl-dependent transporter; metabolized via MAO and COMT

D1-like receptors: D1, D5D2-like receptors: D2, 3, 4

Dopa -mine

Cell bodies at all levels D1 Inhibitory: incr cAMP PhenothiazinesD2 Inhibitory (presynaptic): decr Ca

Inhibitory (postsynaptic): incr K conductance, decr cAMP

Bromocriptine Phenothiazines, butyrophenones

Tyrosine hydroxylase gets negative feedback from dopamine and norepinephrine; tyrosine hydroxylase needs a co-factor named tetrahydrobiopterinPhenylketonuria: build up of phenylalanine 2Y to mutation of gene for phenylalanine hydroxylase; NE and E can still be made from tyrosine; if caused by deficiency of tetrahydrobiopterin, since this is involved in many steps above as cofactor, will also get deficiency of NE and E

Serotonin (5-hydroxytryptamine)

5-HT Cell bodies in midbrain and pons; project to all levels

5-HT1A Inhibitory: incr K conductance, decr cAMP LSD Metergoline, spiperone

5-HT2A Excitatory: decr K conductance, inc IP3 and DAG LSD Ketanserin5-HT3 Excitatory: incr cation conductance 2-methyl-5-HT Ondansetron5-HT4 Excitatory: decr K conductance

Found in enterochromaffin cells, myenteric plexus, brain (pons and upper brainstem), retina; found in unmyelinated neurons that innervate most regions of CNSInhibitory – usually via 5-HT1a (membrane hyperpolarisation via incr K conductance); 5-HT3 or 4 may be slow excitatory; may be excitatory and inhibitory on same neuron; involved in sleep, temp, appetitie, neuroendocrine controlFormation: hydroxylation and decarboxylation of aa tryptophanDeactivated by: reuptake

Breakdown to 5-hydroxyindoleacetic acid by MAO Converted to melatonin by pineal gland

Multiple receptors, all metabotropic (coupled to adenylyl cyclase or phospholipase C) except 5-HT3 which is ionotropic

5-HT2A – for platelet aggregation and SM contraction5-HT2C – mediate food intake5-HT3 – in GI tract, related to vomiting5-HT4 – in GI tract, related to peristalsis and secretion

HistamineHistaminergic neurons have cells bodies in tuberomammillary nucleus of post hypothalamus axons to all brain; also found in gastric mucosa and mast cells (in pituitary gland)

Formed by decarboxylation of aa histidine; most histamine is converted to methylhistamineH1-3 are known – found in peripheral tissues and brain; related to arousal and sexual behaviour, BP, pain threshold, itch

H1 – activate phospholipaseH2 – increase cAMPH3 – mostly presynaptic, work in negative feedback

Tachykinins

Substance P: receptor is serpentine acting via G protein activation of phospholipase C, formation of IP3 and DAG slow EPSP in neurons transmitting noxious stimuli; involved in slow pain; also found in nigrostriatal system and hypothalamus, involved in peristalsis in intestineOther tachykinins are neurokinin A, neuropeptide K, neurokinin B

Opioid Peptides

Opioid peptides

Cell bodies at all levels Mu Inhibitory (presynaptic): decr Ca conductance, decr cAMP

Bendorphin Naloxone

Delta Inhibitory (postsynaptic): incr K conductance, decr cAMP

Enkephalin Naloxone

Kappa Inhibitory (postsynaptic): incr K conductance, decr cAMP

Dynorphin Naloxone

Enkephalins bind opioid receptors (eg. Met-enkephalin and leu-enkephalin); found in GI tract and brain; decr intestinal motility, pain relieving; they come from precursors from which the peptide is cleaved

Prokephalin met-enkephalin, leu-enkephalin, octapeptide, heptapeptidePro-opiomelamocortin beta-endorphin, other endorphinsProdynorphin dynorphins, neoendorphins

Enkephalins are metabolized by enkephalinase A and B and aminopeptidase3 receptors characterized, serpentine receptors coupled to Gq, inhibit adenylyl cyclase:

μ – analgesia, resp depression, constipation, euphoria, sedation, miosis, incr secretion GH and PL; incr K conductance hyperpolarisation; bind endorphins

κ – analgesia, diuresis, sedation, miosis, dysphoria; close Ca channelsδ – analgesia; close Ca channels; bind enkephalins

Other PolypeptidesSomatostatin: sensory input, locomotor activity, cognitive function; inhibits insulin secretion from pancreas, inhibits GI hormones; 5 different G protein coupled receptorsVasopressin, oxytocin, neurotensin, cholecystokinin, VIP, neuropeptide Y

Purine and Pyrimidine TransmittersATP: released with other NT’s during exocytosis; may act via G proteins or ligand-gated ion channelsAdenosine: general CNS depressant; vasodilator in heart; works via different serpentine G protein linked receptors changing cAMP concs

GasesNO: made from arginine catalysed by NO synthase; activates guanylyl cyclase

Endocannabinoids

Triangle9-THC is psychoactive ingredient of cannabis; activates receptor CB1 (also activated by endogenous anandamide and 2-arachidonylglycerol) – can function as retrograde synaptic messengers (released from POSTsynaptic neurons activate CB1 on PREsynaptic neurons suppress NT release)

CotransmittersWhen NT released with eg. A polypeptide – one may potentiate the effect of another

Synaptic Plasticity and LearningPosttetanic potentiation: enhanced postsynaptic potentials in response to stimulation; enhancement lasts up to 60secs; tetanising stimulation causes accumulation of Ca in presynaptic neuron until intracellular binding sites are saturatedHabituation: when benign stimulus is repeated, response to stimulus decreases; due to decr release of NT from presynaptic terminal 2Y to decr intracellular Ca due to gradual inactivation of Ca channels

Sensitisation: prolonged occurrence of augmented responses after a stimulus to which animal has been habituated is paired with noxious stimulus; may be transient/longer term; due to Ca-mediated change in adenylyl cyclase incr production cAMPLong term potentiation: persistent enhancement of postsynaptic potential response to presynaptic stimulation after brief period of rapidly repeated stimulation; much more prolonged than posttetanic potentiation; due to accumulation of Ca in postsynaptic neuronLong term depression: decreased synaptic strength

NEUROMUSCULAR TRANMISSION

NMJAs axon approaches termination, loses myelin sheath and divides into terminal buttons/endfeet contains small clear vesicles containing Ach; endfeet fit into junctional folds (depressions in motor end plate – thickened part of muscle membrane, containing 15-40 million Ach receptors); 1 nerve fibre per end plate, no convergence of multiple inputs

1) Impulse arrives at end of motor neuron2) Incr permeability to Ca Ca INFLUX3) Incr exocytosis of Ach-containing vesicles (approx 60 per impulse, each vesicle containing 10,000

Ach molecules – 10x more than needed to depolarize)4) Ach diffuses to nictonic receptors5) Incr Na and K conductance of muscle membrane Na INFLUX depolarizing end plate

potential6) Adjacent muscle membrane depolarized to firing level AP conducted down fibre muscle

contraction7) Acetycholinesterase removes Ach from synaptic cleft

Drug curare competes with Ach at endplate; endplate potentials undergo temporal summationAt rest, small quanta of Ach (size proportional to Ca, inversely propotional to Mg at end plate) released randomly miniature end plate potential (0.5mV)Myasthenia gravis: ab to nicotinic receptors destroy receptors or trigger removal by endocytosisLambert-Eaton syndrome: antibodies to Ca channels in nerve endings decr Ca influx prevents Ach releaseDenervation hypersensitivity: when motor nerve to muscle cut, muscle becomes v sensitive to Ach, but muscle atrophies; this only affects the structure immediately innervated by neurons, not those further downstream; due to synthesis of more receptors; will result in wallerian degeneration with also retrograde degeneration up to site of nearest sustaining collateral; in cell body chromatolysis occurs (decr in Nissl substance); then regenerative sprouting with axon beginning to regrow – this can be helped by giving neurotrophins

Smooth and Cardiac MusclePostganglionic neurons branch extensively and have beads (varicosities) not covered by Schwann cells containing vesicles; may contain clear vesicles with Ach, or dense-core vesicles with NE; NO END PLATES – nerve fibres run membranes of muscles cells, so 1 neuron can innervate many effector cells (synapse en passant); fibres end on SAN, AVN, and Bundle of His (NE fibres also innervate ventricular muscle)In smooth muscle NE partial depolarization called excitatory junction potentials (EJP’s); or partial hyperpolarisation called inhibitory junction potentials (IJP’s) depending on whether NE is excitatory or not to that tissueDenervation hypersensitivity: when motor nerve to muscle cut, muscle becomes v sensitive to Ach; muscle DOES NOT atrophy

IMPULSES IN SENSE ORGANS

Sensory receptors transduce energy from environment (eg. Thermal, light, odour, taste) into AP’s in neurons; may be part of neuron or specialized cell that generates AP in neurons; receptor has much lower threshold to respond to adequate stimulus than other receptors (eg. For rods, this is light – will respond to pressure on eyeball however, but has to be higher stimulus); there are 11 conscious senses

Classification: special (smell, vision, hearing, rotational and linear acceleration, taste), cutaneous (touch-pressure, cold, warmth, pain – receptors for this likely on naked nerve endings, CMR-1 for mod cold, VR1 and VRL-1 for extreme heat, latter 2 are nociceptive), visceral. Or teleceptors (events at a distance), exteroceptors (external enviro near), interoceptors (internal enviro), proprioceptors (position)

Pacinian corpuscule: touch receptor; unmyelinated ending of sensory nerve fibre; large; surrounded by connective tissue; myelin sheath begins in corpuscule; responds only to transient touch; when small amount of pressure applied nonpropagated depolarizing potential occurs – generator/receptor potential generator potential proportionate to magnitude of stimuli at 10mV AP generated, fires repetitively if pressure further increased sensory nerve at 1st node of Ranvier depolarized propagated. Frequency of AP’s proportionate to magnitude of applied stimuli.

Adaptation/desensitisation: when maintained stimulus, frequency of AP’s decreases over time; this may beRapidly adapting: eg. Light touchSlowly adapting: eg. Muscle spindles, nociceptive

Doctrine of specific nerve energies: sensation evoked by receptor is due to specific part of brain they ultimately activate (eg. Irritation from a tumour in armpit on sensory nerve from pacinian corpuscule in hand will cause sensation of touch)

Projection: no matter where in pathway is stimulated, sensation is referred to location of receptor (eg. Phantom limb)

Intensity discrimination: vary frequency of AP, or vary no. receptors stimulatedR (sensation felt) = K(constant) x S(intensity of stimulus)A(constant)

Sensory unit: single sensory axon and its many peripheral branches supply a receptive field; as strength of stimulus increases it activates sense organs immediately in contact with it and recruits those in surrounding area as receptive fields overlap; stronger stimuli will also stimulate receptors with higher thresholds increase intensity of sensation

REFLEXES

Reflex arc: sense organ Needs adequate stimulusReceptor potential proportional to strength of stimulus all-or-none potential in…

AFFERENT neuron Enter via dorsal roots/CN; cell bodies in dorsal root ganglia/CN gangliaNo. potentials proportionate to size of generator potential

Synapses in central integrating system (eg. Brain/spinal cord) EFFERENT neuron (the final common path)

Leave via ventral roots/motor CNReceive multiple other inputs

Effector

In above, spatial and temporal facilitation, occlusion, subliminal fringe effects all occurCNS can be in central excitatory/inhibitory state (eg. When excitatory, impulses radiate not only to somatic areas but also to autonomic areas (eg. Urination, sweating, - mass reflex)). Habituation and sensitization can be applied to reflexesBell-Magendie law: dorsal roots sensory, ventral roots motor

Monosynaptic reflex: eg. Stretch reflex (muscle spindle fast sensory fibres NT at central synapse = glutamate motor neuron muscle)

Muscle spindle:

10 intrafusal muscle fibres enclosed in CT capsule, ends of which are contractile and attached to tendons at either end of muscle or to sides of extrafusal fibres.

2 types of intrafusal muscle fibre:1) Nuclear bag fibre: many nuclei in central dilated area; 2 fibres per spindle, 1 with high and 1

with low ATP-ase activity2) Nuclear chain fibre: thinner, shorter, no central bag; 4+ per spindle; attached to 1)

Respond to changes in length and changes in rate of stretch:Stimulation of NBF’s dynamic fusiform response (ie. Discharge most rapidly when muscle being stretched, less rapidly during sustained stretch) – physiologic tremor would be worse if it wasn’t for NBF’s being sensitive to rate of stretchStimulation of NCF’s static fusiform response (ie. Discharges rapidly so long as muscle is stretched

Motor nerve supply1) Exclusive motor nerve supply (γ efferents of Leksell / small motor nerve system) – 3-6um diameter, 30% fibres in ventral roots, group A γ; have motor end plates (plate endings) on NBF’s and trailing endings on NCF’s

Stimulation causes contractile ends of intrafusal fibres to shorten (become shorter than extrafusal fibres) stretches NBF’s stimulates Ia sensory fibres may cause reflex contraction of muscle (via α motor neurons); as there is α-γ linkage, spindle shortens with muscle during contraction, so spindle discharge may continue throughout contraction, so spindle remains capable of responding to stretch; regulated by descending tracts from brain, regulating sensitivity for posture etc… (discharge incr by anxiety, unexpected mvmt, Jendrassik’s manouvre, noxious stimulus to skin)

INCR DISCHARGE INCREASES SPINDLE SENSITIVITY3) β motor neurons – have motor end plates (plate endings)

There are also γ and β dynamic and static efferents – stimulation of dynamic efferents increases spindle sensitivity to rate of stretch; stimulation of static efferents increases sensitivity to steady, maintained stretch

Sensory nerve supply1) Primary (annulospiral) ending: the terminations of rapid Ia sensory afferent fibres; 1 branch innervates NBF 1 and another NBF 2 and NCF’s; nerve endings wrap around centre of fibres and go to motor neurons supplying extrafusal fibres of same muscle2) Secondary (flowerspray) ending: the terminations of II sensory fibres; near ends of intrafusal fibres on NCF only

Stimulation caused by stretching of muscle spindle receptor potential AP in Ia fibres at f proportionate to degree of stretching spinal cord motor neuron to extrafusal fibres (monosynaptic)

Reaction time: time between application of stimulus and response (eg. 19-24ms for knee jerk)Central delay = reaction time – time taken for impulse to travel to and from spinal cord = time

taken for reflex activity to traverse spinal cord (0.6-0.9ms)II sensory fires may be involved in polysynaptic mechanisms.Feedback device that maintains muscle length – if stretched, reflex contraction; if shortened, reflex relaxation

Reciprocal innervation: Ia fibres cause postsynaptic inhibition of motor neurons to antagonists via inhibitory interneron (Golgi bottle neuron) – BISYNAPTIC

Inverse stretch reflex/autogenic inhibition: when tension becomes so great that there is no longer reflex contraction muscle relaxes; note, elastic muscle fibres take up much of stretch so takes strong stretch to cause relaxation; receptor is in Golgi tendon organ (net-like knobbly nerve endings along fasiscles of tendon; 3-25 muscle fibres per organ, Ib myelinated rapidly-conducting sensory nerve fibres; stimulated by both passive stretch and active contraction of muscle – acts as feedback circuit to regulate muscle force; low threshold)

Stimulation spinal cord inhibitory interneuron generation of IPSP’s on motor neuron that supply that muscle, excitatory connections to motor neurons supplying antagonist muscle

Tone: flaccid is α neurons cuts hypotonic if γ efferent discharge low hypertonic if high (if you lengthen muscle passively, it wants to contract, so high tone further

stretch causes inverse stretch reflex, sudden loss of resistence – clasp-knife effect/lengthening reaction); clonus – regular rhythmic contractions in muscle exposed to sudden sustained stretch (spindle hyperactive so bursts of impulses discharge motor neurons all simultaneously muscle contraction stops spindle discharge we keep pushing and cause passive stretch again…)

ALL THE ABOVE DETERMINE RATE OF DISCHARGE OF α MOTOR NEURONS- SPINDLES FEEDBACK TO REGULATE MUSCLE LENGTH- GOLGIS FEEDBACK TO REGULATE MUSCLE FORCE

Polysynaptic Reflexes

Synaptic delay = approx 0.5ms, so the more synapses the slower the response’

Reverberating response: some pathways may turn back on self, activity reverberates until unable to cause propagated reponse dies out

Withdrawal reflex: nociceptive stimulus flexion of agonist, inhibition of antagonist; it is prepotent (ie. Take priority over any other reflex activity occurring in spinal cord at that moment)Crossed extensor response: with withdrawal reflex, also get extension of contralateral limbIrradiation of the stimulus: when spinal cat’s paw pinched, limb withdrawn, contralateral hindlimb extended, ipsilateral forelimb extended, contralateral forelimb flexed – spread of excitatory impulses up and down spinal cord causing recruitment of motor unitsLocal sign: if noxious stimulus is medial aspect leg, also get some abduction of legFractionation: each input only goes to part of motor neuron pool for the flexors so doesn’t produce maximal responseOcclusion: various afferent inputs share some motor neurons submaximal responseStronger stimulus causes larger and more prolonged response due to repeated firing of motor neurons (after-discharge – due to continuing stimulation of motor neurons along a polysynaptic path, many impulses arriving at different times). Stronger stimulus causes faster response due to temporal and spatial summation in polysynaptic pathway.

SENSATION

Cell bodies in dorsal root gangliaDorsal horns arranged into laminas I-VII (I most superficial)

I-VI: unilateral inputII, III: substantia gelatinosaVII: bilateral input

3 types of sensory fibres:1) Aα and Aβ fibres: large, myelinated; mechanical stimuli; III-VI2) Aδ fibres: small, myelinated; mechanoreceptors (III + IV), cold, fast nociceptors (I + V)3) C fibres: small, unmyelinated; pain, temperature, mechanoreceptors (I + II)

Pathways

Dorsal column / lemniscal system (fine touch (localization, spatial form, temporal pattern) and proprioception)

Travel up dorsal column synapse in MEDULLA (gracile and cuneate nuclei)

cross midline IN MEDIAL LEMNISCUS ventral posterior nucleus in thalamus

Damage loss of vibratory sensation and proprioception, loss of localization of touch sensation, incr touch threshold, decr no touch-sensitive areas in skinSome collaterals synapse in dorsal horn, may modify input into other cutaneous sensory systemsDorsal horn acts as a ‘gate’ allowing certain pain impulses through depending on impulses from descending tracts from brain and nature of input Lower axons more medial

Anterolateral system / spinothalamic (touch (gross), pain, cold, warmth): Synapse in dorsal horn cross midline IN SPINAL CORD locally ascend in anterior spinal cord (touch)

lateral spinal cord (pain and temp) relay nuclei in thalamus, projection nuclei near midline, reticular activating system

Damage incr touch threshold, decr no touch-sensitive areas; touch localization normal; deficit less profound than dorsal columnsLower axons more lateral

From thalamus sensory info goes to cortex:Somatic sensory area I (Brodmann’s area 1, 2 and 3): in postcentral gyrus; legs at top and head at

Bottom; hand and mouth have large amounts; cells organized in vertical columns, each column responds to a certain sensory modality

Ablation deficits in position sense, discrimination of size and shape; also effects SII (hence SI processes stuff then projects it on to SII)

Somatic sensory area II: in superior wall of sylvian fissure (separated temporal from frontal and parietal lobes); head at inf end of postcentral gyrus, feet at bottom of sylvian fissure

Ablation deficits in tactile discrimination; has no effect on SI

Cortical plasticity: above mapping can change rapidly to reflect use of represented area; cortical connections of sensory units to cortex have convergence and divergence, connections can become weak/strong with disuse/use; this doesn’t only occur with touch

Cortical lesions mainly effect proprioception and fine touch, affect temp and pain to lesser extent.

TouchNot necessarily visible specialized receptors; numerous in fingers and lips, around hair folliclesReceptor: associated with BNC1 Na channel (a degenerin – when hyperexpressed, cause neurons they are in to degenerate)Nerve: Aβ (5-12um diameter, conduction velocity 30-70m/s) and C fibresPathway: transmitted in dorsal (more important) and spinothalamic columns, so rare to get complete loss

ProprioceptionNerve: AαPathway: dorsalCentral: cerebellum, medial lemniscus, thalamusNB. ‘Spray’ endings, touch receptors in skin, muscle spindles all convey info along antlat column to cortex for conscious awareness of position of body

TemperatureMore cold sensitive (10-38deg) than heat sensitive (30-45deg) spotsReceptor: from the TRP family of cation channels

Moderate cold – cold- and menthol-sensitive receptor 1 (CMR1) Severe heat – VR1 and VRL-1 (both nociceptors)

Nerve: Aδ + C for cold, C for hotPathway: spinothalamic column

Central: postcentral gyrus, insular cortex

PainSense organ: naked nerve endings; vanilloid receptor-1 (VR1) and VRL-1 discovered which respond to pain, protons, harmful tempsNociceptive substances: P factor (?may be K) causes pain in muscles not receiving enough blood supply, washed away when blood returnedNerve: Aδ (small myelinated, 2-5um diameter, 12-30m/s) terminate in dorsal horn on lamina I + V; fast

Pain (sharp); deficiency in deep structures Dorsal root C fibres (large unmyelinated, 0.4-1.2um diameter, 0.5-2m/s) terminate in dorsal horn

lamina I + II; slow pain (dull)Neurotransmitter: mild pain = glutamate, severe pain = substance P - from 1Y afferent to dorsal cordPathway: some in dorsal, some in lat spinothalamicCentral: to ventral post nuclei in thalamus cortex (areas SI, SII, cingulates gyrus, mediofrontal cortex, insular cortex, cerebellum) Visceral pain: no proprioceptors, few temp or touch, sparse pain receptors (sensitive to distension and chemical irritation); afferent fibres reach CNS via paraS and sym fibres (splanchnic, pelvic, phrenic, intercostal, facial, GP, vagus, trigeminal) cell bodies in dorsal roots and CN ganglia travel in spinothalamic tracts, or may make connections with collaterals to postganglionic sym neurons for reflex control reflex contraction of nearby skeletal muscleReferred pain: visceral / deep somatic to somatic structure; may appear to radiate; referred to structure developed from same embryological segment / dermatome (dermatomal rule); due to plasticity of CNS and convergence of pain fibres on same 2nd order neurons (lamina 1-VI ipsilateral, lamina VII bilateral, hence can be referred to opp side of body) – peri neurons don’t usually fire the 2nd order neuron, but if visceral stimulation prolonged facilitation occurs at peri endingsCentral inhibition: inhibition of pain pathways in dorsal horn gate due to stimulation of large-diameter touch-p afferentsInflammatory pain: exaggerated response (hyperalgesia) and pain on normally non-painful stimuli (allodynia); due to release of cytokines and GF’s facilitating perception and transmission in cut areas and dorsal hornNeuropathic pain: causalgia – burning pain after trivial injury; reflex sympathetic dystrophy – skin thin, shiny, incr hair growth; nerve inj causes growth of sym nerve fibres into dorsal root ganglia of sensory nerves from injured area sym discharge causes painAnalgesics: opiates can work peripherally in tissue, in dorsal horn where 1Y afferent synapses, in brainstem (activate inhibitory descending pathways that decr transmission of pain impulses); placebo can cause release of endogenous opioids

Itch and TicklePathway: spinothalamicRelieved by scratching as activates large, fast-conducting neurons that gate transmission at dorsal horn

Synthetic SensesTouch, warmth, cold, pain cortex makes vibratory sensation, 2-point discrimination, stereognosisVibration: pacinian corpuscules dorsal column2-point discrimination: smallest where touch receptors most numerous; back = 65mm, fingers = 3mmStereognosis: ability to identify objects by handling them; also dorsal column

VISION

AnatomySclera: protective outer coveringCornea: transparent Choroid: BV’s

Retina: lining post 2/3 of choroid, neural tissue, extends almost to ciliary body (containing circular and longitudinal muscle fibres; makes aqueous humour that nourishes cornea and lens enters ant chamber through canal of Schlemm at iridocorneal angle

Accomodation: must contract relax lens ligaments if object >6m away Near point of vision is closest object can be focused – 9cm aged 10, 83cm aged 60 (presbyopia) due to hardness of lensNear response: accommodation + convergence of visual axes + papillary constriction

Lens: held in place by lens ligament (zonule) attached to thickened choroid (ciliary body)Parallel (ie. >6m away) light rays strike biconvex lens are refracted (at cornea, ant lens and post lens) to point (principle focus) which is on line passing through centres of curvature of lens (principal axis); distance between lens and PF is principal focal distance (will be longer if object <6m away); refractive power increases with curvature of lens (measured in diopters)Hyperopia: short eyeball, far sighted; make up for this with sustained accommodation, but prolonged convergence of visual axes may cause strabismus; need convex lensesMyopia: long eyeball, short sighted; correct with biconcave lensesAstigmatism: irregular corneal curvature; part of retinal image is blurred; need cylindric lenses

Iris: contains circular and radial muscles that change pupilPupillary light reflex assoc with consensual light reflex (pathway is dorsal to that for near response so can lose response to light but retain accommodation – Argyll Robertson pupil)

Nerves leave near lat geniculate bodies to enter midbrain at sup colliculus terminate in pretectal nucleus 2nd order neurons to ipsilateral and contralateral Edinger-Westphal nucleus 3rd order neuron to ciliary ganglion in oculomotor nerve 4th order neuron to ciliary body)

Vitreous humour: between lens and retinaMacula lutea: near post pole of eye, location of fovea centralis (rod free, dense cones which each synapse with only 1 bipolar cell which synapses with 1 ganglion cell; high VA)Lacrimal gland: moistens cornea lacrimal duct

Photoreceptor Mechanism

Visible light 397-723nm wavelengthDARK: Na channels in outer segments open current flows from outer to inner segment and to synaptic ending; Na-K-ATPase in inner segment maintains ionic equilibrium; steady release of NTLIGHT: closure of some Na channels hyperpolarizing receptor potential decr release of NT signal in bipolar cells AP in ganglion cells optic nerve

Light absorbed by photosensitive pigments change in structure electrical responsePigments made of opsin (protein) and retinene (aldehyde of vit A1; vit A def causes visual abnormalities eg. Nyctalopia – night blindness, prolonged def causes degeneration of neural tissues)

RODS: Rhodopsin (visual purple): made of scotopsin and retinene1 (can be made from vit A); peak sensitivity wavelength 505nm; molecular weight 41000; makes up 90% of protein in rod’s membranes; serpentine receptor coupled to G protein (transducin, Gt1); light changes shape of retinene1 (from cis-11 config to all-trans isomer)

alters configuration of scotopsin activates G protein exchanges GDP for GTP α subunit separates (active until GTPase hydrolyses GTP, which is accelerated by β-arrestin) activates cGMP phosphodiesterase converts cGMP (which normally keeps Na channels open) to 5’-GMP Na channels close hyperpolarizing potential; reaction amplifies light signal retinene1 separates from scotopsin (bleaching) some converted back to 11-cis config by retinal isomerase reassociates with scotopsin rhodopsin

CONES: 3 diff types responding to wavelengths 440 (blue, short/S, blue-violet portion)535 (green, Middle/M, green portion)565 (red, long/L, yellow portion) nm

Each contains different pigment which is maximally sensitive to one of 1Y colours (Young-

Helmholtz theory); green and red pigment similar, blue different; contains an opsin and retinene1; light activates retinene1 activates Gt2 activates phosphodiesterase cGMP to 5’-GMP closure of Na channels between ECF and cone cytoplasm decr intracellular Na hyperpolarisation

Light also decr Ca conc changes which speed recovery, reopening Na channels activates guanylyl cyclase makes more cGMP inhibits light-activated phosphodiesterase

Axons that go to suprachiasmatic nuclei and lat geniculate nuclei contains melanopsin instead of above

Cone receptor potential – sharp onset and offset; cone responses α stimulus intentity at high levels of light when rod response are at max and don’t changeRod receptor potential – sharp onset, slow offset; rod responses α stimulus intensity at levels of light lower than threshold for cones; better at detecting absolute illumination

Genetics

Gene for rhodopsin on C3; for blue-sensitive cone pigment on C7, for red and green sensitive cone pigment on q arm of CX – recombination results in shifted spectral sensitivitiesDichromats only have 2 colour pigments; trichromats have all 3; monochromats have only one-anomaly = colour weakness; -anopia = colour blindness; prot- = red; deuter- = green; trit- = blueColour blindness usually inherited (8% males, 0.4% females; recessive X-linked), but can be caused by lesions of V8

Retina10 layers; contains rods and cones

synapse with bipolar cells (rod bipolar cells for rods, flat bipolar cells for cones) (signal may be altered by horizontal cells) synapse with ganglion cells (105:1 convergence)

Signal may be altered by amacrine cellsLarge/M/magno ganglion cells for movement, depth, flicker and stereopsisSmall/P/parvo ganglion cells for colour, texture, fine detail and shape Ganglion cells subtract/add input from one type of cone to input from another

axons converge and form optic nerve 3mm medial to post pole of globe @ optic disc which is blind spot as no rods/cones there decussate at optic chiasm optic tract

to hypothalamus endocrine and circadian rhythms for light-dark cycleor lat geniculate body (in thalamus)

Contains 6 layers; 1+2 have large cells, magnocellular, receives M ganglion cells 3-6 have small cells, parvocellular, receive P ganglion cellsInterlaminar region receives P ganglion cells1+4+6 input from contralat eye2+3+5 input from ipsilat eye

Precise representation of retina; input not only from retina, but also cortex for perception of orientation and motionUpper retina (lower visual field) to medial half; lower retina (upper visual field) to lat half

to geniculocalcarine tract (divergence, 2x more fibres than in optic nerve) – med geniculate body to superior calcarine fissure, lat to inf, from macula to post meaning macular sparing is possible) via magnocellular and parvocellular pathways

3 different pathways – red/green pathway (difference between L+M) blue/yellow pathway (difference between S+L/M) luminance pathway (sum of L+M)

occipital lobe (Brodmann’s area / 1Y visual cortex / V1 at calcarine fissure); 1000x more nerves involved than in optic; precise mapping of retina; arranged in vertical columns depending on orientation in degrees; also has 6 layers

Parvo and magnocellular to layer 4Interlaminar region to layer 2+3 (have clusters of cells containing cytochrome oxidase called blobs, for colour vision)Feature detectors: half receive input from both eyes

Simple cells respond to bars of light, lines, edges at certain orientationsComplex cells less dependent on location of stimulus in visual field

project from V1 to dorsal/parietal pathway – for motion ventral/temporal pathway – for recognition of forms and faces connect with sensory areas area V8 – for colour vision

or pretectal region of midbrain and sup colliculus papillary reflexes and eye mvmtThese fibres leave optic tract near geniculate bodies so blindness with papillary reactions due to lesion behind optic tract

or frontal cortex control of saccades, vergence and near response

Rods and cones rest on pigment epithelium next to choroid (ie. Deep) so light must pass through ganglion an bipolar cell layer to reach them; pigment epithelium absorbs light, preventing it’s reflection, preventing blurring of vision; have outer segment (modified cilia, discs composed of membrane which contain photosensitive compounds that initiate AP’s), inner segment (has nuclear region, rich in mitochondria) and synaptic zoneRod: 12 million; has saccules rather than discs; thin outer segments constantly renewed by formation of new discs at inner edge with phagocytosis of old discs at outer edge; predominate extrafovealy, much convergence; sensitive receptors for night vision (scotopic)Cones: 6 million; has discs; thick inner segments, conical outer segments; diffuse renewal at multiple sites; higher threshold for bright vision (photopic)Duplicity theory: input from rods and cones

Horizontal cells: connect receptor cells to one another in outer layerAmacrine cells: connect ganglion cells to one another in inner layerGap junctions; connect retinal neurons to one anotherMuller cells: bind neural elements togetherRetinal BV supply bipolar and ganglion cells, choroidal BV for rods and cones

Only ganglion cells have all-or-none AP’s; others have local, graded potentialsRods, cones and horizontal cells – hyperpolarizingBipolar cells – hyper/depolarizingAmacrine cells – depolarizing which may act as GP for ganglion cells

Image Formation

When there is light, the surrounding area is inhibited mediated by hyperpolarisation of horizontal cells inhibits response of photoreceptor (lateral / afferent inhibition); helps sharpen image and improve discriminationProcessing occurs by amacrine cells Dopamine affects structure of gap junctions, allowing current to pass freely between horizontal cells in dark, enlarging receptive field

Dark adaptation: max at 20mins; due to adaptation of rods; time due to time required to build up rhodopsin stores as in bright light much has been broken downLight adaptation: 5 mins

Colour Vision

Hue, intensity, saturationComplementary colour: ever colour has a colour that combines with it to produce whiteBlack: absence of colourColour perceived depends on colour of other objects in visual fieldPrimary colours - Red light: 723-647nm

Green light: 575-492nmBlue light: 492-450nm

Visual AcuityDegree to which details and contours of objects perceivedMin seperable: shortest distance 2 lines can be apart

Critical Fusion Frequency: f at which stimuli can be presented and still be perceived as separateBinocular vision: images from 2 retinas fused at cortical level; points on retina on which image must fall to be seen as single images are corresponding pointsStrabismus: when images no longer fall on corresponding points; in young children diplopia settles when one image is suppressed (suppression scotoma) – occurs in cortex, permanentAmbylopia ex anopsia: suppressed vision when refractive error in one eye

Eye MovementsWhen eye looking nasally – IO elevates, SO depressesWhen eye looking laterally – SR elevates, IR depressesSaccades: sudden jerking movement; bring objects onto fovea; prevent adaptation that would occur if gaze fixed on one object for long time; in frontal cortex and sup colliculi (innervated by M fibres, and from cerebral cortex; projections to cerebellum and areas for reflex mvmt of head and nect via tectospinal tract)Smooth pursuit movement: tracking; cerebellumVestibular movement: due to stimuli from semicircular canals, maintain as fixation as head movesConvergence movement: focus near

HEARING AND EQUILIBRIUM

Anatomy:

Eustachian tube: opens into nasopharynx; opens on yawning, chewing, swallowingMalleus: has Manubrium, attached to TM, head attached to wall, process attached to incusStapes: footplate attached by annular lig to oval windowTensor tympani: pulls Manubrium medially, decr vibration of TMStapedius: pulls footplate out of OWLabyrinth: inner ear; bony in petrous temporal bone; membranous surrounded by perilymph, filled with endolymph (do not communicate)Cochlea: basilar membrane and Reissner’s membrane divide into 3 chambers (scalae); scala vestibule upper, scala tympani lower, scala media inbetween; contain perilymph; communicate at helicotrema; scala vestibule ends at OW; scala tympani ends at round window closed by 2Y TMOrgan of Corti: on basilar membrane; contain hair cells which are auditory receptors which pierce reticular lamina supported by rods of Corti; arranged in outer and inner hair cell rows; covered by tectorial membrane in which tips of outer hair cells are embedded; nerves go to spiral ganglion in modiolus in core around which cochlea wound form auditory division of VIIIBasilar membrane permeable to perilymph in scala tympani, so hair cells bathed in perilymphSemicircular canals: orientated in 3 planes; membranous canals suspended in perilymph; crista ampullaris located in ampulla of each canal, made of hair cells and sustentacular cells; hair cells in contact with vestibular division of VIIIUtricle: contains macula on floor; contain sustentacular cells and hair cells in which are embedded otoliths; nerve cells join vestibular division of VIIISaccule: contains macula in semivertical position; as above

Hair Cells

Sensory receptors of ear throughout membranous labyrinth embedded in epithelium made of supporting/sustentacular cells, basal end in contact with afferent neurons; apical end has rod like processes (hairs, stereocilia composed of actin) and one true cilium kinociliumMP -60mV; when stereocilia pushed toward kinocilium MP decr to -50mV, when pushed away hyperpolarizes; if pushed in direction perpendicular to this, no change in MP; intermediate produces intermediate de/hyperpolarisation; so shows change in directionTip links tie tip of stereocilia to side of its higher neighbour – when short stereocilia pushed towards taller one, opens channels K and Ca enter channel from endolymph depolarization release of NT depolarization of neuron; K enters sustentacular cells reaches cochlea secreted back into endolymphBases of hair cells bathed in perilymph (formed from plasma), tips in endolymph (formed in scala media by stria vascularis (via N-K-ATPase and K channels), high conc of K, low conc of Na)In Organ of Corti – for hearingIn utricle – for horizontal accelerationIn sacculus – for vertical acceleration3 in semicircular canals – for rotational acceleration

Central Pathways

Auditory pathway: afferent dorsal and ventral cochlear nuclei inf colliculi for auditory reflexes medial geniculate body auditory cortex in Brodmann’s area 41

Most neurons respond to inputs from both ears; several auditory association areas reticular formation

Also efferent olivocochlear bundle which arises from auditory nerve and end around bases of hair cells in Organ of Corti

Vestibular pathway:Afferent in cristae and macula vestibular nucleus and flocculonodular lobe of cerebellumAfferent in semicircular canals vestibular nucleus (sup and med division) nuclei controlling eye movementAfferent in utricle and saccule Deiter’s nucleus (lat division) spinal cord, cerebellum, reticular formationAlso input to thalamus and 1Y somatosensory cortex

Hearing: NOT DONE

VESTIBULAR FUNCTION

Rotational acceleration in semicircular canals stimulates crista endolymph displaced in opp direction to that of rotation fluid pushes cupula bends hair cells; when continuous rotation fluid spins at same rate, cupula returns to normal deceleration displaces fluid in same direction as rotation cupula moves again 25-30 secs to settle; note endolymph displaced toward ampulla on one side of head, and away on other side, so can detect direction as well as rotation via pattern of impulses to brain; linear acceleration doesn’t stimulateVestibular nuclei – maintain position of head in spaceCN nuclei – eye movementsCaloric stimulation – convection currents in endolymph on change in temp nystagmus, vertigo, N

Linear acceleration: urticle (horizontal) and saccule (vertical) respond; also discharge tonically in absence of movement due to gravity reflex righting of head, postural adjustments; some go to cortex for conscious perception of motion and orientation in space (also need proproception, touch and pressure receptors, visual info). Vertigo when labyrinthe inflamed.

Nystagmus: reflex to maintain fixation on stationary objects while body rotates

Vestibulo-ocular reflex: eyes slowly move to maintain visual fixation at beginning of rotation (impulses from labyrinths) snap back to another fixation point (trigger by brainstem) slow movement again; can be horizontal, vertical or rotational (quick component in same direction as rotation, postrotatory nystagmus opp direction)Motion sickness: xs vestibular stimulation reflexes in brainstem and flocculonodular lobe of cerebellum

Smell and taste: NOT DONEBehaviour, sleep: NOT DONE

CONTROL OF POSTURE AND MOVEMENT

Movement:

1) Reflexive – eg. Reflexes (inc. swallowing, chewing, scratching, walking which can have voluntary adjustment)2) Voluntary – performance improves with repetition (synaptic plasticity)

a) Idea

b) Cortical association areas – where commands originate

c) Planned – cortexbasal ganglia and lat cerebellum

d) Via thalamus

e) Premotor and motor cortex make commandsM1 = motor cortex: in precentral gyrus, feet at top, face at bottom; face represented bilaterally; prox limbs ant edge of gyrus, distal limbs post edge; 30% corticospinal/bulbar from hereSupplementary motor area – above cingulated sulcus on med side of hemisphere; projects to motor cortex; involved in programming motor sequences, involved in complex activitiesPremotor cortex – on lat surface; 30% cotricospinal/bulbar from here; projects to cortex and brainstem; involved in postural control40% corticospinal/bulbar come from parietal lobe (esp somatic sensory area)

f) Tracts to motor neurons in brainstem (corticobulbar) and SC (corticospinal)Collaterals end on brainstem nuclei motor neurons in brainstem and SCDamage to corticospinal tract ALONE doesn’t cause spasticity

Lat corticospinal – crosses midline at medulla (80%); skilled movement; destruction loss of pincer grip, wrist movement affectedAnt corticospinal – crosses midline at levels of SC (20%); destruction difficulty with balance, walking, climbing

fibres end on interneurons that contact motor neurons bilaterally

In brainstem: medial/ventral pathways for control of trunk and prox limbs (gross movements) Lateral pathways for control of distal limbs (fine movements)

In CS tracts: ventral/medial pathways (tectospinal, reticulospinal, vestibulospinal) for prox muscles and posture

lateral pathways (rubrospinal) for distal limbs

g) Change in sensory input feedback info motor cortex spinocerebellum brainstem (rubrospinal, reticulospinal, tectospinal,

vestibulospinal)

Pyramidal system = CS tract as if forms pyramids in medulla

Extrapyramidal system = other descending brainstem and spinal pathways; for posture

Somatic sensory area and portions of post parietal lobe project to premotor area; lesions of SSA inability to perform learned tasks

Spinal Cord and Posture

Reflex Stimulus Response Receptor Intergrated InStretch Stretch Muscle contraction Muscle spindles SC, medulla+ive supporting reaction Contact with sole/palm Foot extended Proprioceptors in distal flexors SC-ive supporting reaction Stretch Release of +ive Proprioceptors in extensors SC

Spinal cord: reflex responses; affected by variation of threshold of spinal stretch reflexes, due to change in excitability of motor neurons and change of rate of discharge of efferents to muscle spindles

Lesion: period of spinal shock (reflexes depressed, RMP 2-6mV greater than normal; length of time proportionate to degree of encephalisation of motor function) reflexes return after 2/52(first is flexion of leg flexors and adductors to noxious stimuli / knee jerk) become hyperactive (reflexes released from central control and may be accentuated ie. Removal of inhibition, dennervation hypersensitivity to mediators released by excitatory endings, sprouting of collaterals causing additional excitatory endings) as threshold steadily drops (minor stimuli causes prolonged flexion-extension patterns, eg. Positive supporting reaction when put finger on sole of foot; may be assoc with pain if transaction incomplete)- Negative N balance, catabolise body proteinm ulcers, incr Ca; glucocorticoids decr inflamm response

Pattern generators: in SC, in neck and lumbar; causes walking; turned on by discharge from mesencephalic locomotor region so must be incomplete transactionBladder function: reflex contractions occurBP: baroreceptor reflexes disturbed; wide swings in BPSex: can still get erection of minimal stimulationMass reflex: afferent stimuli radiate from one reflex centre to another; may even radiate to other autonomic centres (eg. urination, sweating, altered BP)

Static reflexes:Phasic reflexes: short term, dynamic

Medulla in Posture (decerebrate)

Tonic labyrinthine reflexes Gravity Contraction of limb extensors Otolithic organs MedullaTonic neck reflexes Head turning

To side

UpDown

Extension of limbs on side to which head turnedHind legs flexForelegs flex

Neck proprioceptors Medulla

Lesion Decerebrate rigidity: Due to lesions in brainstem; spasticity due to diffuse facilitation of stretch reflexes; spastic extensor muscles (uncovers static postural reflex, not affected by phasic postural reflexes, able to stand)

Due to incr excitability of motor neuron pool incr rate of discharge of γ efferent neurons incr spindle sensitivity

1) Incr facilitation: reticular facilitatory area (discharges spontaneously, always functions), vestibular nuclei, some descending pathways (in ant funiculus of SC; have direction action on α motor neurons to incr excitability)

2) Decr facilitation: motor cortex, basal ganglia, cerebellum, reticular inhibitory area (driven by fibres from cortex and cerebellum so if brainstem transected from higher control, ceases to function)

Facilitatory area sends impulses through lat funiculus of SC; damage causes balance to shift to facilitation spasticity

Midbrain in Posture

Labyrinthine righting reflexes

Gravity Head kept level Otolithic organs Midbrain

Neck righting reflexes Stretch of neck muscles Righting thorax, shoulders, pelvis Muscle spindles MidbrainBody on head righting reflexes

P on side of body Righting of head Exteroceptors Midbrain

Body on body righting reflexes

P on side of body Righting of body Exteroceptors Midbrain

Lesion extensor rigidity only present when lying on back (affected by phasic postural reflexes); can rise to standing, walk and right themselves

Righting reflexes: maintain normal standing and keep head uprightGrasp reflex: if above thalamus removed and laid on side, limbs near ground extended, other arm flexed and hand grasps any object brought near itOther midbrain reflexes: pupillary light reflex, nystagmus; vestibular pacing reaction (if lowered quickly forelegs extend and toes spread)

Cortex in Posture (decorticate)

Optical righting reflexes Vision Righting of head Eyes CortexPlacing reactions Visual, exteroceptive,

proprioceptiveFoot places on supporting surface Various Cortex

Hopping reactions Lat displacement when standing

Hops Muscle spindles Cortex

Reflexes intact if no cortex; normal temp regulation etc… Inability to react in terms of past experience

Lesion Decorticate rigidity: due to loss of fibres which inhibit γ efferent discharge via reticular formation (poss at ant edge of precentral gyrus – suppressor strip, 4s); spastic flexion only at rest (affected by phasic postural reflexes)

Basal Ganglia in Posture

High 02 consumption, high copper content

1) Caudate nucleus: cognitive processes2) Putamen3) Globus pallidus: divided into internal and external segments4) Subthalamic nucleus (body of Luys)5) Substantia nigra: divided into pars compacta and pars reticulata

Striatum = 1) and 2); made up of patches/striosomes composed of nerve endings in a matrixReceives afferent connections –

Corticostriate projection from layer 5 of cortex patches layers 2+3 matrix

A projection from thalamus Lenticular nucleus = 2) and 3)

Projections: Substantia nigra striatum globus pallidus subthalamic nucleus globus pallidus and substantia nigra; projections that end on patches dopaminergic neurons in pars compacta of SN; end on matrix GABAergic neurons in pars reticulate of SN

Pathways: Nigrostriatal dopaminergic system – inhibitory to putamen stimulate D1 (which inhibit internal segment of GP) and inhibit D2 (which inhibits int segment of GP) – balance maintains normal function; affected in Parkinson’s (loss of dopaminergic input to putamen decr inhibition, incr excitation of subthalamic nuclei and int segment of GP); symptoms when 60-80% lost), normally lost with age

Intrastriatal cholinergic system – excitatory; affected in HC GABAergic system from striatum to globus pallidus and substantia nigra – inhibitory; affected

in HC; loss of inhibition hyperkinesia

Output: From cortex striatum internal segment of globus pallidus inhibitory to thalamic fasciculus thalamus (ventral lat, ventral ant, centromedian nuclei) excitatory to prefrontal and premotor cortex LOOPFrom substantia nigra thalamusAlso to habenula and sup colliculus

Function: involved in planning and programming movement; role in cognitive processes; involved in speech. Can result in hypo/hyperkinetic state (eg. Chorea, athetosis, ballism, akinesia, bradykinesia)Eg. Huntington’s disease – jerky movement, chorea, slurred speech; autosomal dominant (short arm C4); caused by trinucleotide repeat expansion; onset 30-50yrs; protein huntingtin involvedEg. Parkinson’s disease – also occurs with meds that block D2 receptors; hypokinetic and hyperkinetic (lead pipe rigidity (agonists and antagonists affected), cogwheel rigidity and tremor) aspects, decr associated movements (eg. Swinging arms when walking, facial expression); trt with decr cholinergic system or give L-dopa; proteins α-synuclein and barkin involved

Cerebellum in Movement

Connected to brainstem by sup/mid/inf peduncles; medial vermis and lat hemispheres; large SA; divided into 3 parts by 2 transverse fissures; consists of 10 lobules

Lesion hypotonia, ataxia (incoordination due to errors in rate, range, force, direction of mvmt); compensation will occur if only cortex affected, permanent if nuclei; scanning speech; past-pointing; intention tremor (inability to correct); rebound phenomenon; adiadochokinesia; decomposition of movement

Function: flucculonodular lobe/vestibulocerebellum – nodulus in vermis, flocculus in hemispheres; equilibrium and learning-induced changes in VOR; lesion staggering, broad base

spinocerebellum – rest of vermis and medial hemispheres; receives proprioceptive info from body and ‘plan’ from cerebral cortex; smooths and coordinates mvmts; vermis for axial and prox limb, hemisphere for distal limb

cerebrocerebellum/neocerebellum – lat hemispheres; plan and program mvmts also: learned adjustments that make coordination easier as brain activity shifts from prefrontal area to parietal and motor cortex and cerebellum; via olivary nuclei input via climbing

fibre

External cerebellar cortex:3 layers: external molecular, Purkinje cell, internal granular layersContains Purkinje cells (only output from cerebral cortex, pass to deep nuclei)

Granule cells (also found in cerebral cortex, innervate Purkinje cells)Granule cells have bodies in granular layer send axon to molecular layer bifurcates to form a T branches run parallely (parallel fibres) and synapse with dendrites of Purkinje cells by forming grid

Basket cells (inhibitory; in molecular layer; input from parallel fibres; project to Purkinje cells)

Stellate cells (inhibitory; similar to basket but superficial) Golgi cells (inhibitory; in granular layer axons project to molecular layer and granule

cells; and have input from parallel fibres and Purkinje cells)All use GABA (acting on GABAa receptors) except granule cells, which use glutamate

Separated from white matter by deep cerebellar nuclei:1) Dentate nucleus: neo2) Globose nucleus: spino3) Emboliform nucleus: spino4) Fastigial nucleus: spino

Interpositus nucleus = 2) + 3)

Input: Climbing fibres – excitatory; come from inferior olivary nuclei (which receives proprioceptive input from body); strong excitatory effect on dendrites of Purkinje cell; 1 climbing fibre has 2000-3000 synapses on Purkinje cells

Mossy fibres – excitatory; provide proprioceptive info from body and info from cerebral cortex via

pontine nucleus; weak excitatory effect on dendrites of granule cells in groupings called glomeruli excitatory effect on Purkinje cells; each Purkinje cell has input from 250000-1000000 mossy fibres

Circuit: Climbing and mossy fibres excite Purkinje cells and granule cells Granule cells excite basket and stellate cells via parallel fibres basket and stellate cells inhibit Purkinje cells (feed-forward inhibition)

Mossy fibre and Purkinje collaterals and parallel fibres excite Golgi cells inhibit transmission from mossy fibres to granule cells

Purkinje cells inhibit deep cerebellar nucleiClimbing and mossy fibres excite deep cerebellar nuclei

Output: from deep cerebellar nuclei; always excitatoryvestibulocerebellum brainstemNeocerebellum and spinocerebellum nuclei brainstem (neo also to thalamus)

Autonomic NS: not doneCentral regulation of visceral function: not done

TEMPERATURE REGULATION

Speed of chemical reactions and enzyme systems have narrow temp rangesPoikilothermic: cold-blooded; large fluctuations in tempHomeothermic: warm-blooded; reflex responses from hypothalamus maintain temp in narrow range (36.3 – 37.1); scrotum 32; oral 0.5 lower than rectal; core has circadian fluctuation of 0.5-0.7; lowest at 6am, highest in evenings; raise during time of ovulation; 0.5 higher in children; incr to 40 during exercise

Heat production: exercise, assimilation of food, BMR; incr by E and NE (fast) and thyroid (slow), incr during sym discharge; brown fat is source of heat in infantsHeat loss: radiation (transfer of heat by infrared electromagnetic radiation, not in contact; altered by colour

of clothing; important in lower temps) conduction (exchange between objects in contact; transfer is α temp difference – thermal

gradient – temp of skin determines how much heat is transferred, altered by vasoD/C, rate at which heat transferred from deep tissues to skin = tissue conductance; horripilation – erection of hairs, insulated and decreases heat loss; aided by convection – movement of molecules away from area of contact)

vaporization of water on skin and m membranes of resp tract (vaporization of 1g H20 removes

0.6kcal of heat; insensible loss 50mL/h (1600ml/h during exercise); degree to which sweat vaporizes depends on humidity; can vary from 30-900kcal/h; panting incr loss; important in higher temps)

urine, poo

Temp-regulating mechanisms: reflex responses to cold (threshold 36.8 for vasoC, 36 for non-shivering thermogenesis, 35.5 for shivering) controlled by post hypothalamus, to heat (threshold 37 for sweating and vasoD) controlled by ant hypothalamus; receives afferents from sensory receptors in skin, deep tissue, SC, brainIncr heat loss – cut vasoD, sweating, incr RRDecr heat prod – anorexia, apathy, inertiaDecr heat loss – cut vaso C, curling up (decr body SA), horripilation, countercurrent exchanges (in animals

living in cold H20, heat transferred from arteries to venae comitantes, extremities remain cold, conserve heat)

Incr heat prod – shivering (involuntary), hunger, incr voluntary activity (semivoluntary), incr NE + E (when cut BV’s cold, have incr response to NE+E)

Fever: thermostat reset to point >37 receptors indicate temp is <new set point heat production (if in cold enviro), decr heat loss (if in warm enviro)Endotoxin / inflamm / pyrogenic stimuli monocytes, macrophages, Kupffer cells cytokines (act as endogenous pyrogens; act on OVLT – a circumventricular organ) activate preoptic area of hypothalamus release of PG’s (eg. PGE2) incr temp set point fever (inhibits growth of MO’s, incr ab production; >41 can cause brain damage, >43 causes heat stroke)

Malignant hyperthermia: mutations in gene coding for ryanodine receptor XS Ca release during muscle contraction during stress contractures, incr metabolism incr heat

Hypothermia: slow HR, slow RR, decr BP, decr LOC; ability to spontaneously return to temp to N lost <28

Neural basis of instinctual behaviour and emotions: not doneConditioned reflexes, learning and related phenomena: not done

CARDIOVASCULAR SYSTEM

Electrical Activity of Heart

Pacemaker Potentials

1) Pacemaker potential (prepotential) slowly increases until 2) Action potential triggered3) At peak efflux of K (IK) begins repolarisation 4) IK decay: K efflux decreases, membrane begins to depolarize prepotential develops again

5) Transient Ca channels open complete prepotential; may also be Ca sparks (local release of Ca from SR) contributing to this6) Long-lasting Ca channels open causes AP

Vagal stimulation hyperpolarized membrane, slope decreasesAch M2 receptors G protein response open K channels incr K conductance so longer

for Ik decay decr cAMP slowed opening of Ca channels

Sym stimulation incr r of spontaneous dischargeNE β1 receptors incr intracellular cAMP opens L channels more rapid depolarisation

NB. AP’s due to Ca with no contribution from Na (so no rapid depolarizing spike)NB. There are latent pacemakers in other parts of heart that have prepotentials and take over when SAN goes pear-shaped. A and V muscle only discharge spontaneously when injured/abnormal.

Spread of Excitation

Conduction system composed of modified cardiac muscle (fewer striations, indistinct boundaries); RMP of -90mV; act as syncytium due to gap junctions

SAN: located at junction of SVC and RA; contains P cells (small round cells with few organelles connected by gap junctions); receives mainly R vagus nerve (endocardial fibres) and R sym innervation (from stellate ganglion, epicardial fibres); conduction speed 0.05m/s

3 bundles that connect SAN and AVN; anterior internodal tract of Bachman, middle internodal tract of Wenckebach, post internodal tract of Thorel; slower conduction through atrial myocytes; conduction speed 1m/s; conduction speed 1m/s

AVN: located in R post interatrial septum; only conducting pathway between A and V due to fibrous ring; contains P cells (small round cells with few organelles connected by gap junctions); receives mainly L vagus nerve (endocardial fibres) and L sym innervation (from stellate ganglion, epicardial fibres); conduction speed 0.05m/s

Atrial depolarization complete in 0.1s (AV nodal delay), before excitation spreads to V’sDelay shortened by SNS, lengthened by PNS

Bundle of His: LBB at top of IV septum (later splits into ant and post fascicle) then continues as RBBBranches and fascicles run subendocardially down either side of septum, coming into contact with Purkinje system whose fibres spread to whole V; conduction speed 1m/s BOH, 4m/s Purkinje system

Ventricular depolarization complete in 0.08-0.1s; starts from L IV septum to R across septum down spetum to apex along V walls to AV groove from endocardium to epicardium finally to posterobasal portion of LV, pul conus, and upper portion of septum

ECG

Create equilateral (Einthoven’s) triangle with electrodes on both arms and L leg; measure potential difference between 2 electrodes deflection on paper

Bipolar leads: use 2 active electrodes; standard limb leads (I, II, III) record differences in potential between 2 limbs; deflection here indicates magnitude and direction in axis of electromotive force produced by heart (cardiac axis) and can be calculated if heart is at centre of Einthoven’s triangle can calculate mean QRS vector by estimating net differences between QRS +ive and –ive peaks (normal is -30 to +110 deg)

Lead I: electrodes on RA and LA; LA positive (upward deflection when LA +ive compared to R)Lead II: electrodes on RA and LL; leg positiveLead III: electrodes on LA and LL; leg positive

Unipolar leads: use 1 active electrode and 1 indifferent electrode

6 chest leads: V1-V63 limb leads: aVR, aVL, aVF; augmented as measure between one limb and TWO other limbs

P wave = atrial depolQRS = V depolST and T wave = V repolU wave = slow repolarisation of papillary muscles

Note: atria located posteriorly V form base and ant surface RV is antlat to LV

DRAW CHEST DIAGRAM AND EXPLAIN LEADS

Using ECG, phonocardiogram and carotid pulse can work outQS2 (total electromechanical systole): period from onset of QRS to closure of AV (S2)PEP (pre-ejection period): diff between QS2 and LVEP; time for electrical and mechanical events that precede systolic ejectionLVEP (LV ejection time): fro beginning of caroitid pressure rise to dicrotic notchPEP:LVEP = normal is 0.35; incr due to poor LV performance

Echos: use 2.25MHz frequency

His Bundle Electrogram: catheter places through vein to R heart close to tricuspid valve

Cardiac Arrhythmias

Sinus arrhythmia: accelerates during inspiration, decelerates during expiration; due to fluctuations of paraS input – impulses from vagal nerves from stretch receptors in lung inhibit cardioinhibitory area in medulla oblongata decr vagal input incr HR on inspiration

Sick sinus syndrome: marked bradycardia

1st deg HB: PR long

2nd deg HB: not all A impulses conducted to V2:1, 3:1Wenckebach phenomenon: PR lengthens until misses beat

Complete heart block: when conduction from AV completely interrupted due to AV nodal block / infranodal block (due to septal MI, surgery) V beat at slow r (idioventricular rhythm) independent of A

AV nodal block, AVN takes over as pacemaker (45bpm)Infranodal, V pacemakers (35bpm)

Cerebral ischaemia Stokes-Adams syndrome (faints and dizziness)

L ant hemiblock: L axis deviationL post hemiblock: R axis deviation

Increased automaticity: when other myocardial fibres discharge spontaneouslyEctopic beats: from ectopic focus; if repetitive may paroxysmal tachycardia/A flutter

Reentry: defect in conduction that permits wave of excitation to propogate continuously in closed circuit (circus movement); if reentry in AVN depolarizes A echo beat, if goes down to V paroxysmal nodal tachycardia; may have abnormal bundle of conducting tissue connecting A and V (bundle of Kent), passes in one direction through AVN then the other through bundle can involve both A+V

Atrial ectopic: abnormal P wave but normal QRST; may depolarize SAN which must repolarise then reach firing level before can fire again pause before next beat; cause reseting of normal rhythm

Atrial tachycardia: regular discharge of atrial focus / reentrant activity; in atrial flutter large counterclockwise circus movement in RA sawtooth pattern due to atrial contractions, usually assoc with

A = when AVN activatedH = transmission through His bundleV = V depol

PA interval = time from 1st appearance of atrial depolarization to A wave = conduction time from SAN to AVNAH interval = AVN conduction timeHV interval = from start of H to start of QRS = conduction in BOH and BB’s

AV blocks as AVN can’t conduct >230bpm; in AF, due to circulating reentrant excitation waves in both atria, AVN discharges at irregular intervals V beat at irregular rate (80-160)

Ventricular ectopics: bizarre QRS due to slow spread of impulse from focus through V muscle; can’t excite BOH so retrograde conduction of A doesn’t occur; normal SAN depolarizes atria but P wave hidden in QRS, if it reaches V they will still be in repolarisation phase; however next SAN impulse produces normal beat after compensatory pause (longer than pause from atrial ectopic)

Ventricular tachycardia: due to circus movement in V’sVF: rapid discharge from multiple V ectopic foci / circus movement; can be produced by electric shock / extrasystole during vulnerable period (midportion of T wave, when some of V myocardium depolarized and some incompletely repolarised, some completely repolarised)

Accelerated AV conduction (WPW syndrome): bundle of Kent is aberrant muscular/nodal tissue connection between A+V which conducts more rapidly than AVN 1V excited early short PR and slurred QRS deflection, with normal PJ interval; tachycardias often follow atrial premature beat which conducts down AVN then sprads to aberrant bundle and back up to A circus movement (or vice versa less often)Lown-Ganong-Levine syndrome: short PR but normal QRS; depolarization down aberrant pathway but enter IV conducting system distal to node

Other ECG Changes

MI:MP of infarcted area greater than in normal area current flows from +ive infarct into -ive normal area flows toward electrodes over injured area ST elevationST elevation 1) MP of infarcted area greater than in normal area current flows from infarct into normal

area flows toward electrodes over injured area ST elevation 2) Rapid repolarisation due accelerated opening of K channels ST segment elevation,

within secs, lasting few mins 3) Decr RMP due to K loss current flow into infarct during V diastole TQ segment

depression (looks like ST elevation); within mins 4) Delayed depolarization again infracted area +ive comparied to normal ST segment

elevation; within 30minsNormalisation of ST segment over days/weeks Dead muscle becomes electrically silent so becomes –ive relative to normal myocardium during systole and doesn’t contribute to positivity of complexes Q wave development, incr size of Q wave; failure of progression of R wave; may get BBB if septum involvedVentricular arrhythmias occur during 1st 30 mins (due to reentry) after 12hrs (due to incr automaticity) after 3/7 to several wks (due to reentry)Infarcts affecting epicardium interrupt sym nerve fibres dennervation supersensitivity to NE+E in area beyond infarct; endocardial infarct lesions affect vagal fibres

Hyponatraemia: low voltage complexesHyperkalaemia: peaked T waves (altered repolarisation) prolonged QRS, paralysis of atria V arrhythmia; decr RMP fibres become unexcitable heart stops in diastoleHypokalaemia: prolonged PR, prominent U waves, late T wave inversion; if T and U waves merge, apparent prolonged QTHypercalcaemia: stops in systole (Ca rigor)Hypocalcaemia: prolonged STPhenothiazines, tricyclic antidepressants: prolonged ST

The Heart As A Pump

Pericardial sac contains 5-30ml clear fluidCardiac muscle contracts faster when incr HR; duration of systole fomr 0.16-0.27s; duration of diastole from 0.14-0.62; cannot be tetanised as will not contrat until near end of another contraction due to

prolonged refractory period (theoretical max HR 400; AVN will not conduct faster than 230 so higher HR only seen in V tachy

Contraction starts just after depolarization and lasts until 50ms ater repolarisation is completed; atrial systole starts after P wave; V systole starts near end of R wave and ends just after T wave

Jugular Venous Pulse: shows atrial p changes; decr during inspiration due to –ive intrathoracic pa wave: atrial systole due to regurg of blood into veins and stopping of venous inflow; in CHB will be asynchronous a waves with giant a waves (cannon wave) when A contract against close TVc wave: rise in Ap due to bulging of TV into A during isovolumetric V contraction; giant c wave in tricuspid insufficiencyv wave: incr Ap before TV opens during diastolez: drop in Ap during ejection phase of V as MV and TV pulled downward

Heart Sounds:S1: lub; closure of MV and TV at start of V systole; 0.15s long, low fS2: dup; closure of AV and PV after end of V systole; 0.12s long, higher f; loud and sharp when incr diastolic p in aorta/pul artS3: 1/3 way through diastole due to rapid V filling and inrush of blood; 0.1s longS4: just before S1; if high Ap or stiff V (eg. LVH)

Arterial pulse:

Late diastole: MV and TV open; AV and PV closed; MV and TV drift closed towards end blood flows into A and V (70% of V filling); r of filling decr as V’s become distended

End-diastolic V vol = 130mlAtrial systole: R systole occurs before L

MV and TV open propels more blood (30%) into V via incr Ap contraction of atrial muscle around IVC, SVC and pul veins but still some regurg into veins a wave in JVPVentricular systole: L systole occurs before R (but ejection in R occurs 1st as pul art p<aorta p) MV and TV close isovolumetric ventricular contraction (little shortening of fibres but sharp incr IVp; lasting 0.05s until p in V’s > p in aorta (80mmHg) and pul art (10mmHg))

AV and PV open; AV valves bulge into atria causing small rise in IAp c wave in JVP ventricular ejection (rapid then slow ejection; IVp (L @ 120mmHg, R @ 25mmHg) reaches max then decr so late in systole Ap > Vp but momentum keeps blood going; contraction causes MV and TV to be pulled down causing decr Ap; 70-90ml ejected per V overall)

End-systolic V vol = 50ml EF (% end-diastolic vol ejected per stroke) = 65%; reflects V function

Early diastole: protodiastole (when V muscle fully contracted and Vp drops; 0.04s) Ends when momentum of blood overcome

AV and PV close (during expiration occurs @ same time, during inspiration AV closes before PV due to lower impedance of pul vasc tree) isovolumetric ventricular relaxation (IVp drops rapidly; blood enters A causing incr Ap v wave on JVP) Ends when Vp < Ap

MV and TV open V’s fill rapidly then slower, causing decr Ap

Rate at which wave travels is independent of and greater than velocity of blood flow (4m/s in aorta, 8m/s in large arteries, 16m/s in small arteries – moves faster in older people); pulse in radial artery felt 0.1s after peak systolic ejectionStrength of pulse: determined by pulse pressure; not affected by MAP

STRONG: large SV incompetent AV (may be so strong than head nods with heartbeat; collapsing / Corrigan / water-hammer pulse)WEAK: shock

Dicrotic notch: oscillation in falling phase of pulse wave when aortic valve shuts; not palpable

Cardiac Output

SV: amount of blood pumped by each V in 1 HB = 70mlCO: output per unit time; ave 5L/min; controlled by SV (inotropic) and HR (chonotropic)Cardiac index: output per min per square metre body surface; ave 3.2LPreload: degree to which myocardium is stretched before it contractsAfterload: resistance against which blood is expelled

Measure with:Doppler and echoDirect Fick Method: only applies when arterial blood is only source of substance being taken up; measure amount of O2 used by body in period and divide by AV difference across lungs; use ABG and pul art blood from cardiac catheter

Fick principle: Amount of substance taken up by organ per unit time = (arterial level of substance – venous level (A-V difference)) X blood flowCO = O2 consumption (mL/min) / [AO2] – [VO2]

Indicator dilution method: dye/radioactive isotope (which must stay in blood stream; can use cold saline injected into RA and measure temp change in pul art - thermodilution technique) injected into vein and conc in arterial blood determined serially

CO = amount injected / av. arterial conc after single circ through heart

Starling’s Law of Heart

Energy of contraction proportional to initial length of cardiac muscle fibre (in heart, this is proportionate to end-diastolic vol – SV/EDV = Frank-Starling curve): when stretched tension incr to max then declines

Heterometric regulation: change in CO due to muscle fibre lengthHomometric regulation: change in CO due to contractility

EDV: affected by intrapericardial p (incr V cannot fill) V stiffness (incr by eg. MI) VR (incr by incr blood vol, venoconstriction, decr intrathoracic p, muscular activity,

lying down)Contractility: SNS shifts length-tension curve up and left; NE+E work on β1 receptors and Gs adenylyl

cyclase, incr cAMP Small incr contractility with incr HR Postextrasystolic potentiation – V extrasystole makes succeeding contraction stronger due to

incr availability of intracellular Ca Depressed by incr CO2, decr O2, acidosis, quinidine, procainamide, barbs Intrinsic depression in CCF, ? cause

NB. Athletes have lower HR, greater end-systolic V vol, greater SV @ rest

O2 Consumption of HeartDetermined by: intramyocardial tension, contractile state, HR; correlates with V work (= SV x MAP in pul art or aorta; approx 7x higher for LV as aortic p higher) – for unknown reason incr MAP has bigger effect in workload than incr vol (ie. afterload has bigger effect than preload; ie. AS will be greater problem than regurg)Basal: 2ml/100g/min (higher than resting skeletal muscle)Beating: 9ml/100g/minExtracts most O2 from blood so incr O2 must be provided by incr coronary blood flow

NB. Law of Laplace: tension of wall of hollow viscus proportionate to radius of viscus stretch myocardial fibres incr SVNB. Incr HR incr velocity and strength of contraction BUT decr end-systolic vol and hence radius of heart

Dynamics of Blood and Lymph Flow

Move blood forward: heart pump, diastolic recoil of arteries, compression of veins by skeletal muscle, negative pressure of thorax

Blood VesselsIn vessels: SM innervated by noradrenegeric fibres constriction, cholinergic fibres dilationArtery arteriole metarterioles (may be connected to venule via thoroughfare vessel) capillaries (openings surrounded on upstream side by precapillary sphincters (not innervated, but respond to local vasoconstrictors; when dilated RBC can pass in single file in thimble shape)

Arteries: 0.4cm diameter, 1mm wall thickness, 20cm2 cross-sectional area, 8% blood Outer layer adventitia (CT), middle layer media (SM), inner layer intima (endothelium – secretes

growth regulators, vasoactive substances - and CT) Large amount elastic tissue in inner and outer layers recoil during diastole

Resistance vessels: principle site of PVR

Arterioles: 30μm diameter, 20μm wall thickness, 400cm2 cross-sectional area, 1% blood Less elastic tissue, more SM Major site of PVR

2% blood in aorta

Capillaries: 5μm diameter at arterial end, 9μm diameter at venous end, 1μm wall thickness (single layer of endothelial cells); 4500m2 cross-sectional area, 5% blood; typical p is 32mmHg at arteriolar end, 15mmHg at venous end; pulse p 5mmHg at arteriolar end, 0 at venous end; blood travels at 0.07cm/s; transit time is 1-2secs; 24L fluid filtered per dayJunctions between cells permit passage of molecules <10nm diameter (tighter in brain)Vesicular transport in cells via endo- then exocytosis of plasma and proteinsFenestrations: in endocrine/intestinal villi/kidneys; cytoplasm attenuated to form gaps; 20-100nm

diameter closed by thin discontinuous membrane which permit passage of large molecules; no membrane in glomerulus and sinusoids of liver; in sinusoids gaps 600-3000nm diameter

Fluid movement = k (related to permeability of capillary and area of filtration[(HPG) – (OPG)]Diffusion important for exchange of nutrients and waste materials; filtration also important, depends on balance of Starling forces (eg. hydrostatic pressure gradient and osmotic pressure gradient)

HPG = HP in capillary – HP in interstitial fluid (directed outward)OPG = OP in plasma – OP of interstitial fluid (directed inward)

Fluid moves into interstitium at arteriolar end (filtration > oncotic p), into capillary at venous end (oncotic p > filtration)If fluid reaches equilibrium in tissue diffn can be increased by incr flow (flow-limited)If doesn’t, diffn is diffusion-limitedPericytes: outside endothelial cells; long contractile processes wrap around vessels and react to

local vasoactive agents to regulate flow esp in inflammIn resting tissues, most capillaries collapsed and bypassed via thoroughfare vessels; in active tissues metarterioles and precapillary sphincters dilateNoxious stimulus release of substance P, bradykinin and histamine incr cap permeability

AV anastomoses (shunts): in fingers, palms, earlobes; have thick, muscular walls; abundant innervation

Venules: 20μm diameter; 2μm wall thickness; 4000cm2 cross sectional area

Veins: 0.5cm diameter; 0.5mm wall thickness (thin and easily distended); 40cm2 cross sectional area; pressure 12-18mmHg (5mmHg in gt veins; 4.6mmHg is CVP as enters RA); affected by gravity; velocity incr as blood enters larger veins

Little SM but capable of much venoconstriction from noradrenergic nerves and circulating vasoC Intima folded to form venous valves (not in small veins, great veins, brain, viscera) Capacitance vessels: can ake large amount of blood before incr venous p Flow encouraged by negative intrathoracic p on inspiration (falls to -6 from -2.5mmHg decr CVP

to 2 from 6mmHg aids VR; also diaphragm produces +ive intraabdo p pushes blood into thorax) and muscle pump

Muscle pump, also pulsations of arteries near veins Gravity causes pooling decr CO Veins above heart collapse, but dural sinuses don’t as rigid walls so have p that is subatmospheric

Veins and venules contain 54% blood12% blood in heart cavitiesVeins + pul circ + RA, LA, RV = low pressure systemLV + arterial system = high pressure system

Smooth muscle: contains Ca, K and Cl channels; contraction by myosin light-chain and latch-bridge mechanismInflux of Ca through voltage-gated channels

incr cytosolic Ca contraction Ca release from SR via ryanodine receptors Ca sparks incr activity of Ca-activated K

channels (big K/BK channels) incr K effluex incr MP closed voltage gated Ca channels relaxation; important in control of vascular tone

Angiogenesis: in embryo development network of leaky capillaries formed from angioblasts (vasculogenesis) vessels hook up with capillaries which give then SM maturation; vascular endothelial GF (VEGF) important, also involved in lymphangiogenesis

Blood Flow

Flow = Effective perfusion pressure / ResistanceFlow = vol per unit time (cm3/s)Flow and resistance markedly affected by small changes in caliber of vesselsFlow x2 by 19% incr radiusLaminar flow: infinitely thin layer of blood in contact with wall doesn’t move next layer has low velocity flow fastest in centre of streamOccurs up to critical velocity – higher than this causes turbulent flow; probability of this related to diameter of vessel (more turbulent with smaller diameter) and viscosity of blood (more turbulent with decr viscosity eg. anaemia)Measuring blood flow: electromagnetic flow metres, Doppler flow metres, adaptations of Fick and indicator dilution techniques, plethysmographyShear Stress: flow blood creates force on endothelium that is parallel to long axis of vessel; change in shear stress change in genes in endothelial cells related to CV function produce integrins, GF’s etc…

Shear stress (γ) = viscosity (η) X shear rate (rate at which velocity increases from vessel wall toward lumen)

Windkessel effect: recoil during diastole of stretched vessels during systole (ie. elastic) forward flowAir embolism: forward movement of blood depends on blood being incompressible; air compressible so if enters heart can stop heart; bubbles lodge in small vessels and markedly incr resistance to flow

Effective perfusion p = mean intraluminal p @ arterial end – mean p @ venous endPulse pressure = systolic – diastolic p = normal is 50mmHg; incr with incr ageMean pressure = diastolic p + 1/3 pulse pressure; av p throughout cardiac cycle; systole shorter than diastole so slightly lessCritical closing pressure: when p in small BV decreased to < tissue p no blood flows and vessel collapses (even tho p is not 0)Pressure falls rapidly in small arteries/arterioles as high resistance to flow; p at arterioles 30-38mmHg (pulse p 5mmHg)Pressure incr below heart level, decr above heart level

Resistance (in R units) = pressure (mmHg) / flow (ml/s)Also determined by radius of BV’s (vascular hindrance), viscosity of blood (plasma 1.8x more viscous than water, blood 3-4x more viscous than water depending on hematocrit; hematocrit has greater effect on viscosity in larger vessels due to difference of nature of flow in small vessels; must be v large incr viscosity to have effevt on PVR; decr viscosity incr blood flow)

Velocity = displacement per unit time (cm/s) = flow / area of conduit

Average velocity: incr area incr velocity; high in aorta, decr in arteries, incr in veins, high in IVC (but lower than aorta); measure by injecting bile salt in arm and measuring time til bitter taste; ave arm-to-tongue circulation time = 15secsMean velocity in prox portion of aorta = 40cm/s (from –ive value in diastole to 120 during systole)

Law of Laplace: tension in wall = (transmural p x radius of vessel) / wall thickness Transmural p = pressure inside – pressure outside

Protects small diameter vessels from rupture – the smaller then vessel the lower the tension needed to balance transmural p; in dilated heart large radius, so greater tension must be developed to produce any given pressure dilated heart must do more work

Measuring BPAuscultatory method: using Riva-Rocci cuff attached to sphygmomanometer; use sounds of Korotkoff; in hyperthyroidism, children, aortic insufficiency and after exercise diastolic is sound when muffles, not disappears; constriction causes critical velocity to be exceeded; tapping due to turbulent flow at peak of systole which is staccato; then as approached diastolic turbulent flow becomes more continuous so becomes muffled; artificially high in fat people as some cuff pressure dissipated so use wider cuff; if left inflated too long reflex vasoC falsly incr BP; auscultatory gap when sound disappear above diastolic then return, may accidentally get low BPPalpation method: 2-5mmHg lower than auscultatory method

Lymphatics Normal flow in 24hrs = 2-4L; return protein to bloodCapillary efflux > influx extra fluid enters lymphatics (prevents incr IFp) enter R and L subclavian veins at junction with IJV; contain valves; regular LN’s; no fenestrations, little basal lamina, open junction between endothelial cells with no tight intercellular connections2 types: initial lymphatics: no valves or SM; found in intestine and skeletal muscle; fluid enters through

loose junctions between endothelial cells. Drain into…collecting lymphatics: have valves and SM which have peristalsis, aided by skeletal muscle pump, negative intrathoracic p during insp, high velocity blood flow in veins in which lymph terminates

Lymphagogues: incr lymph flow

Incr interstitial fluid vol and oedema:Incr filtration p – arteriolar dilatation

venular constrictionincr venous p (CCF, incompetent valves, venous obstruction, incr total ECF vol due to salt and water retention (eg. cirrhosis, nephrosis), gravity)

Decr osmotic p gradient across capillary – decr plasma protein level (eg. cirrhosis, nephrosis) accum of osmotically active substance in interstitial

spaceIncr cap permeability – substance O, histamine, kinins etc…

Also depends on: capillary p, IFp, capillary filtration coefficient, no. active capillaries, lymph flow, ratio of precap to postcp venular resistance (precap constriction lower filtration p, postcap incr)In active tissues incr cap pressure osmotically active particles can’t enter capillaries as osmotic p overcome accumulation affect osmotic gradient so fluid leaves capillaries incr lymph flow, but still incr vol in musclesLymphoedema: high protein content lymph fluid accumulates chronic inflamm condition fibrosis of interstitial tissue elephantitis

Cardiovascular Regulatory Mechanisms

Central Control

BP controlled by vasomotor centre in MOExcitatory: CO2, hypoxia

cortex via hypoT (emotion, sexual excitement) pain pathways via reticular formation and exercising muscles (pressor response to stim of somatic afferent nerves is somtatosympathetic reflex) carotid and aortic (in carotid and aortic bodies) chemoreceptors – discharge causes production of Mayer waves (slow regular oscillations in arterial p); carotid body glossopharyngeal, aortic body vagus stimulation vasoC and bradycardia

however hypoxia inc RR, incr E+NE release from adrenal medulla incr HR, BP, COhypercapnia stimulates vasomotor area but CO2 is vasoD so no vasoCincr ICP compromised blood supply to vasomotor centre local hypoxia and hypercapnia incr discharge Cushing reflex incr BP, decr HR (due to

baroreceptor reflex)Inhibitory: cortex via hypoT inflation of lungs carotid (small dilation of ICA just above bifurcation of CCA, in carotid sinus) + aortic (in wall of AoA in aortic arch, monitor arterial circ) and cardiopul (in walls of atria – type A discharges mainly during A systole, type B mainly late in diastole during peak A filling; type B discharge incr when VR incr) baroreceptors resembling Golgi tendon organs located in adventitia of vessels – stimulated by distension incr discharge r afferent fibres via glossophargyngeal (for carotid) and vagus (for aortic) nerves (buffer nerves) to MO nucleus of tractus solitarius secrete glutamate to stimulated GABA-secreting inhibitory neurons and vagal motor neurons

incr PNS, decr SNS vasoD, decr BP, decr HR, decr CO, incr renin (retain H20); reach max discharge at 150mmHg but linear increase with BP til then; respond to sustained p, change in p and pulse p incr release of vasopressin

In chronic incr BP ‘reset’ to maintain incr BP

Bainbridge reflex: rapid infusion of blood/saline incr HR if initial HR slowCoronary chemoreflex / Bezold-Jarisch reflex: injections of serotonin/veratridine/capsaicin into CA supplying LV cause apnea followed by rapid breathing, hypotension and bradycardiaPulmonary chemoreflex: injections of drugs into PA cause same effectValsalva manouvre: incr BP due to incr intrathoracic p added to p of blood in aorta decr BP as incr intrathoracic p causes decr VR and CO decr pp and MAP inhibit baroreceptors incr HR and PVR stop manouvre CO restored but still incr PVR so incr BP stimulate baroreceptors decr HR; will fail to show these responses in autonomic insufficiency; still have responses in sympathectomy as still have vagal tone intactLV stretch receptors may play a role in vagal tone

SNS cell bodies in rostral ventrolateral medulla sym preganglionic neurons in interomediolateral gray column of SC secrete excitatory NT glutamatePNS dorsal motor nucleus of vagus and nucleus ambiguous

Mechanisms for Regulation

1) Alter output of heartSNS +ive chonotropic effect and inotropic effect; inhibit vagal stimulation; mod sym tone (tonic discharge)PNS -ive chonotropic effect; high vagal tone (tonic discharge)

2) Change diameter of resistance vessels: 1) Autoregulation: compensate for changes in perfusion pressure; esp good in kidneys

Intrinsic contractile response of SM to stretch (myogenic theory of autoregulation) Law of Laplace: wall tension proportionate to distending p X radius of vessel

2) Locally produced vasoD metabolites – accumulate in active tissues (metabolic theory of autoreg); decr blood flow (decr O2 tension, decr pH, incr CO2 – esp important in skin and brain, incr osmolality) causes accum relaxation of arterioles and precapillary sphincters

eg. K (important in skeletal muscle); lactate; adenosine (in cardiac muscle)

3) Substances secretes by endothelium Serotonin released from platelets in injured arteries sticks to vessel wall vasoCProstacyclin from endothelial cells: inhibits plt aggregation and causes vasoDThromboxane A2 from plts: promotes plt aggregation and vasoC

together localize plt aggregation and clot formation; shifted towards prostacyclin by aspirin (inhibits COX decr TA2 and prostacyclin, but endothelial cells can create new

TA2 in hours but new plts need to be formed in 4 days)NO (endothelium-derived relaxing factor, EDRF): made from arginine, catalysed by NO synthase (NOS1 in NS, NOS2 in macrophages and other immune cells, NOS3 in endothelial cells; 1+3 activated by agents that incr intracellular Ca inc Ach and bradykinin; 2 activated by cytokines); when flow to tissue incr by arteriolar dilation, large arteries to tissue also dilate – mediated by NO; products of plt aggregation cause NO release to keep blood flow patent; tonic release of NO needed for normal BP; involved in angiogenesis

activates guanylyl cyclase cGMP vasoDEndothelin-1: made from prohormone big endothelin-1 endothelin via endothelin- converting enzyme; secreted into media of BV’s, act in paracrine fashion; stimulators (AII, NE+E, GF’s, hypoxia, insulin, HDL, shear stress, thrombin), inhibitors (NO, ANP, PGE2, prostacyclin); incr circulating conc in CCF and after MI; endothelin-1 in brain, kidneys and endothelial cells; endothelin-2 in kidneys and intestine; endothelin-3 in blood, brain, kidneys, GI tract; play role in regulating passage across BBB, decr GFR in kidneys G protein coupled receptor phospholipase C vasoCKinins – bradykinin (precursor high-molecular-weight kininogen) lysylbradykinin (kallidin, can be converted to bradykinin; precursor low-molecular-weight kininogen) Act on B1 (pain producing effects) and B2 receptors Proteases (kallikreins – plasma kallikrein circulates in inactive form, tissue kallikrein located on apical membranes of cells) release BK and LBK) Inactive kallikrein (prekallikrein) converted to active form by active factor XII (CF XII and kallikrein exert +ive feedback; HMWK activates CF XII) both metabolized to inactive fragments by kininase I and II (which is same as ACE)

contraction of visceral SM; relax vascular SM via NO; incr capillary permeability, chemotaxis; responsible for incr blood flow when glands are secreting products

CO produces by heme, catalysed by HO2 vasoD

4) Circulating vasoactive substances: VasoD: Adrenomedullin (AM) – inhibits aldosterone secretion, incr production NO, inhibit peri SNS

action; found in plasma, tissues, adrenal medulla, kidney, brain ANP – secreted by heart; antagonizes vasoC substances VIP, histamine, substance P, E in skeletal muscle and liverVasoC: vasopressin – causes little change in BP NE – generalized effect; circulating levels unimportant, more effecting when released from nerves E – other than skeletal muscle and liver AII – generalized effect; also causes incr H20 intake and stimulates aldosterone secretion Urotensin-II – in cardiac and vascular tissue, very potent

AVP, Na-K ATPase inhibitor, neuropeptide Y

5) Nerves: resistance vessels more densely innervated than capacitance (except splanchnic)Noradrenergic vasoC (resistance and capacitance not necessarily the same), all over body; have tonic activity (lack of activity vasoD); may also contain neuropeptide YSympathetic vasodilator system: cholinergic sym vasoD fibres of which postganglionic neurons to BV’s in skeletal muscle secrete Ach vasoD in skeletal muscle to run through thoroughfare channelsCholingergic vasoD; in skeletal muscel, heart, lungs, kidneys, uterus; travel with sym fibres; no tonic activity; may also contain VIPForm plexus on adventitia of arterioles fibres extend to media and end on outer surface of SM transmitters diffuse into media and current spreads through gap junctionsNB. Afferent impulses from sensory nerves in skin relayed down branches to blood vessels release substance P vasoD and incr cap permeability (axon reflex)

6) Incr temp in active tissues vasoD

3) Alter amount of blood pooled in capacitance vessels: circulating vasoactive substances, nerves

Venocontriction incr VR shift blood to arterial side of circulation

Circulation Through Special Regions

Fick principle: blood flow of organ = amount of substance removed from blood stream by organ in unit time / (conc of substance in arterial blood) – (conc substance in venous blood)

Cerebral Circulation Ave blood flow is 54ml/100g/min (756ml/min to brain; 69ml/100g/min to gray matter, 28 to white matter)

In carotids more important than vertebrals; little crossing over from contralateral side, anastomotic channels don’t permit much flow and insufficient to prevent infarction; capillaries surrounded by endfeet of astrocytes close to basal lamina with gaps of 20nm between endfeet; total blood flow remains relatively constant – autoregulation important and keeps arterial p at 65-140mmHgKety method: uses Fick principle using inhaled N2O; measures flow to perfused areas of brain only, gives ave blood flow to brainMeasuring blood flow to specific parts of brain: use position emission tomography (2-deoxyglucose uptake is good indication of blood flow; can measure concs of dopamine etc…); MRI can image amount of blood in area

Awake: blood in premotor and frontal regionsSequential movements: blood in supplementary motor areaCreative speech: Broca’s and Wernicke’s areaProblem solving, reasoning, motor ideation without movement: premotor and frontal cortexR handed – verbal task L hemisphere, spatial task R hemisphereAlzheimers: decr blood to sup parietal cortex, then temporal then frontalHuntington’s: decr blood to caudate nucleusManic depression: decr blood to cortex when depressedSchizophrenia: decr blood to frontal and temporal lobes and basal ganlgia

Innervation: postganglionic sym neurons (cell bodies in sup cervical ganglia) NE, neuropeptide Y; end on large arteries

cholinergic neurons (from sphenopalatine ganglia) Ach, VIP; end on large arteries sensory nerves (cell bodies in trigeminal ganglia) substance P, neurokinin A, CGRP; end

on more distal arteriesIncr BP incr noradrenergic discharge decr the incr in blood flow and protects BBB; so has effect on autoregulation and p-flow curve shifted to R (greater incr p can occur without incr flow)

Choroid plexus: choroid epithelial cells connected by tight junctionsCSF: CSF vol 150ml, produce 550ml/day, turnover 3.7x per day; lumbar CSFp 70-180mm (112 ave); formation independent of IVp, but absorption is proportionate to IVp (and stops <68 external/communicating hydrocephalus); same composition as brain ECF with free communication; 50-70% formed in choroid plexuses, rest in BV’s along ventricular wall foramen of Magendie and Luschka to SA space absorbed through arachnoid villi (projections of arachnoid membrane and endothelium of sinuses into venous sinuses) which permit bulk flow (500ml/day) of CSF into veins and cerebral venous sinuses, or 50ml/day diffuse into cerebral BV’sFunction: protect brain; brain supported within arachnoid by BV’s and nerve roots and multiple fine arachnoid trabeculae

BBB: maintains constant enviro of neurons in CNS as minor variations have large consequences; immature in neonates kernicterus; tends to breakdown in areas of infection/injury (tumours lack tight junctions, so take up drugs better); capillaries resemble non-fenestrated capillaries in skeletal muscle, but tight junctions between endothelial cells limiting passage of substances; flow greater out of than into brain

Little vesicular transportLimited passive diffusion - easy: water, CO2, O2, lipid-soluble steroid hormones - hard: proteins and polypeptides don’t

- slow: H, HCO3, gluNumerous carrier mediated and AT systems

Glu: GLUT1 55k in capillaries; major source of E; 55mg/100g/min = 77mg/min total; insulin not required from brain cells to use gluNa-K-2Cl cotransporter (stimulated by ET-1 and 3): leeps brain K conc lowTranporters for thyroid hormones, choline, nucleic acid precursors, aa’sMultidrug non-specific transporter P-glycoprotein: transport OUT drugs that diffuse IN to brain

Diffusion easy: water, CO2, O2, lipid-soluble steroid hormonesDiffusion hard: proteins and polypeptides don’t; slow penetration of H and HCO3

Outside BBB (circumventricular organs): have fenestrated capillaries therefore are permeable; may function as neurohemal organs (substances secreted enter circulation); may act as chemoreceptor zone – circulating substances change brain function

Posterior pituitary and median eminence of hypothalamus – neurohemal organArea postrema – chemoreceptor zone, initiates vomiting in response to chemical changesOrganum vasculosum of lamina terminalis – mediate H20 intake; site of osmoreceptor controlling vasopressin secretion; fever produced by IL-1

Subfornical organ – mediate H20 intake

ICP: brain (1400g) + SC + spinal fluid (75ml) + blood (75ml) + cerebral vessels, which are relatively incompressible, in rigid bony box – vol must remain constant (Monro-Kellie doctrine) – cerebral vessels compressed when ICP rises, incr venous p decreases cerebral blood flow

eg. body accelerated upwards (positive g) blood moves towards feet decr venous p and ICP in head less p on arteries blood flow less severely compromises; may cause vision loss and LOC @ over 5geg. body accelerated down (negative g) raise ICP and arterial p at head vessels supported and don’t rupture; may cause congestion of head and neck vessels, ecchymoses around eyes, severe throbbing headache and confusion

Cerebral metabolic rate for O2: 3.5ml/100g/min (49ml/min for brain) = 20% total body resting O2 consumption; brainstem more resistant to hypoxia; basal ganglia, thalamus and inf colliculus esp susceptibleAmmonia removal: glutamate taken up by brain takes up ammonia leaves as glutamine; ischaemia can decr glutamate uptake

Coronary Circulation Coronary flow at rest = 250ml.min (5% CO)Extracts 70-80% O2 – can incr only by incr blood flow

CA coronary sinus / ant cardiac veins / arteriosinusoidal vessels (connect arterioles to chambers) / thebesian veins (connect capillaries to chambers) / arterioluminal vessels (small arteries draining into chambers) / some anastomoses between coronary arterioles and extracardiac arterioles

Measuring flow: use Kety method by inserting catheter into coronary sinus; can injected radionucleotides and determine their uptake into myocardial cells by Na-K ATPase which is proportionate to blood flow / selectively uptaken by damaged cells

Flow: Diastole shorter when incr HR so decr LV CA blood flow during tachycardia Flow in subendocardial portion of LV in diastole therefore prone to ischaemic damage and aortic

stenosis (as higher LV systolic p needed to eject so CA’s severely compressed) Flow in more superficial portions throughout cardiac cycle as systolic force is dissipated Decr blood flow if decr aortic diastolic p Decr blood flow if incr venous p as decr effective coronary perfusion p

Chemical factors: decr O2, incr CO2/H/K/lactate/PG/adenine nucleotides/adenosine, occlusion of artery then release (reactive hyperemia) vasoD; adenosine helps to decr reperfusion injury

Neural factors: α-receptors mediate vasoC; β-receptors mediate vasoD; NE causes incr HR and contractility incr release of vasoD metabolites vasoD, but direct effect theoretically is vasoC; vagal vasoDAngina: due to ‘P factor’; irreversible changes in muscle; note lipoprotein(a) interferes with fibrinolysis by down-regulating plasmin generation; homocysteine damages endothelial cells; inflammatory process involved

Splanchnic Circulation Liver and viscera receive 30% of CO via celiac/sup mesenteric/inf mesenteric arteries (vasoC decreases portal inflow; in severe shock may get hepatic necrosis)

Intestine: higher blood flow to mucosa; much anastomoses

Hepatic: Liver receives 1000ml/min from portal vein, and 500ml/min from hepatic artery (mean p = 90mmHg; walls innervated by SNS via hepatic sym plexus vasoC diverts blood from liver); no vasoD nerve fibres to liver; 25-30% vol of liver is blood so contraction of capacitance vessels causes much blood to enter arterial circ

Intestines/pancreas/spleen portal vein (portal venous p = 10mmHg; walls innervated by SNS via splanchnic nerves

asoC when decr BP raised portal pressure and brisk passage of blood through liver bypassing most; dilates due to passive mechanism when incr BP incr blood flow)

through acinus of liver (zone 1 well oxygenated, zone 3 poorly; p in sinusoids lower than in portal vein; large gaps between endothelial cells in walls of hepatic sinusoids, highly permeable)

terminal branches of hepatic vein (hepatic venous p = 5mmHg) at periphery IVC

There is inverse relationship between hepatic arterial and portal venous blood flow – as portal flow decr, accum of adenosine causes dilation of arterioles

Spleen: SNS contraction discharge pool of blood into circulation

Cutaneous Circulation Blood flow can vary rom 1-150ml/100g/min

Fingers, toes, palms, earlobes contain anastomotic connections between arterioles and venules vary blood flow; cold blue skin = arterioles constricted, capillaries dilated; warm red skin = arterioles and capillaries dilatedSNS, E+NE cut vasoC; painful stimuli incr SNS output cut vasoCNo known vasoD nerve fibres to skin; vasoD due to decr SNS tone and local vasoD substancesExercise cut vasoD despite incr SNS due to incr hypothalamuc temp; shock is more profound if incr temp

White reaction: pressure contraction of precapillary sphincters so blood frains out; lasts 15secs

Triple response: present in total sympathectomy; due to axon reflex (C fibres centrally release substance P)Firm pressure 1) red reaction (due to capillary dilation) after 10secs 2) local swelling (wheal, local oedema due to incr permeability of cap

and post-cap venules) 3) diffuse reddening (flare, due to arteriolar dilation) – absent in LA skin and sensory

denervation; present after nerve block

Reactive hyperemia: incr blood to region when circ re-established after period of occlusion; vasoD occurs due to hypoxia during occlusion then filled when occlusion relieved

Placental and Fetal Circulation

Uterus: incr blood flow during pregnancy; oestrogens incr blood flowPlacenta: villi containing fetal umbilical artery and vein branches project into placenta which is large blood sinus; exchange less efficient than in lungs as villi layers thicker and less permeable than alveoliFetal circulation: 55% fetal CO passes through placenta; L+R heart pump together due to PFO and PDARA foramen ovale LA LV aorta / RV ductus arteriosus aorta

umbilical arteries to placenta (60% saturated with O2) placenta umbilical vein (80% saturated with O2) from placenta

ductus venosus IVC (mixed blood 67% saturated with O2) RA portal blood of fetus (26% saturated with oxygen) IVC RA

Most blood from SVC enters RV pul artery ductus arteriosus as resistance in lungs high so pul art p > aortic p@ birth: incr PVR, gasps causing negative intrathoracic p causing expansion of lungs aortic p > pul art p (decr to 20% of in utero p) incr p in LA PFO closes PDA constricts within hours thought to be due to arterial O2 tension

Fetal respiration: fetal cells have greater affinity for O2 (HbF) than maternal cells (HbA); fetus has good resistance to hypoxia

Cardiovascular Homeostasis in Health and Disease

Gravity Effects greater when decr blood volPostural hypotension in sympatholytic drugs, diabetes/syphilis damaging SNS, 1Y autonomic failure, abnormal baroreceptor reflexes in 1Y hyperaldosteronismIn feet: MAP = 180-200mmHg, venous p = 85-90mmHg; if don’t move 300-500ml pool in capacitance vessels of legs oedema, decr SVIn head: MAP = 60-75mmHg, venous p = 0

Stand up decr BP in baroreceptors incr HR, maintain CO; incr renin and aldosterone; arteriole constrict

MAP in head drops by 20-40mmHg, JVP drops 5-8mmHg so less drop in perfusion p (MAP-VP); ICp decr so less vascular resistance as less p on cerebral vessels

more O2 taken from each unit of blood muscle pump needed on prolonged standing to maintain VR

Blood flow decr by only 20% on standing; effects multiplied by acceleration0 gravity atrophy of mechanisms that usually maintain normal CO postural hypotensionSpace motion sickness: headward shift of body fluids loss of plasma vol, diuresis; loss of muscle mass and bone minerals (incr Ca excretion), loss of red cell mass, altered plasma lymphocytes

Exercise Resting skeletal muscle blood flow = 2-4ml/100g/minContraction compression of blood vessels if >10% tension; total stop of blood flow if >70% tension; however between contraction massive incr blood flow so overall 30x more; impulses in sym vasoD system and decr SNS tonicity may be involved

Local mechanisms: Hypoxia, hypercapnia, accum of K (esp important in early exercise) and vasoD metabolites, incr T dilation of arterioles and precapillary sphincters (10-100x incr in open capillaries)

incr area of vascular bed, decr velocity of flow, incr cap p > oncotic p, accum of osmotically active metabolites faster than can be taken away decr osmotic grad across cap walls fluid transudation into ISF and incr lymph flow

Decr pH and incr T shift dissociation curve of Hb to R more O2 given up from bloodIncr 2,3-DPG decr affinity of Hb for O2

Anaerobic metabolism: uses glu; muscle incurs O2 debt

Systemic mechanisms:

Isometric muscle contraction incr HR and BP due to decr vagal tone (little change in SV); likely due to psychic stimuli acting on MO; decr blood flow to muscles due to compression of BV’sIsotonic muscle contraction incr HR (max HR decr with age, in adults rarely >195) and SV and CO, decr PVR due to vasoD in exercising muscles; only mod incr in SBP, unchanged or decr DBP; incr VR due to muscle and thoracic pump, mobilization of blood from viscera (may incr arterial blood by 30%), incr p from dilated arterioles on veins, venoconstriction; after exercise BP may become subnormal due to continued local vasoD

Temp regulation: lost through skin, resp, vaporization of sweat, dilation of cut vessels (inhibition of SNS tone)

Trained athletes: decr HR, incr SV, incr max O2 consumption possible (related to max CO and max O2 extraction by tissues), incr mitochondria, enzymes, capillaries in skeletal muscle less lactate production; improved production of NO and prostracyclin by CA’s

InflammInflammation: localized response to foreign substances; involves cytokines, neutrophils, adhesion molecules, complement, IgG, PAF, monocytes, lymphocytes; arterioles dilate, cap incr permeability; nuclear factor-κB plays important role (cytokines/viruses/oxidants activate it binds DNA icnr production and secretion of inflammatory mediators; activation inhibited by glucocorticoids)Systemic response: cytokines acute phase proteins (proteins in which levels change by 25% following injury) eg. CRP, serum amyloid A, haptoglobin, fibrinogen, albumin, transferring

Wound healingTissue damage plts adhere to exposed matrix via integrins that bind collagen and laminin

plt aggregation and granule release encouraged by thrombin granules inflamm response

selectins attract WBC bind to integrins on endothelial cells extravasation through BV walls

WCC and plt release cytokines up-regulate intergrins on macrophages migrate to injury

fibroblasts and epithelial cells mediate wound healing and scar formation

plasmin removes excess fibrin aids migration of keratinocytes into wound to restore epithelium under scab

collagen proliferation scar

Shock Inadequate tissue perfusion and CO

Hypovolaemic shock: inadequate fluid; haemorrhage, trauma (may get rhabdo, accum of myoglobin in kidneys clogging tubules), surgery, burns (more plasma loss so haemoconcentration; haemolytic anaemia, inc BMR), vomiting, diarrhoeaEffects: Decr VR decr CO (if mod pp decr but MAP normal) and inadequate perfusion

anaerobic metabolism lactic acidosis depress myocardium and peri vascular responsiveness to NE+ELoss of RBC decr O2 carrying capacity

low BP, incr HR, thready pulse, cold pale clammy skin, thirst, incr RRCompensatory mechanisms:1) Baroreceptors less stretched incr SNS

incr HR vasoC (spare brain and heart; marked in skin, kidneys (afferent<efferent decr GFR; Na and nitrogenous retention uraemia and ARF) and viscera shifting blood into arterial reservoir) venoC (incr VR)

2) Incr catecholamines (adrenal medullary secretion incr E; NE due to incr activity of SNS) generalized vasoC

stimulation of reticular formation restlessness incr RR and motor pump incr VR3) Stimulation of chemoreceptors (hypoxia, acidosis, anaemia)

incr RR vasomotor centre of MO vasoC

4) Renin AII thirst, vasoC, incr aldosterone retention of H20

5) Incr vasopressin retention of H20 6) Decr capillary p fluid enters caps from ISFLong term mechanisms: plasma vol restored within 12-72hrs but mostly protein free dilute plasma protein cells (replaced over 3-4days by albumin influx and incr production), decr haematocrit after several hrs (increases again over 4-8/52); incr 2,3-BPG in RBC Hb easily releases O2Refractory shock: when shock persists for hrs progresses to state when vasopressor drugs/replacement of blood vol will not help and CO remains depressed; severe cerebral ischaemia depression of vasomotor and cardiac areas of brain vasoD and decr HR; decr CA blood flow myocardial failure; may get ARDS

Distributive/vasogenic/low-resistance shock: vasoD increases size of vascular system; fainting/neurogenic (eg. postural, micturition - bradycardia, carotid sinus, - decr HR and vasoD, deglutination, cough – incr ITp decr VR, effort – esp in aortic/pul stenosis, anaphylaxis (large amount histamine released), sepsis (usually G-ive bacteria; distributive and hypovolaemic; caused by endotoxins, cytokine and coagulant reactions MOF), neurocardiogenic (arrhythmia, heart block, sinus arrest); skin warm

Cardiogenic shock: inadequate pumping of heart; MI (usually LV), CCF, arrhythmias; shock plus congestion of lungs and viscera

Obstructive shock: obstruction of blood flow in lungs/heart; tension pneumothorax, PE, cardiac tumour, cardiac tamponade

Hypertension Sustained elevation of systemic arterial pPressure = flow x resistance (viscosity of blood and caliber of resistance vessels)

Long-term incr BP LVH, incr O2 consumption of heartEssential hypertension: no cause knownRenal hypertension: caused by compromised renal blood supplyCoarctation of aorta: incr renin secretion and PVRPheochromocytomas: secrete E+NEPill hypertension: oestrogens incr angiotensinogen secretionMonogenic hypertension: mutations of genesMalignant hypertension: necrotic arteriolar lesions develop papilleodea, cerebral symptoms, progressive renal failure

Heart Failure Heart unable to pump enough blood adequate for needsSystolic failure: decr SV as V contraction is weak incr ESVV, decr EF cardiac remodeling and LVH, incr secretion renin and aldosterone Na and H20 retention; finally get LVDDiastolic failure: EF initially maintained but elasticity reduced so filling reduced ends up with same results as aboveHigh-out failure: normal CO but still not enough to reach needs (eg. thyrotoxicosis, thiamine def)

RESPIRATORY PHYSIOLOGY

C = concV = vol

Structure and Function

Function: Oxygen in, CO2 out; metabolises compounds, filters unwanted materials, reservoir for bloodInspiration: incr thoracic vol air drawn into lung beyond terminal bronchioles SA enormous so forward velocity of gas is small diffusion of gas rapidly, easy settling of dust (large particles filtered out by nose, small particles removed by mucus from mucus glands and goblet cells which is swept up by cilia then swallowed; alveoli have no cilia, particles engulfed by macrophages lympatics/blood)Lower parts of lung ventilate better than higher

Blood-Gas Interface: Simple diffusion of gases – from high to low ppBarrier thin (0.3μm) and has SA 50-100m2 by wrapping capillaries around polyhedral alveoli300 million alveoli in lung (0.33mm diameter, vol 4L)Holes in alveolar walls are pores of KohnV delicate so collapse easily due to surface tension, this is prevented by surfactant which lowers STGas must cross: surfactant, alveolar epithelium, interstitium, capillary endothelium, plasma, erythrocyte wallFick’s law of diffusion: amount of gas across sheet of tissue is proportional to area and inversely proportional to thickness

pp = (conc of gas) X (total p of gas)ppO2 at sea level = 159mmHgppO2 inspired air = 149mmHg

Airways:Conducting portion: trachea L+R main bronchi lobar bronchi segmental bronchi terminal bronchioles; no part in GERespiratory zone: Resp bronchioles (with occasional alveoli on walls) alveolar ducts (lined with alveoli)

Total ventilation = tidal vol x resp frequencyConducting potion = anatomic dead space = 150ml doesn’t reach resp zoneNormal ratio of dead space : tidal = 0.2-0.35 in resting breathingLung distal to terminal bronchiole = acinus = 3000ml alveolar gas @ rest Alveolar ventilation = (500 – 150) x 15 = 5250ml/min fresh air available for GE – incr by increasing tidal vol or resp fAlveolar ventilation = amount fresh gas reaching alveoli = (VT – VD) x n

Measuring anatomic dead space: Increases with deep insp due to traction of bronchi; changes on size and posture; use Fowler’s method – breathing through valve box measure gas at lips, breathing 100% O2, all expired N2 comes from alveolar gas - measure N2 on expiration (rises until plateau when alveolar gas is being expired (alveolar plateau) measure ADS by working out vol expired until plateau reached)

Physiologic Dead Space: vol of gas that doesn’t eliminate CO2; physiological dead space incr in lung disease; Bohr’s method – since all expired CO2 comes from alveolar gas

A = alveolar; E = mixed expiredVT x FE = VA x FA and VT = VA + VD VA = VT – VDtherefore VT x FE = (VT – VD) x FA so VD = FA + FE

VT FApp α conc so Bohr equation = VD = PACO2 – PECO2

VT PACO2

Measuring alveolar ventilation: 1) Measure total ventilation with valve box2) Measure alveolar ventilation = dead space ventilation - total ventilation

T = tidal; D = dead space; A = alveolar; n = resp frequency; V = vol per unit time; VE = expired total ventilation; VD and VA = dead space and alveolar ventilation in tidal volume breathing

VT = VD + VA VT x n = (VD x n) + (VA x n) VE = VD = VA VA = VE – VD

2) Measure conc of CO2 in expired gas – no GE occurs in anatomic dead space so no CO2 in ADS at end of inspiration so all expired CO2 comes from alveolar gas; ppCO2 α fractional conc of gas in alveoli (PC02 = FCO2 x K); PCO2 of alveolar gas and arterial blood same so ABG can be used to show alveolar vent

VCO2 = VA x %CO2 (fractional conc, FCO2) VA = V CO2 x 100 100 %CO2

VA = V CO2 x K PCO2

Measuring Lung VolumesMeasure with spirometer:

Vital capacity (amount of max expiration after max inspiration) = Normal breath (tidal vol) = 500ml

= 7500ml/min total ventilation (RR 15)Air entering lung > leaving lung as more O2 enters than CO2 leaves

Can’t measure with spirometer:

Total lung capacity = Residual vol (gas still in lung after max expiration)Functional residual vol (gas still in lung after normal expiration)

1) Gas dilution technique: breath helium (due to low solubility in blood) from spirometer which equilibrates in lungs without any lost; measures only communicating gas

1 = in machine; 2 = in lung Amount before equilibration of helium = C1 x V1 Amount helium after equilibration = C2 x (V1 +V2) Amount of helium is unchanged so C1 x V1 = C2 x (V1 + V2) V2 = V1 x (C1 – C2)

C2

2) Body plethysmograph: sit in box; breath out shutter closes try to breath in by increasing vol of lung incr p in box; measures all gas in lung inc that in closed airways that doesn’t communicate with mouth; in diseased lungs there is big difference

Boyles law: PV=K at constant pressureP 1 and 2 = pressure in box before and after insp effort; V = vol in boxP3 and 4 = pressure in mouth before and after insp effort; V2 = FRC

P1 x V1 = P2 x (V1 – ΔV)P3 x V2 = P4 x (V2 – ΔV)

Blood vessels:

R heart pul art capillaries pul vein; low resistance; initially art, vein and bronchus run together but in periphery veins pass between lobules, but bronchi and art travel together down centre of lobules dense capillary network (diameter 10μm) in walls of alveoli; each RBC spends 3-4secs in cap network transversing 2-3 alveoli – complete equilibrium occurs in this time; capillaries easily damaged (eg. high cap p, high lung vol) leak plasma and RBC into alveolar spacesConducting system blood supply comes from bronchial circ; v small blood flow compared to above

Pul cap blood = 70ml Pul blood flow = 5000ml/min

Diffusion

Diffusion determined by Fick’s law:Rate of diffusion through tissue slice proportional to area (50-100m2)

inversely proportional to thickness (0.3μm in places)Diffusion rate proportional to partial pressure difference between 2 sides

proportional to solubility of gas in blood-gas barrier inversely proportional to square root of molecular weight

Diffusion limited (eg. CO): RBC enters capillary CO moves from alveolar gas into RBC rapidly CO binds with Hb so little incr in partial pressure so CO can continue to enter RBC’s; not limited by amount of blood available but diffusion properties of blood-gas barrier

Diffusing capacity CO depends on area and thickness of blood-gas barrier vol of blood in pul capillaries alveolar vol

Reaction rate of CO can be altered by high alveolar pO2 as they compete for Hb

Perfusion limited (eg. NO): no combination with Hb incr pp after RBC has travelled only 1/10 along capillary so no further NO transferred; depends on blood flow and not properties of blood-gas barrier

For O2: pO2 in RBC entering capillary = 40mmHg pO2 in alveoli = 100mmHg so passes into RBC; capillary pO2 reaches alveolar pO2 1/3

of way along capillary then transfer becomes PERFUSION LIMITED little diff between alveolar gas and end-capillary blood

O2 combines with Hb in 0.2s (less avidily than CO) some raise in pp, delaying loading of O2 into RBC so increasing ‘overall diffusion distance’

Resistance of uptake of O2 due to reaction rate = resistance due to blood-gas barrier

For CO2: diffusion 20x faster than O2 as has higher solubility, but can still be diff between end-capillary blood and alveolar gas in diseased lung

DM = diffusion membraneθ = rate of reaction of Hb with O2 (in ml per minute of O2 = diffusion capacity of 1ml of bloodVC = vol of capillary blood

1/DL = 1/DM (resistance of blood-gas barrier) + 1/(θ x VC = effective ‘diffusing capacity’ of rate of reaction of Hb with O2

Challenges:Exercise incr pul blood flow RBC usually spends 0.75s in capillary, but decr to 0.25s less time available for oxygenation, but no fall in end-capillary pO2 in normal peopleIf tissue slice thickened poor diffusion doesn’t equilibrate fully even by end of capillary (diffusion limited) diff between alveolar gas and end-capillary bloodLower alvolar pO2 (eg. high altitude) decr pp diff so O2 moves more slowly fails to reach alveolar pO2

Measuring diffusing capacity: Normal = 25ml/min-1/mmHg-1

ie. vol CO transferred per min per mmHg of alveolar ppCO used as uptake is diffusion-limited; note as p capillary blood slow low, can usually be ignored

Vgas (amount gas transferred) = DL (diffusing capacity of lung) x (p alveolar gas – p capillary blood)

Single breath of CO rate of disappearance of CO from alveolar gas during 10sec breathhold calculated by measuring expired CO; incr by 2-3x on exercise

Blood Flow and Metabolism

RV main PA (walls thin with little SM so work of R heart as small as possible) branches accompany airways as far as terminal bronchioles capillary bed around alveolar wall (variable pressure, most p drop occurs here) pul veins running between lobules 4 large pul veins LA

Pul capillaries (alveolar vessels): surrounded by gas in alveoli so collapse/distend depending on alvolear p; pressure around caps decr by surface tension of surfactant; diff between p inside and outside capillaries = transmural pPul arts and veins (extraalveolar vessels): less p surrounding them; as lung expands, pulled open by parenchyma – dependent on lung volV large vessels are outside lung substance and dependent on intrapleural p

Pul Vascular Resistance

Vascular resistance = input p – output p blood flow

Main PA = 15mmHg LA = 5mmHg Difference = 10mmHg (Pul circ)Pul blood flow = 6L/minVascular resistance = (15-5)/6 = 1.7mmHg/L-1/min (low as just for distribution)Any incr pul art/venous p pul vascular resistance falls (ie. on exercise)

Due to recruitment: spare capillaries which under normal conditions are closed/open with no flow, as p rises they begin to conduct; important when high arterial p

distension: widening of capillary segments; important when high vascular pInc resistance at low vol (Extra-alveolar vessels have high resistance when lung vol low causing

high critical opening pressure for pul art regional change in blood flow starting at base where parenchyma less expanded)

high vol (Alveolar vessels – if alveolar p incr compared to capillary p incr resistance (eg. on deep inspiration; calibre of capillaries decr at large lung vol due to stretching of alveolar walls incr resistance)

Incr resistance if hypoxia as causes constriction of small pul arteriesDrugs that cause incr resistance = serotonin, histamine, NE; esp effective when decr lung vol as affect extra-alveolar vessels Drugs that decr resistance = Ach, isoproterenol

Aorta = 100mmHg RA = 2mmHg Difference = 98mmHg (Systemic circ)Higher resistance due to muscular arterioles

Measuring Pul Blood Flow

Using Fick Principle: O2 consumption per minute = amount of O2 taken up by blood in lungs per minute

VO2 = O2 consumption per minute (collect expired gas in spirometer)Q = vol of blood passing through lungs each minuteCaO2 = O2 content in blood leaving lungs (arterial, via ABG)CVO2 = O2 content in blood entering lungs (pul art, via catheter)VO2 = Q (CaO2 – CVO2) Q = VO2

CaO2 – CVO2

Passive Distribution of Blood Flow

In human upright lung blood flow lower at apices – in zone 1 alveolar p > cap p no flow if decr arterial p (eg. severe haemorrhage) or incr alveolar p (eg. PPV). Becomes alveolar dead space as is ventilated but not perfused.Zone 2: below apices; sufficient arterial p but low venous p; blood flow determined by diff between arterial and alveolar p as opposed to the normal arterial/venous p difference (Starling resistor / waterfall effect – when chamber p greater than downstream p, downstream p has no effect on flow so venous p has no effect here)Zone 3: venous p > alveolar p so flow determined by arterial/venous p difference; incr blood flow in this region of lung due to distension of capillaries; transmural p difference increases the further down lung you go as cap p incr but alveolar p is same throughout lungZone 4: region where get decr blood flow at low lung vols due to narrowing of extra-alveolar vessels

Affected by posture (lying increases flow to apices, but doesn’t affect basal flow; incr post flow, decr ant flow) and exercise (upper and lower blood flow increases)

Active Control of CirculationDecr pO2 alveolar gas hypoxic pulmonary vasoconstriction (contraction in hypoxic region; doesn’t need CNS ?due to release of vasoC substance by perivascular tissue ?due to inhibitors of NO ?causes inhibition fo voltage-gated K channels membrane depolarisation incr Ca channels in cytoplasm SM contraction; changes more marked when alveolar pO2 <70mmHg; directs blood away from hypoxic regions of lung decr deleterious effect of lung segment. NB. Occurs in fetusDecr pH also causes vasoC

Water Balance in LungStarling’s law: pushing out of capillary = capillary hydrostatic p – interstitial fluid hydrostatic p pulling into capillary = blood osmotic p – interstital fluid osmotic p

Involved in this is reflection coefficient (σ) – effectiveness of cap wall in preventing passage of proteins across it

Net fluid out = K (filtration co-efficient)[(Pc – Pi) – (πc – πi)]Likely net OUTWARDS push likely into interstitium of alveolar wall then to perivascular (have low p so aid this) and peribronchial space (interstitial oedema) enter lymphatics; in later pul oedema fluid may enter alveolar spaces (poss when max drainage rate exceeded), fluid pumped out by Na-K ATPase in epithelial cells

Other Functions of LungLungs also act as reservoir of blood; filters blood (small thrombi removed); makes vasoactive substances (eg. leukotrienes (airway constriction in asthma) and PG’s (relax PDA in fetus, role in bronchoconstriction in asthma) from arachidonic acid), modifies blood-borne substances (AI AII); inactivates bradykinin, some PG, removes serotonin (uptake and storage), NE; angiotensin II, E and ADH unaffected by lungs; can

secrete IgA into bronchial mucosa; plays role in clotting mechanism; makes dipalmitoyl phosphatidylcholine (in surfactant); protein synthesis

Ventilation-Perfusion Relationships

pO2 inspired air = 149mmHg by time reaches alveoli pO2 = 100mmHg (1/3 decrease)2 contributing processes – removal of O2 by pul capillary blood (governed by O2 consumption of tissues), continual replacement by alveolar ventilation

Alveolar pCO2 = 40mmHg

Causes of Hypoxaemia

Hypoventilation decr alveolar pO2 (unless additional O2 inspired), incr pCO2 (always); fall in alveolar pO2 slightly larger than pCO2Following normal ventilation again, pCO2 will take longer to normalize as CO2 stores greater than O2 stores due to large amount of bicarb in blood

VCO2 = CO2 productionVA = alveolar ventilationR = respiratory exchange ratio or resp quotient (CO2 production / O2 consumption; determined by metabolism of tissues) = 0.8F = correction factorpCO2 = VCO2 x K

VA Alveolar gas equation: PAO2 = PIO2 – PACO2 + F

R

Causes: morphine, barbs, damage to chest wall, paralysis of resp muscles, high resistance to breathing

DiffusionThere is always a pO2 diff between alveolar gas and end-capillary blood due to incomplete diffusion; diff enlarged by exercise, thickened blood-gas barrier, low O2 mixture inhaled

ShuntBlood that enters arterial system without going through ventilated areas of lung (eg. bronchial artery blood entering pul veins, coronary venous blood entering LV, pul AV fistula, VSD) addition of poorly oxygenated blood depressing arterial pO2Hypoxaemia CANNOT be fully abolished by giving 100% O2 as blood still bypasses alveoli will cause incr dissolved O2 in blood as Hb will be saturatedDoesn’t cause hypercapnia as chemoreceptors sense incr pCO2 and incr ventilation decr pCO2 of shunted blood

This equation can be used if shunt caused by mixed venous bloodQT = total blood flowCaO2 = O2 concentration in arterial blood

QT x CaO2 = total amount of O2 leaving system = amount of O2 in shunted blood (Qs x CVO2) + end capillary blood (QT-Qs) x ccO2

(calculated from alveolar pO2 and O2 dissociation curve)So… Qs = CcO2 – CaO2 QT CcO2 – CVO2

Ventilation-Perfusion RateVQ determines GE in any single lung unitIf O2 added at Vgm/min-1 and blood pumped through at Qlitres/min-1 then conc of O2 in alveolar compartment and leaving blood is V/Qgm/L-1Inspired air has pO2 150mmHg, pCO2 0mmHgVenous blood entering unit has pO2 40mmHg, pCO2 45mmHgAddition of pO2 by ventilation and removal by blood flow alveolar pO2 100mmHg, pCO2 40mmHgObstruct ventilation completely O2 and CO2 of alveolar gas and end-capillary blood = mixed venous bloodObstruct blood flow completely alveolar O2 and CO2 will increase until reaches same as inspired gasNote: CO2 may not incr as chemoreceptors stimulate incr RR which will usually make normal pCO2 in arteries (as CO2 dissociation curve almost linear, so incr RR will incr CO2 output by lung units with low and high VQ ratios). Wasted ventilation = ventilation in XS of what would usually require. This may not incr O2 thought due to O2 dissociation curve being nonlinear (so only units with low VQ ratio will benefit from incr RR, some hypoxaemia will still remain though).

Regional Gas ExchangeVentilation: higher at bottom than top, smaller difference

Difference greater in O2 than CO2 (as CO2 more reliant on ventilation than blood flow) resp exchange ratio (CO2 output / O2 uptake) greater in apex than base

Perfusion: higher at bottom than top, more differenceLittle contribution of apex O2 to pH due to poor blood flow thereOn exercise blood flow incr to apex assumes larger share of O2 uptake

Ventilation:perfusion ratio high at top of lung

VQ mismatch: decr O2 uptake, decr CO2 output

High ventilation: perfusion = obstruction to blood (these units are alveolar dead space) depression of arterial pO2 to below alveolar pO2 (alveolar-arterial O2 difference) (high pO2 doesn’t incr O2 conc of blood due to nonlinear shape of O2 dissociation curve; CO2 doesn’t rise in same way as curve is almost linear)Decr CO2 elimination

Low ventilation:perfusion = obstruction to ventilationDecr O2 uptake

Measuring VQInject dissolved inert gas and measure conc in arterial blood and expired gasMeasure alveolar-arterial pO2 difference: arterial pO2 – ‘ideal’ alveolar pO2 (pO2 lung would have if no VQ inequality)

PAO2 (alveolar) = PIO2 (inspired pO2 = 140mmHg) – PACO2 (arterial CO2) + F R (0.8)AA gradient = PAO2 – arterial pO2

Gas Transport By The Blood

Dissolved O2: obeys Henry’s law = amount dissolved proportional to partial pressure1mmHg pO2 = 0.003ml O2/100ml of blood so 100mmHg O2 arterial blood = 0.3mlO2/100ml (3mlO2/L)

Haemoglobin-bound O2: heme (iron –porphyrin compound) joined to globin (4 polypeptide chains, 2 alpha 2 beta); HbA normal, HbF fetal, HbS sickle (valine instead of glutamic acid in beta chains, shift in

dissociation curve to R, deoxygenated form poorly soluble and crystalises in red cell change in shape to crescent, fragile, thrombus formation)Oxygenated state is R (relaxed) stateDeoxygenated state is T (tense) state

O2 dissociation curve: Flat upper portion: if pO2 falls, loading unaffected

as RBC takes up O2, large pp diff between alveolar gas and blood exists even when most O2 transferred

Steep lower portion: peri tissues can withdraw large amounts of O2 with only small drop in capillary pO2 so O2 can easily enter cellsShift to R decr affinity of Hb for O2 (incr H, pCO2, T, 2,3-DPG which is end product of RBC metabolism, may be depleted in stored blood) more offloadingShift to L incr affinity of Hb for O2Effect of pCO2 (due to effect on H conc) is Bohr effect

O2 concentration: (1.39 x Hb x Sat/100) + 0.003pO2

Remember: if pt has Hb 10, their O2 capacity is 20.8 x 10/15 = 13.9ml/100ml; 13.5ml/100ml combined at sats 97.5%. 0.3ml dissolved overall 13.8ml/100ml total O2 conc.

CO interferes by combining with Hb carboxyhaemoglobin; 240x higher affinity for Hb than O2 normal pO2 but much decreased O2 conc; shifts curve to L, interfering with unloading

CO2 dissociation curve:

O2 + Hb HbO2 (oxyhaemoglobin)Amount of O2 bound to Hb increases rapidly until 500mmHg then levels out thereafter

Max amount O2 that can bind Hb is O2 capacity – when all available binding sites occupied – expose blood to v high pO2 and subtract dissolved O21g Hb can bind 1.39ml O2Normal blood has 15g Hb/100ml so capacity 20.8ml/100ml

O2 saturation: % of available binding sites that have O2 attached; 97.5% if 100mmHg O2 (arterial), 75% if 40mmHg (venous)

O2 combined with Hb X 100 O2 capacity

Normal value of pO2 at 50% sat is 27mmHg which is P50

Carbon DioxideLung excretes 10,000mEq carbonic acid per day

1) Dissolved: obeys Henry’s law; 20x more soluble than O2; 10% of CO2 is in dissolved form2) Bicarbonate: contains bulk of CO2 (60%)

a. CO2 + H2O (carbonic anhydrase) H2CO3 H(+) + HCO3(-) (last 2 steps are Henderson-Hasselbalch equation

b. First reaction slow in plasma, fast in RBC due to presence of CAc. Second reaction fastd. When conc of H and HCO3, HCO3 diffuses out but H can’t as membrane is impermeable

Cl ions moves into cell from plasma (chloride shift) in accordance with Gibbs-Donnan equilibrium some bind to reduced Hb as it is less acidic than oxygenated Hb; deoxygenated/reduced Hb helps loading of CO2 (Haldane effect; increases osmolar content of RBC water enters RBC incr vol), while oxygenation in pul capillary assists unloading (cells shrink on passing through lung)

H+ + HbO2 H+Hb + O23) Carbamino compounds: 30%; combination of CO2 with amine groups in blood proteins, esp

globin of Hb carbaminohaemoglobin; rapid reaction, no enzyme; reduced Hb can make HbNHCOOH easier than HbO2; unloading of O2 in peri tissue facilitates binding of CO2 and vice versa

i. HbNH2 + CO2 HbNHCOOH

Acid-Base Status

Henderson-Haselbalch equation gives H2CO3 H+ + HCO3-KA (dissociation constant of carbonic acid) = H+ x HCO3-

H2CO3As H2CO3 conc is proportional to CO2 conc, KA = H+ x HCO3

CO2- log of this is pH: -log (H+) = -log KA + log HCO3/CO2pH = pH = pKA + log HCO3/CO2

As CO2 obeys Henry’s law: pH = pKA (=6.1) + log (HCO2 = 24 in normal blood) / (0.03 x pCO2)

More linear than O2 dissociation curve The lower the sat of Hb with O2, the larger the CO2 conc for given pCO2 (Haldane effect – better ability of reduced Hb to mop up H+ produced when carbonic acid dissociates, greater ability of reduced Hb to form carbaminohaemoglobin

More steep than O2 dissociation curve Between 40-50mmHg CO2 conc changes more that O2 – so pO2 diff between arterial and venous blood is large, but pCO2 diff is small

CO2 curve shifted to R by incr SO2

Metabolic alkalosisIncr ratio HCO2:pCO2 incr pH (AE); resp compensation incr pCO2 decr HCO3:pCO2 (ED) base XS; resp compensation often small and may be absent

Blood-tissue Gas Exchange O2 delivery = CO x arterial O2 concCaused by: low pO2 due to pul disease (hypoxic hypoxia)

decr ability of blood to carry O2 (anaemic hypoxia)decr tissue blood flow (circulatory hypoxia)toxic substance that interfere with ability of tissue to use O2 (histotoxic hypoxia) (eg. cyanide prevents used of O2 by cytochrome oxidase)

O2 and CO2 move from blood into tissue by simple diffusion; thickness 50μm (more than blood-gas barrier); when exercising capillaries open up incr area for diffusion; since CO2 diffuses faster, elimination is OK; if intercapillary distance or consumption O2 incr inadequate tissue perfusion at point in middle between capillaries critical situation when pO2 <3mmHg may get anoxic region where aerobic metabolism not possible anaerobic glycolysis; high cap O2 ensures diffusion of O2 to mitochondria

Mechanics of Breathing

As long as ratio of HCO3 : pCO2 x 0.03 remains 20, pH will remain same; HCO3 detemined by kidney, pCO2 by lung

Davenport diagram: shows relationship between HCO3, pCO2 and pH; A is normal plasma; line CAB (buffer line) is effect as carbonic acid is added to whole blood – presence of Hb makes line steeper, displaced upwards if more HCO3 from kidneys (incr base excess defined by distance between new buffer line and old), vice versa

Respiratory AcidosisIncr pCO2 decr HCO2/pCO2 ratio decr pH move towards B as HCO3 must incr due to dissociation of carbonic acid, but ratio of HCO3:pCO2 decr; if persists, kidney conserves HCO3 and secretes H+ as H2PO4 and NH4 so ratio HCO3:pCO2 returns to normal (moves from B to D compensated resp acidosis which is usually not complete so pH not completely normalized, amount detemined by base XS (vertical difference between BA and DE)

Resp alkalosisDecr pCO2 incr HCO3:pCO2 ratio incr pH (AC); renal compensation excretes HCO3 return ratio to normal (CF) which may be nearly complete base deficit

Metabolic acidosisDecr ratio HCO3:pCO2 decr pH (AG); resp compensation lowering pCO2 incr HCO3:pCO2 due to H+ ions detected by chemoreceptors (GF) base defecit

Muscles of Respiration

Inspiration: diaphragm (supplied by phrenic nerve, C345; in tidal breathing moves 1cm; on forced up to 10cm; paradoxical movement when paralysed, moves up on inspiration)

ex intercostal muscle (bucket-handle lat movement; IC nerves) accessory muscles (scalene, SCM)

Expiration: passive on quiet breathing due to elasticity active needs abdo wall muscles (RA, IO, EO, TA); in intercostals

Elastic Properties

Pressure-Vol curve:

Surface Tension = force acting across imaginary line 1cm long in surface of liquidDue to attractive forces between adjacent molecules of liquid are stronger than between liquid and gas liquid SA becomes as small as poss; aim to form a sphere (smallest SA for given vol) generate p within bubble determined by Laplace’s law: p = (4 x surface tension) / radiusCells lining alveoli secrete surfactant (phospholipids containing DPPC – dipalmitoyl phosphatidylcholine – made for fa’s made by lung or extracted from blood) made by type II alveolar cells which decreases surface tension of alveolar lining fluid; has rapid turnover

DPPC molecules are hydrophobic at one end and hydrophilic at the other when they align intermolecular repulsive forces act decr surface tension; actions more strong in small SA as molecules are closer together so repulsive forces better

Surfactant’s Uses1) Incr compliance of lung decr work required; absences decr compliance2) Incr alveolar stability: there is tendancy for small alveoli to collapse and inflate larger ones; since p generated by surface forces inversely proportional to radius p higher in smaller vol bubble; however surface tension decr in small SA, opposing this; absence atelectasis3) Keep alveoli dry: surface tension tends to suck fluid from capillaries into alveoli due to decr hydrostatic p in tissue; so surfactant prevents transudation; absence pul oedema

Interdependence: since all alveoli are connected, if one bunch collapses tissue exerts expansive forces on them

Regional Differences in VentilationLower regions ventilate better than upper: intrapleural p less –ive at bottom due to weight of lung and +ive p required to support it so basal lung is relatively compressed in resting state and has small resting vol,

P-V curve is non-linear; becomes stiffer at high volsHysteresis: lung vol at any p during deflation is larger than during inflationNote lung without any expanding p still has air inside it; even if p is above atmospheric p (0 on horizontal axis) airways will collapse trapping air inside (this occurs at higher vols in lung disease)p in airways and alveoli = atmospheric; change in pressure occurs outside lung transpulmonary pressure (p outside lung is subatmospheric due to elastic recoil of lungCompliance = slope of p-v curve (ie. vol change per unit p change); compliance is 200ml/cm water; at higher expanding pressuresDecr compliance (slope of curve flattens): lung disease, alveolar oedema, incr pul venous p and if lung unventilated for long period due to atelectasis and incr surface tensionIncr compliance: pul emphysema, normal aging lung, asthma attackElasticity: tendancy of lung to return to resting vol after distension due tp fibres of elastic and collagen in alveolar walls and around vessels and bronchi

but it expands more on inspiration than apex – since ventilation is change in vol per unit resting vol, this area has high ventilation; apex has large expanding p, big resting vol, small change in vol on inspirationAt low lung vols: lung easier to inflate as compliance is high; so at full expiration, intrapleural p’s less –ive intrapleural p at base > airway (atmospheric) p airway closure (air trapping occurs; occurs easier in older lungs due to loss of elastic recoil, so intrapleural p less –ive)) and not ventilated at base during small tidal vols, whereas apex can still ventilated

Uneven VentilationIn normal lung, vol change on insp is large and rapidLow compliance: change in vol is rapid but smallHigh airway resistance: inspiration is slow and not complete before it is time to inhale; so if high RR, will be smaller inspired vol; this unit has a long time constantIncomplete diffusion: if there is dilatation of airways in resp bronchioles, distance to be covered by diffusion increased inspired gas not distributed uniformly

Elastic Properties of Chest WallIf put air into intrapleural space lung collapses, chest wall springs outwardAt FRC: relaxation p of lung and chest wall = atmospheric (ie. inward pul of lung balanced by outward spring of chest wall)Lung retracts at all vols above minimal volChest wall tends to expand at vols up to 75% vital capacity

Airway Resistance P difference between mouth and alveoli Flow rate

Airflow Through TubesIf air flows through tube, diff in p between endsDetermining whether flow will be laminar or turbulent is Reynold’s number which gives ratio of inertial to viscous forces; in straight smooth tubes, turbulent when Re>2000 (wide tube, high velocity) (less likely if low-density gas (eg. helium))

Re = 2rvd (radius, velocity, density) n (viscosity)

Entrance conditions to tube important: if eddy formation occurs at branch point, disturbance will be carried downstream; laminar flow likely to only occur in small terminal bronchioles; in most of tree, flow is transitional; turbulence occurs in trachea

Low flow rate: laminar flow; driving p is proportionate to flow rate (P=KV); Note that radius is more important to resistance than length

In circular tubes: vol flow rate (V) = driving p (P) x π x r 4 8 x viscosity (n) x length (l) Flow resistance = driving p / flow …so R = 8nl πr4

High flow rate: formation of eddies, or even turbulence; has different properties as driving p is proportionate to square of flow r (P=KV2); viscosity of gas less important, but density more important

Pressures During Breathing Cycle

Airway ResistanceMajor site of resistance is medium-sized bronchi; <20% is in small airwaysFactors: Lung vol: as lung vol decreases, airway resistance rises as airways aren’t held open by

parenchyma; at low vols basal segments even closeContraction of bronchial SM: incr resistance; mostly β2 receptors relax SM; paraS causes incr resistance; decr pCO2 in alveolar gas incr resistance due to direct actionDensity and viscosity of gas: incr densitiy incr resistance

Dynamic Compression of AirwaysLimits air flow during forced expiration (when you exhale, flow rises rapidly to high value then decreases over most of expiration) due to compression of airways by intrathoracic pHigh lung vol: rise in intrapleural p (via increasing exp effort), results in greater exp flowMid and low vols: flow becomes independent of effort after certain intrapleural p is exceeded (ie. flow is effort independent)

1) Preinspiration: airway p (flow) is 0, intrapleural p is -5cm; so airway held open by 5cm transmural p

2) During inspiration : intrapleural and alveolar p decr; alveolar p -2cm, airway p -1cm, intrapleural p -7; flow begins; airway still held open by 6cm transmural p

3) End-inspiration : airway p (flow) is 0, intrapleural p is -8cm; airway still held open by 8cm transmural p

4) Forced expiration : intrapleural p and airway p increase; alveolar p 38cm, airway p 19cm, intrapleural p 30cm; p drop along airway, which tends to CLOSE airway (-11cm transmural p)

a. If intrapleural p increased further by muscular effort in attempt to expel gas, effective driving p unaltered (as effective driving p is alveolar – intrapleural p; NOT MOUTH P)

b. Max flow decr with vol as diff between alveolar and intrapleural p decreases and airways become narrower

c. Flow is independent of resistance of airways downstream of point of callapse (equal p point)

d. As exp continues, EPP moves more distally down lung, as resistance of airways rises further as lung vol falls

Shape of intrapleural p curve different to vol curve due to changes in lung compliance

Before inspiration: Intrapleural p = -5cm due to elastic recoil of lungAlveolar p = 0cm (atmospheric); with no airflow there is no p difference along airways

On inspiration:Lung expands elastic recoil increases intrapleural p drops from AB on black line; intrapleural p decreased even more by airway resistance (80%) (hatched area, AB on blue line)Part of hatched area is due to tissue resistance (20%) – p required to overcome viscous forces of tissue as they slide over eachotherTissue + airway resistance = pulmonary resistance

On expiration:Note airway resistance causes intrapleural p to be LESS negative (follow blue line)

May occur easier in diseased lungs, even at low exp flow rates decr exercise abilityReduced lung elastic recoilLoss of radial contraction of airwaysIncr resistance of airways magnifies p drop across them decr intrabronchial p during expirationLow lungs vols

Work of Breathing Work = pressure x volume

People with stiff lungs take small rapid breaths, patients with severe airway destruction take slow breaths – these decr work done on lungs

Work measured by measuring O2 cost of breathing; efficiency thought to be 5-10%; O2 cost can be 5% in quiet breathing, up to 30% in forceful breathing

Efficiency % = useful work x 100 total E expended (or O2 cost)

Control Of Ventilation

Sensors:Central chemoreceptors: near ventral surface of medulla near exit of 9th and 10th CN’s; surrounded by brain ECF (composition determined by CSF, local blood flow, local metabolism) respond to changes in H+ conc of ECF (ie. CSF) and hence CO2, NOT O2CO2 effects pH of CSF: CSF separated from blood by BBB which is impermeable to H+ and

HCO3, but permeable to CO2; normal pH of CSF is 7.32, and as CSF has less protein it has poor buffering capability change in CSF pH for given conc CO2 is greater than in blood; if CSF pH is wrong for longer time, compensatory change in HCO3 due to transport across BBB which is prompter than renal compensation in blood therefore CSF pH has greater effect on ventilation than blood CO2

incr CO2 CO2 enters CSF liberates H+ ions activate chemoreceptors; incr CO2 cerebral vasodilation enhanced diffusion of CO2 into CSF

Peripheral chemoreceptors: carotid and aortic (in carotid and aortic bodies) chemoreceptors; carotid at bifurcation of carotid arteries, arotic bodies above and below aortic arch; contain 2 types of glomus cells; modulation of release of NT from cells change in discharge r of carotid body; have high blood flow

1) Type I cells – large dopamine content; close to ending of afferent carotid sinus nerve2) Type II cells – in carotid body

Respond to decr pO2, decr pH (only carotid), incr pCO2; nonlinear relation with pO2 – no change in firing until pO2 <100mmHg, then rate rapidly increases; respond to arterial rather than venous pO2; responsible for all changes in RR 2Y to hypoxaemia, pCO2 less important peripherally; fast response

Lung receptors:

Inspiration: intrapleural p ABCWork done = 0ABCD0Work done to overcome elastic forces = 0AECD0Work to overcome airway+tissue resistance = ABCEA; the more airway resistance, the more negative intrapleural p needs to becomeThe faster RR, faster flow rate, larger this area ABCEA is, but also 0AECD0

Expiration: intrapleural p CFAWork done = 0AECD0Work to overcome airway+tissue resistance = AECFA (this lies within

1) Pul stretch receptors : in airway SM; discharge 2Y to distension of lung impulses in vagus nerve slow RR via incr exp time (Hering-Breuer inflation reflex); similarily, deflation of lungs initiates insp activity (deflation reflex)

2) Irritant receptors : lie between airway epithelial cells impulses in vagus nerve bronchoconstriction and hyperpnoea; show rapid adaptation

3) J receptors : endings of nonmyelinated C fibres; in alveolar walls close to capillaries (supplied by pul circ); impulses in vagus nerve rapid, shallow breathing; may be stimulated in L heart failure and interstitial lung disease

4) Bronchial C fibres : supplied by bronchial circ; rapid shallow breathing, bronchoC, mucous secretion

5) Nose and upper airway receptors : respond to mechanical and chemical stimulation; sneeze, cough, bronchoC

Other receptors:1) Joint and muscle receptors : stimulus to ventilation in exercise, esp in early stages2) Gamma system : intercostal muscles and diaphragm sense elongation of muscle reflexly

controls strength of contraction; may be involved in sense of dyspnoea experienced on large resp efforts eg. in airway obstruction

3) Arterial baroreceptors : incr BP stimulation of aortic and carotid sinus baroreceptors hypoV and apnoea; vice versa

4) Pain and temp : heat hyperV; pain apnoea followed by hyperV

Central controller: Impulses from brainstem (pons and medulla contain respiratory centres)

1) Medulla: in reticular formation beneath floor of 4th ventriclea. Dorsal region of medulla: assoc with inspiration; have property of intrinsic periodic firing

for basic rhythm of ventilation: normal pattern is several secs of no activity AP’s increasing over next few secs insp muscle activity becomes stronger in ramp-like pattern finally cease and insp muscle tone return to preinsp level; this ramp is turned off by pneumotaxic centre inhibitory impulses inspiration shortened, so incr RR; also modulated by vagal and GP nerves

b. Ventral area assoc with expiration: only active in forceful breathing2) Apneustic centre in lower pons: excite insp area, prolonging ramp AP’s; may cause abnormal

breathing in brain injury3) Pneumotaxic centre in upper pons: inhibits inspiration as above; for fine tuning

Cortex can override for voluntary controlLimbic system and hypothalamus: can alter breathing in emotional states

Effectors: resp muscles; central controller keeps them working in coordinated manner

Integrated ResponsesResponse to CO2: pCO2 of arterial blood is most important factor, v sensitive; decr pCO2 decr stimulus to ventilation; most response 2Y to central chemoreceptors, but peri do contribute and are faster; response magnified if arterial pO2 low

Response to pCO2 decreased by sleep, increasing age, genetric, racial and personability factors; athletes and divers have low pCO2 sensitivity; morphine and barbs depress resp centre

Response to O2: response magnified if pCO2 high; role of pO2 in day-to-day alteration of ventilation small; hypoxic drive may become important in high altitude and severe lung disease (chronic CO2 retention pH of CSF normalizes, pH of blood normalized by renal compensation; arterial hypoxia is 1Y stimulus for ventilation; response 2Y to peripheral chemoreceptorsResponse to pH: this is independent of CO2; chief site of action is peri chemoreceptors, but large changes effect central chemoreceptors and resp centreResponse to exercise: during exercise there is normally slight decr pCO2, slight incr pO2, pH constant (may fall during severe exercise due to lactic acidosis); may be due to joint and muscle receptors in early stages; multiple theories

Abnormal BreathingCheyne-Stokes respiration: periodic breathing due to severe hypoxaemia; apnoea waxing then waning hyperventilation

Respiratory System Under Stress

ExerciseIncr GE demandsResting O2 consumption = 300ml/min 3000-6000ml/minResting CO2 output = 240ml/min 3000ml/minResting resp exchange ratio = 0.8 1.0 (or higher on severe exercise when anaerobic glycolysis)(reflects greater reliance on carbohydrate rather than fat for E)

Overall result: arterial pO2, pCO2 and pH little affected unless at v high work level

High AltitudeNormal barometric p = 760mmHg; exponential decr as move upwards, with concurrent decr pO2. Acclimatisation involves:

1) Hyperventilation: usually due to hypoxic stimulation of peri chemoreceptors low arterial pCO2 and alkalosis prevent hyperventilation by –ive feedback until CSF and blood pH normalizes then can hyperventilate again; sensitivity of carotid bodies to hypoxia increases during acclimitisation

2) Polycythaemia: incr O2-carrying capacity so even if arterial pO2 and sats decr normal O2 conc of arterial blood; slow to develop and of minor value

3) R shift of O2 dissociation curve better O2 unloading; due to incr 2,3-DPG due to resp alkalosis; at even higher altitudes there is L shift to aid with loadin of O2 in pul caps

4) Incr no caps beter unit vol in peri tissues5) Change in oxidative enzymes in cells6) Incr max breathing capacity as air is less dense

Also: pul vasoconstriction due to alveolar hypoxia incr pul art p incr work by R heart RVH and hypertension, may get pul oedema. Acute mountain sickness is due to hypoxaemia and alkalosis

O2 ToxicityCan cause changes in endothelial cells of pul caps, substernal distress, decr vital capacity; retrolental fibroplasias in newborn

O2 consumption incr linearly; above certain limit VO2 becomes constant (VO2max) – incr work above here needs anaerobic glycolysis Ventilation incr linearly at high VO2 values, due to lactic acid release, more incr ventilation due to ventilatory stimulus; change occurs at anaerobic threshold incr diffusing capacity of lung (incr diffusing capacity of membrane and vol of blood in pul capillaries due to recruitment and distension of capillaries due to incr CO and hence high pul art and venous p) incr CO linearly with work level due to incr HR and SV; change in CO is only ¼ that of change in ventilation decr ventilation-perfusion inequality due to more uniform distribution of blood flow O2 dissociation curve moves to R due to incr pCO2, H+ and temp easier O2 unloading decr PVR as caps open decr diffusion distance to tissues

Absorption atelectasis: if part of airway is trapped by mucus, total p in alveolus is high, but venous pO2 is still low (remember fall in pO2 from arterial to venous is greater than rise in pCO2 due to different shapes of dissociation curves) gas diffuses into blood collapse of alveoli; can occur when air is breathed, but process is slower – rate of collapse is prevented by absorption of N2 which is less soluble therefore moves less slowly out of alveoli; collapse most likely to occur at bottom of lung where parenchyma less well expanded

Space FlightNo gravity more uniform distribution of ventilation and blood flow improved GE incr thoracic blood vol as blood doesn’t pool in legs incr pul cap blood vol incr

diffusing capacity; postural hypotension on return to earth = cardiovascular deconditioning small decr haematocrit

Increased PressureDuring diving, p incr by 1 atmosphere per 10m descent; if lung, middle ear or intracranial sinus fails to communicate with outside p difference which may cause compression of descent, or overexpansion of ascent (must exhale on ascent to prevent overinflation of lungs)Incr density of gas at depth incr work of breathing

Decompression sickness: when diving, high pp of N2 (usually poorly soluble) forces it into solution in body tissues, esp fat (since N2 diffuses slowly, blood can’t carry N2, blood supply to adipose tissue is poor N2 between tissues and enviro takes hours) during ascent, N2 slowly removed from tissues; if ascent is rapid, bubbles of gaseous N2 form if large amount formed pain in joints, deafness, impaired vision, paralysis. Treatment is recompression forces bubbles back into solution then careful decompression; decr risk by using helium-O2 mixture (helium is ½ as soluble as N2 so less dissolves in tissues, low molecular weight so diffuses more rapidly through tissue, less dense so decr work of breathing); can’t use O2 as risk of O2 toxicity

Inert gas narcosis: at high pp N2 affects CNS euphoria, loss of coordination, coma; thought to be due to high fat:water solubility of N2

O2 toxicity: O2 stimulates CNS convulsions, nausea, ringing in ears, twitching of face (possibly due to inactivation of enzymes); so O2 conc must be decreased for deeper dives to avoid toxic effectsTraining incr caps and mitochondria in skeletal muscle

Hyperbaric O2 therapy: used in severe CO poisoning, to incr O2 dissolved in blood; anaemic crisis; gas gangrene

Polluted AtmospheresNO inflamm of URT and eye irritationSO, ozone bronchial inflammationOzone pul oedemaCO ties up HbHydrocarbons carcinogenicAerosols large particles removed by impaction in nose and pharynx swept away by mucus; medium-sized particles deposit in small airways (sedimentation) esp when flow velocity suddenly decreased – occurs in terminal and resp bronchioles; small particles deposit in alveolar walls by diffusion engulfed by macrophages

Liquid BreathingCan breathe liquid if high solubility of O2 and CO2; liquids have higher density so incr work of breathing; may develop CO2 retention and acidosis; can overcome opposite effect on O2 by incr inspired O2 conc

Perinatal Breathing

Placental GE: maternal blood enters intervillous sinusoids, fetal blood enters capillary loops that enter these spaces; GE across membrane 3.5μm distance; less efficient resulting in pO2 of fetal blood of 30mmHg;Placenta mixes with venous blood from fetal tissues IVC RA LA through PFO aing A brain and heartSVC RA RV pul art aorta via PDAOverall: best oxygenated blood reaches brain and heart (due to streaming in RA); lungs receive only 15% of CO

First breath: fetal lung is inflated with liquid (secreted by alveolar cells, with low pH) to 40% total lung capacity – as the larger the radius of curvature the smaller the pressure, this preinflation reduces pressure required; hypoxaemia and hypercapnia as placental GE interfered with, sudden incr sensitivity of chemoreceptors, external stimuli first breath (intrapleural p must fall to -40cm due to high viscosity of lung liquid compared to air) uneven expansion of lung, pulmonary surfactant stabilizes alveoli, lung liquid removed by lymphatics and capillaries

Circulatory changes: decr PVR due to abrupt incr alveolar pO2 decr hypoxic vasoC effects on pul art, incr vol of lung widens caliber of extra-alveolar vessels

incr pul blood flow incr LAp FO closes incr aortic p incr LAp decr RAp decr umbilical circulation incr LAp incr pO2 and locally circulating prostaglandins closes PDA

Tests of Pulmonary Function

VentilationForced expiration: FEV1 – vol exhaled in 1 sec (usually 80% of FVC); decreased by incr airway resistance or decr elastic recoil of lung, independent of exp effort (due to dynamic compression of airways – flow rate independent of resitance of airways downstream of collapse point, but determined by elastic recoil p of lung and resistance of airways upstream of collapse point, collapse point is in large airwaysFVC – total vol exhaledRestrictive disease (eg. pul fibrosis): FEV and FVC reduced; FVC reduced 2Y to decr compliance of lung or weakness of insp muscles; FEV1:FVC normal / increasedObstructive disease (eg. bronchial asthma): FEV1 reduced more than FVC; abnormal TLC, but exp ends prematurely (due to early airway closure due to incr SM tone, oedema of bronchial walls, secretions in airways); FEV1:FVC reducedFEF25-75%: av flow rate over middle half of expirationFRC: get pt to breathe 100 O2 for several mins to wash out all N2; conc of N2 in lung usually 80%; can slo use helium dilution technique which measures only ventilated lung vol; blody plethysmograph also includes gas trapped in airways

Diffusion: diffusing capacity of O2 v difficult to measureBlood flow: Fick principle and indicator dilution technique

Ventilation-Perfusion RelationshipsRegional differences: measured using radioactive xenon

Inequality of ventilation: Single breath method: N2 conc at lips measured following single breath of O2, N2 dilution of expired alveolar gas is is uniform giving nearly flat ‘alveolar plateau’; in lung disease alveolar N2 conc continues to rise on expiration due to uneven dilution and poorly ventilated alveoli which empty lastMultiple breath method: based on rate of washout of N2; if ventilation was uniform, N2 conc would decr by same fraction on each breath hence straight line; in diseased lung forms curved line as diff lung inuts have N2 diluted at diff rates

Inequality of Ventilation-Perfusion Ratio:Based on measurement of pO2 and pCO2 in arterial blood and expired gas; can work out mixed alveolar-arterial pO2 difference (can only really be used if blood flow wrong and ventilation OK) and ideal alveolar-arterial pO2 difference (using alveolar gas equation); in normal lung there is no ventilation:perfusion inequality and all units can represented by one ideal point on graph of pO2 vs pCO2; as inequality develops units spread awayDO FROM BOOK AND DRAW!!!

Blood Gases and pHNote: hypoventilation ALWAYS assoc with incr arterial pCO2; pO2 only fails to rise on administration of 100% O2 when shunt present; ventilation-perfusion inequality causes incr pCO2 in absence of incr ventilation

Mechanics of BreathingLung compliance: vol change per unit pressure change across lung; oesophageal p is measured and assumed to be close to intrapleural p; get pt to breath out from TLC measuring oesophageal p p-vol curve; compliance = the slope of this curve; can also be measured during resting breathing by measuring intrapleral p at end-insp or end-exp which reflects elastic recoil forces unassociated with airflow (this doesn’t work in lung disease as airflow in lung persists even when air at lips has stopped due to diff dynamics; indeed sometimes air still entering part of lung when exp elsewhere begins air enters that part of lung (pendelluft) as incr RR, less tidal vol enters partially obstructed area decr lung compliance)Airway resistance: p difference between alveoli and mouth per unit airflow; measured using blod plethysmograph

USE DIAGRAMS FROM HERE

Flow-volume curve: remember after small amount gas exhaled, flow limited by airway compression and determined by elastic recoil force of lung and resistance of airways upstream of collapse pointRestrictive: max flow rate decreased, total vol exhaled decreased; flow rate unnaturally high during latter part of expiration due to incr lung recoilObstructive: max flow rate decreased, total vol exhaled decreased; low flow rate in relation to lung vol throughout

RENAL PHYSIOLOGY

Renal Anatomy

The Nephron: human kidney contains 1.3 million nephrons; cortical nephrons have short LOH, juxtamedullar nephrons (15%) have long LOH extending into medullary pyramids; 45-65mm long1) Renal tubule: total SA 12m2

a) PCT: 15mm long, 55μm diameter; cells connected by tight junctions; between bases of cells are lateral intercellular spaces; luminal edges of cells have brush borderb) ding LOH: thin, permeable cellsc) thick aing LOH: thick cells containing many mitochondrial; reaches back up towards glomerulus and nestles between eff and afferent arterioles macula densa of specialized cells found here (lacis cells an renin-secreting juxtaglomerular cells form JGA)d) DCT: starts at MD; 5mm long; no BBe) CD: 20mm long; enter into renal pelvis at pyramids; contains principal (P) cells (tall with few organelles; for Na reabsorption and ADH-stimulated H20 reabsorption) and intercalated (I) cells (less, have microvilli, cytoplasmic vesicles and mitochondria, for acid secretion and HCO3 transport); some cells secrete PGE2

2) Glomerulus: 200μm diameter; formed by invagination of capillaries into Bowman’s capsule; capillaries supplied by afferent arterioles, drain into efferent arterioles; permits passage of neutral substances up to 4nm diameter

Only 2 layers – endothelium of capillaries: fenestrated with pores 70-90nm diameter; total area 0.8m2

capsule epithelium: made up of podocytes which interdigitate to form filtration slits (25nm wide and closed by thin membrane) along capillary wall

separated by basal lamina with mesangial cells between lamina and endothelium (contractile and control filtration, secrete substances, take up immune complexes)

Blood vessels: 1.2-1.3L blood/min (approx 25% of CO); Vol of blood in renal caps at any time is 30-40mLAfferent arterioles (short, straight branches of interlobular arteries) multiple capillaries in glomerulus (capillary pressure usually approx 45mmHg; 40% SAP)) coalesce to efferent arteriole (contains little SM)

peritubular capillaries in network to supply tubules in multiple nephrons (pressure usually approx 8mmHg)

or if from juxtamedullary glomeruli vasa recta hairpin loops along LOH; ding have nonfenestrated epirhtleium containing transporter for urea, aing have fenestrated epithelium to conserve solute

interlobular veins renal vein (pressure usually approx 4mmHg)Cortical blood flow: mostly for filtration through glomerulus; great (5ml/g/min) with little O2 extracted (pO2 50mmHg); Medullary blood flow: low (0.6-2.5ml/g/min); large amounts of O2 extracted (pO2 15mmHg); sensitive to hypoxia if flow decreased

Priniciples of Renal Function

Renal plasma flow = amount of substance exreted per unit time / renal AV difference (applying Fick’s principle); can be measured using p-aminohippuric acid (has high extraction ratio; PAH is filtered and secreted); ave 625ml/min

Effective renal plasma flow (doesn’t use venous conc)= Urine conc X urine flow = clearance of PAH Plasma conc

Actual renal plasma flow = effective / extraction ratioExtraction ratio = arterial conc – venous conc

arterial conc

Renal blood flow = renal plasma flow x (1 / 1 – Hct) (1.2-1.3L blood/min)

Regulation of renal blood flow: NE constricts renal vells, mostly interlobular arteries and afferent arteriolesDopamine made in kidney vasodilation and natiuresisAngiotensin II efferent vasoCPG incr blood flow in renal cortex, decr blood flow in renal medullaAch renal vasoDAutoregulation: probable direct contractile response of SM to stretch; NO may be involved; NO, PG, cardiovascular peptides involved in maintaining balance of medullary/cortical blood flow; renal blood flow maintained if efferent constriction > afferent

Nerve supply: Sympathetic preganglionic innervation from lower thoracic and upper lumbar segments; cell bodies of postganglionic neurons in sym ganglion chain, in sup mesenteric ganglion and along renal artery; PCT, DCT and aing LOH richly innervated

Stimulation incr renin secretion (via NE effect on β1-adrenoceptors on juxtaglomerular cells) incr Na reabsorption (via NE effect on renal tubular cells) renal vasoC decr filtration, decr renal blood flow (mostly via α-adrenoceptors)

Pain travels with sym efferents

Glomerular filtration: normal = 125ml/min (7.5L/hr, 180L/day) 1L/day urine, so 99% reabsorbed; values for women are 10% lower; amount filtered is product of GFR and plasma level of substanceMeasured by measuring excretion and plasma level of substance freely filtered at glomerulus and neither secreted/reabsorbed by tubules; must be non-toxic and not metabolized by bodyeg. inulin (note creatinine is NOT accurate as some is secreted and reabsorbed)Amount in urine must be provided by filtering the exact amount of plasma that contained this amount so:

GFR = (urine conc of Y) x (urine flow per unit time) = clearance of Y arterial plasma level of Y

Factors governing filtration: Size of capillary bed - contraction of mesangial cells decreases this; angiotensin II importantPermeability of capillaries – 50x that of capillaries in skeletal muscle; cannot pass through if >8nm size; decr for anionic substances, incr for cationic substances; albumin is negatively charged (anion), albuminuria due to nephritis due to loss of negative charges in glomerular wall which usually decreases filtration of albuminHydrostatic and osmotic p gradients across capillary wall – high p in glomerular capillaries as efferent vessels have high resistance; osmotic p gradient is usually negligible; net filtration p is 15mmg at afferent end drops to 0 at efferent end as equilibrium reached (uncertain whether this is reached in humans); exchange across capillaries is flow-limited rather than diffusion limited, some portions of capillaries don’t participate

Kf = glomerular ultrafiltration coefficient (product of glomerular capillary wall permeability and filtration surface area)Pgc = mean hydrostatic p in glomerular capillariesPt = mean hydrostatic p in tubuleOgc = osmotic pressure of plasma in glomerular capillariesOt = osmotic pressure of plasma in tubule

GFR = Kf [(Pgc - Pt) – (Ogc – Ot)]

Filtration fraction: ratio of GFR to renal plasma flow; normally 0.16-0.2; when decr systemic BP GFR falls less than RPF incr filtration fraction

Tubular Function:

Amount excreted per unit time = amount filtered + net amount transferred by tubulesClearance = GFR if no net tubular secretion/reabsorption

> GFR if net secretion < GFR if net reabsorption

Reabsorption/secretion may occur by:EndocytosisParacellular diffusion: through tight junctionsPassive diffusion, facilitated diffusion, ion channels, exchangers, cotransporters, pumps

AT systems have a transport maximum (max rate) at which they can transport solute – at higher concs becomes saturated

Lymphatics: abundant supply thoracic ductRenal capsule: thin but tough; limits swelling incr renal interstitial pressure decr glomerular filtration

Arterioles and glomeruli secrete PGI2 (prostacyclin)In interstitium in medulla are type I medullary interstitial cells – secrete PGE2

Reabsorption in Specific Areas

PCT: AT of solutes (60-70%)H20 passively out (60-70%) along osmotic gradient via aquaporin-1 isotonicity maintainedNa reabsorption (60%): Na-H exchange in PCT AT into interstitial space or lateral intercellular

spaces via Na-K ATPase (3Na, 2K)Glu reabsorption: mostly reabsorbed in PCT; glu and Na bind carrier SGLT2 in luminal

membrane (Na moves down gradient taking glu with it) Na pumped into interstitium, glu via GLUT2 (usually binds d isomer)

aa reabsorption: Cotransport with Na in luminal membrane Na pumped out by Na-K ATPase, aa via passive/facilitated diffusion

NB. Glu reabsorption: amount reabsorbed proportionate to (plasma glu level x GFR) up to transport maximum; filtered at approx 100mg/min; Renal threshold is level at which glu first appears in urine = 180mg/dl venous level (this is lower than expected as reabsorption splays from ideal curve as renal threshold not same in all tubules)

LOH: fluid in ding LOH becomes hypertonic as H20 passes out becomes more dilute as moves up aing LOH as H20 trapped hypotonic to plasma at top; Bartter’s syndrome due to

defective transport in aing LOH Na loss hypovolaemia stimulation of RAA hypertension, hyperkalaemia, alkalosisH20 reabsorption: 15% filtered water reabsorbed; ding limb permeable to H20; aing limb

impermeable to H20Na reabsorption (30%): Na-2Cl-K cotransporter in thick aing LOH AT into interstitium by Na-

K ATPaseK reabsoprtion: Na-2Cl-K cotransporter in thick aing LOH K diffuses back into tubular lumen

or back into interstitium via ROMKCl reabsorption: Na-2Cl-K cotransporter in thick aing LOH Cl enters interstitium via CIC-Kb

channelsDiuretics: loop (eg. frusemide, ethacrynic acid, bumetanide) inhibit Na-K-2Cl cotransporter

natiuresis and kaliuresis

DCT: relatively impermeable to H20; continued removal of solutes further dilutes urineH20 reabsorption: 5% filtered water reabsorbedNa (7%) and Cl reabsorption: Na-Cl cotransporter in DCTDiuretics: metolazone, thiazides (eg. chlorothiazide) inhibit Na-Cl cotransporter

CD’s: Na reabsorption (3%): ENaC channels in CD (regulated by aldosterone)H20 reabsorption (10% in cortex, 4.7% in medulla): depends on vasopressin (ADH from PPG

which acts on V2 receptor cAMP and PKA incr permeability to H20 due to insertion of aquaporin-2 into apical membranes of cells from vesicles stored in cytoplasm of principal cells) H20 moves out of hypotonic CD cortical interstitiumWhen ADH absent, CD relatively impermeable to H20 so urine stays hypotonic – but 2% H20 can be reabsorbed in absence of ADH

Diuretics: H20 inhibits ADH secretion ETOH inhibits ADH secretion V2 antagonists inhibits action of ADH on CD K-sparing (eg. spironolactone, triamterene, amiloride) inhibit Na-K exchange but inhibiting aldosterone (spironolactone) or ENaCs (amiloride)

Conc mechanism dependent of maintenance of gradient of incr osmolality along medullary pyramids maintained by countercurrent mechanism of LOH and vasa recta (dependent on AT of Na and Cl out of aing limb and high permeability of ding limb to H20, inflow through PCT and outflow through DCT) – see pics; this is greater in longer (JM) nephrons; osmotic gradient and hypertonicity of interstitium maintained by vasa recta countercurrent mechanism (solutes move out of vessels going towards cortex and into vessel descending into pyramid, H20 into descending vessels and out of ascending vessels solutes recirculate in medulla but H20 bypasses it; removes H20 from CD’sUrea contributes to osmotic gradient in medullary pyramids; urea transporters are facilitated diffusion (UT-A1 – 4)Magnitude of osmotic gradient increased when decr r of flow in LOH urine becomes more concentrated

H20 excretion: 180L filtered/day, at least 87% is reabsorbed; absorption of H20 can be altered without changing solute excretion; aquaporins 1,2,5,9 have been found in humans (9 in WBC, liver, lung spleen; 5 in lacrimal glandsH20 diuresis: normal reabsorption of H20; begins 15mins, peaks 40mins post ingestion; max urine flow is 16ml/minH20 intoxication: swelling of cells when max urine flow reachedOsmotic diuresis: decr reabsorption of H20; due to unreabsorbed solutes (eg. mannitol; glu when capacity exceeded) in tubules; note that conc grad against which Na can be pumped out of PCT is limited, usually maintained by H20 reabsorption in PCT but this is decreased if there are unreabsorbable solutes in PCT decr reabsorption of H20 and Na in LOH (mainly due to decr action of Na-K-2Cl cotransporter in aing LOH ) and CD due to decr medullary hypertonicity Free water clearance: CH20 is negative when urine is hypertonic, +ive when hypotonic

CH20 = urine flow rate - (urine osmolality) x (urine flow rate) (plasma osmolality)

Tubuloglomerular feedback: as rate of flow increases through aing LOH and DCT, filtration decreases so constant load delivered to distal tubule; sensor is macula densa (amount of fluid is related to amount of Na and Cl Na and Cl enter macula densa cells via Na-K-2Cl cotransporter in apical membranes incr Na causes incr Na-K ATPase activity incr ATP hydrolysis incr adenosine formed works via A1 receptors on macula densa cells to incr release of Ca to vascular SM in afferent arterioles afferent vasoC decr GFRGlomerulotubular balance: incr GFR causes incr reabsorption of solutes and water in PCT; occurs within seconds; thought to be due to oncotic p of capillaries

Other diuretics: xanthines (eg. theophylline, caffeine) decr tubular reabsorption of Na, incr GFR acidifying salts (eg. CaCl2, NH4Cl) supply H H buffered and Na is replaced with H

an anion is excreted with Na when this ability is exceeded CA inhibitors (eg. acetazolamide) decr H secretion incr Na and K excretion, depressed

HCO3 reabsorption NB. Both thiazide and loops cause incr delivery of Na to Na-K exchange area if CD

incr K excretionH Secretion in PCT, DCT, CD

PCT: H comes from intracellular dissociation of H2CO3 (formation of this cataylsed by carbonic anhydrase – drugs that inhibit this enzyme decr secretion of acid in PCT)

1 H secreted via Na-H exchanger (1H out, 1Na in - gradient for Na maintained by Na-K ATPase)1 HCO3 reabsorbed via diffusion into interstitial fluid

Buffer: H reacts with HCO3 H2CO3 CO2 and H20; CA in brush border facilitates this CO2 re-enters tubular cells to form more H2CO3For each mol HCO3 removed from urine in this reaction, 1mol HCO3 enters blood and hence is reabsorbedMost H has no effect on pH of urine due to formation of CO2 and H20

DCT H secretion independent of Naand CD: ATP-driven H pump in intercalated cells (in acidosis, action increased by deposition of

more of these pumps in membranes); increased activity by aldosteroneAlso a H-K ATPaseCl-HCO3 exchanger transports HCO3 into interstitial fluid

Buffer (PCT and DCT): NH3 is lipid soluble and diffuses down conc gradient into interstitial fluid and urine via nonionic diffusion reacts with H NH4 which remains in urinePriniciple reaction producing NH4 in cells is glutamine glutamate + NH4 (enzymeglutaminase); glutamate may α-ketoglutarate + NH4 (enzyme glutamic dehydrogenase); αketoglutarate metabolized using 2H and freeing 2HCO3Incr secretion of NH3 and excretion via NH4 in chronic acidosis (adaptation)

Buffer (DCT and CD): H reacts with HPO4 H2PO4 as PO4 is highly concentrated here due to reabsorption of H20DCT has less ability to secrete H than PCT, but secretion has more effect on pH

Limiting pH of urine is 4.5 (can go from 4.5 – 8.0) – below this secretion stops (ie. in CD’s); buffers important; H cause urinary titratable acidity (amount of alkali that must be added to urine to return pH to 7.4 – this doesn’t account for H2CO3 which has been converted to H20 and CO2)Secretion limited by changes in:

Intracellular pCO2 (incr pCO2 incr H2CO3 available to buffer, H secretion enhanced)K (decr K enhanced H secretion)CA (CA inhibition decr H secretion as less formation of H2CO3)Aldosterone (incr aldosterone incr transport of Na incr secretion of H and K)

HCO3 ExcretionHCO3 reabsorption is proportionate to amount filtered over wide rangeWhen high plasma HCO3 HCO3 appears in urine, urine becomes alkalineWhen low plasma HCO3 secreted H no longer used to reabsorb HCO3 H must combine with buffers acidic urine, with higher NH4 content

Na ExcretionNormally 96-99% filtered Na is reabsorbed; urinary Na output can change a lot depending of diet. Determined by:

1) GFR: affected by tubuloglomerular feedback etc…2) Reabsorption: governed by

a. Aldosterone (adrenal mineralocorticoid): incr reabsorption Na acting primarily on CD’s by incr number of active ENaC’s; also incr Cl reabsorption and incr K and H secretion; eventually kidneys escape effect of steroid (escape phenomenon) preventing oedema, this phenomenon is absent in nephrosis, cirrhosis, heart failure

b. PGE2: inhibits Na-K ATPase and ENaCs excretion of Nac. Endothelin and IL-1 incr formation of PGE2 excretion of Na

d. Ouabain inhibits Na-K ATPase excretion of Nae. Angiotensin II action of PCT incr reabsorption of Na and HCO3

K ExcretionMuch is reabsorbed in PCT THEN secreted by DCT and CD (much of K movement is passive, so rate of secretion proportionate to rate of flow); amount secreted equal to K intake; secretion of K in CD related to reabsorption of Na (which is related to excretion of H), so decr K excretion when decr Na reaching distal tubule or when incr H secretion

Renal Disease proteinuria – usually albuminaemia hypoproteinaemia decr oncotic p, decr plasma vol, oedema loss of conc and diluting ability polyuria/nocturia; in advanced renal disease loss of countercurrent mechanism and loss of functioning nephrons nephrons compensate by producing osmotic diuresis damages nephron oliguria and anuria uraemia anaemia 2Y hyperparathyroidism (due to 1,25-dihydroxycholecalciferol) acidosis – urine is maximally acidified and decr renal tubular production of NH4 so decr H secretion abnormal Na metabolism – Na retention due to decr filtration (GN) / incr aldosterone (nephrotic syndrome, due to decr plasma proteins decr plasma vol due to interstitial oedema trigger RAA) / heart failure

The Bladder

Filling: walls of ureters contain SM in spiral, longitudinal and circular bundles; regular peristalsis; oblique passage through bladder wall prevents refluxEmptying: also spiral, longitudinal and circular (detrusor) muscle; internal urethral sphincter doesn’t encircle; external urethral sphincter is skeletal muscle; intravesical p not raised until bladder well filled (as radius increases; law of Laplace – pressure = 2x wall tension / radius); plasticity – when bladder stretched, tension initially produced not maintained; sharp rise in p as micturition reflex produced – first urge to void felt at 150ml, marked sense of fullness at 400mlMicturition: contraction of detrusor emptying; micturition is sacral spinal reflex (initiated by stretch receptors in bladder wall) initiated at 300-400ml facilitated and inhibited by higher brain centres which alter threshold for voiding reflex; afferent limb of reflex travels in pelvic nerves, paraS efferent limb also travel in pelvic nerves

Facilitatory area – in pontine regionInhibitory area – in midbrainTransection above pons threshold for voiding loweredTransection at top of midbrain reflex normalEffect of deafferentation – all reflex contractions stop; bladder becomes distended and hypotonic; some contraction maintained due to intrinsic response of SM to stretchEffect of deafferent- and deefferentation – flaccid and distended, but later becomes shrunken with hypertrophied wall and many contractions due to denervation hypersensitisationEffect of SC transaction – during spinal shock flaccid and unresponsive overfilled with overflow incontinence voiding reflex returns but without voluntary control; voiding reflex may become hyperactive

Regulation of ECF Volume and Composition

Tonicity Plasma osmolality 280-295mosm/kgTotal blood osmolality α total body Na + total body K / total body H20 changes occur when disproportion between amount of electrolytes and amound of H20Incr osmolalilty release of vasopressin and stimulation of thirst

Volume

Determined by amount of osmotically active solute in ECF; Na most important factorDecr vol incr aldosterone, vasopressin, AII (also causes thirst and constricts BV’s); incr vol incr ANP and BNP from heart natiuresis and diuresis; volume overrides osmotic regulation

Buffers (Henderson-Hasselbach Equation) NB. ANION (-)If acid is added: eq shifts to L levels of ‘buffer anions’ (A-) drop as they react with added H less effect on pH

Anions of added acid excreted by renal tubules with a ‘covering’ cation (usually Na) to maintain electrochemical neutrality

2NaHCO3 + H2SO4 Na2SO4 + 2H2CO3Kidney then replaces Na with by H, so reabsorbing Na and HCO3 (effectively reversing the above)

Na2SO4 + 2H2CO3 2NaHCO3 + 2H+ + SO42-H+ and SO4 excreted

If base added: eq shifts to R; H ions bind OH, but more H ions released so less effect on pHBuffering capacity greatest when amount of free anion = amount of undissociated acid (when A/HA = 1 log[A][HA] = 0 pH = pK); K applies to infinitely diluate solutions in which interionic forces are negligible

HA H+ + A- [H+] x [A-] = K pH = pK + log [A-] HA [HA]

Regulation of H ConcNote a decr in pH by 1 unit is a 10-fold incr in H conc; pH of blood is pH of true plasma that has been in equilibrium with RBC (as RBC contain Hb which is an important buffer); normal arterial pH is 7.4 (venous slightly lower; acidosis <7.4, alkalosis >7.4)

H load comes from:Aa metabolism: H load of 50meq/day

Aa in liver for gluconeogenesis NH4 + HCO3 NH4 incorporated into urea and protons produced bufferered by HCO3, so little NH4/HCO3 enter circulation

Metabolism of other aa H2SO4, H3PO4 (strong acids) major H loadCO2 metabolism: usually hydrated to H2CO3 and excreted by lungs/kidneys; H load of 12,500meq/dayExercise lactic acidDiabetic ketosis acetoacetic acid and β-hydroxybutyric acidRenal failure

Buffers in blood:Plasma proteins: free carboxyl and amino groups dissociate

HProt Prot- + H+

eg. RCOOH RCOO- + H+ pH = pK(RCOOH) + log [RCOO-] [RCOOH]

eg. RNH3+ RNH2 + H+ pH = pK(RNH3+) + log [RNH2] [RNH3+]

Haemoglobin: dissociation of imidazole groups of histadine residues; also has free carboxyl and amino groups; present in large amounts so 6x buffering capacity of p proteins

HHb H+ + Hb –

Carbonic acid – bicarbonate system: first system is difficult to measure as low H2CO3 and low pH; however H2CO3 is in equilibrium with CO2 2nd system (in clinical practice, [CO2] is x by 0.301 as this

is solubility coefficient) – this system still has low pK, but is most effective buffer system as amount of dissolved CO2 can be controlled by respiration and HCO3 can be controlled by kidneysWhen H added: H2CO3 formed, HCO3 declines; extra H2CO3 converted to CO2 (excreted by lungs effectively as incr H causes incr RR) and H2O so H2CO3 conc doesn’t rise and pH isn’t altered muchNB. CA inhibited by cyanide, azide, sulfide, sulfonamides

1) H2CO3 H+ + HCO3- pH = pK (3) + log [HCO3] [H2CO3]

2) H2CO3 CO2 + H20 (CA catalyst) pH = pK (6.1) + log [HCO3-] [CO2]

Buffers in interstitial fluid: carbonic acid – bicarbonate system as abovBuffers in intracellular fluid: proteins as shown aboveAlso H2PO4 H+ + HPO42-Buffers in CSF and urine: bicarbonate and phosphate systems

Acidotic/Alkalotic StatesResp acidosis: retained CO2 is in equilibrium with H2CO3, which is in equilibrium with HCO3- incr HCO3-; most buffering is intracellular; renal compensationResp alkalosis: decr pCO2; most buffering is intracellular; renal compensationMetabolic acidosis: when acids stronger than buffers are added to blood; only 15-20% acid load will be buffered in ECF, the rest dealt with intracellularily; incr H incr RR (resp compensation), renal compensation causes excretion of HMetabolic alkalosis: when alkali added to blood; incr plasma HCO3 and pH; 30-35% OH load buffered intracellularily; resp compensation with decr RR; renal compensation as below

Renal compensation: HCO3 reabsorption depends on filtered load of HCO3 (affected by GFR and plasma HCO3 level)

rate of H secretion by renal tubular cells (as HCO3 is reabsorbed in exchange for H) which is α pCO2

In resp acidosis incr renal tubular H secretion, incr HCO3 reabsorption incr plasma HCO3 incr pHIn resp alkalosis decr renal H secretion, decr HCO3 reabsorption decr plasma HCO3 decr pHIn metabolic acidosis anions(-) are filtered (each with a cation, Na) in renal tubules tubules then secrete H in exchange for 1Na and 1HCO3 urinary buffers then tie up H so this can continue; when acid load v large, cations are lost with anions diuresis; glutamine synthesis by kidneys increased incr supply of NH4 to kidney, can also be converted to α-ketoglutarate which produces HCO3 to help bufferIn metabolic alkalosis

ABG’sCan measured pCO2 and pH then calculate HCO3Venous gas: has pCO2 7-8mmHg higher, pH 0.03-0.04 unit lower, HCO3 2mmol/L lowerAnion gap: difference between conc of cations (+) other than Na and conc of anions (-) other than Cl and HCO3 in plasma. Consists mainly of proteins in anionic form and organic acids

Increased (eg. ketoacidosis, lactic acidosis) decr plasma conc of K, Ca, Mg incr conc/charge of/on plasma proteins incr organic anions in blood (eg. lactate, aspirin)

Decreased: incr cations (+) decr plasma albumin

Normal (eg. hyperchloraemic acidosis – eg. due to CA inhibitors)

DO LAST BIT WITH SIGGAARD-ANDERSON CURVE NOMOGRAM

METABOLISM

Metabolism: chemical and E transformations occurring in body produce CO2 and H20Catabolism: oxidation liberating small amounts of EAnabolism: formation of substances taking UP energy

Energy Metabolism

Metabolic Rate: Amount of E liberated per unit timeAmount of energy liberated by catabolism of food in body = amount liberated when food burned outside of body

Energy output = external work + E storage (0 or –ive if fasting) + heatEfficiency = work done / total E expended (eg. 50% for isotonic muscle contractions)

Factors:1) Muscular exertion: O2 consumption incr for long time afterwards 2Y to O2 debt2) Recently ingested food: assimilation of food into body produces specific dynamic action (SDA)3) Environmental temp: U-shaped; when lower than body, shivering etc…; when higher metabolic

processes elevate 14% for every degree elevation; MR @ rest in comfy temp 12-14hrs after last meal = BMR (decr by 10% during sleep, by 40% with prolonged starvation) = 2000kcal/day in normal man

4) Others: height, weight (BMR = 3.52W0.75), sex, age, growth, reproduction, lactation, emotional state, thyroid hormones, E and NE

Calories (gram/small/standard): Amount of heat E needed to raise temp of 1g H20 by 1 degree1kcal = 1000calCalorimetry – burn foodstuffs outside body and measure heat producedIndirect calorimetry – measure O2 consumption per unit time (as O2 isn’t stored) which is α metabolismCarbohydrate = 4.1 kcal/g Fat = 9.3 kcal/g Protein = 5.3 kcal/g (in body, incomplete so 4.1)

Respiratory Quotient (RQ): SS vol of C02 produced : vol O2 consumed per unit timeWork out O2 consumed = blood flow per unit time x AV difference between O2 concsRespiratory Exchange Ratio (R): CO2 : O2 at any given time whether or not equilibrium reachedRQ carbohydrate = 1 (as H and O present in same amount as H20) (RQ brain 0.97-0.99 so primary E source is carbohydrate)RQ fat = 0.7 (as extra O2 needed for formation of H20)RQ protein = 0.82During exercise: incr R as lactic acid converted to C02 during anaerobic glycolysisMetabolic acidosis: incr R as incr CO2 being expiredMetabolic alkalosis: decr R

Intermediary Metabolism

E stored in high/low-energy phosphate compounds which have bonds between phosphoric acid residues and organic compounds released when bond hydrolysed

Eg. ATP ( ADP releasing E, AMP releasing E) – formed by oxidative phosphorylation which takes up 80% basal E consumption; 27% used for protein synthesis, 24% Na-K ATPase, 9% gluconeogenesis, 6% Ca ATPase, 5% myosin ATPase, 3% ureagenesisEg. Creatine phosphate (phosphorylcreatine, CrP) – found in muscleEg. Thioesters (eg. Coenzyme A)

Digestion aa, fat derivatives, fructose, galactose, glucose absorbed metabolized to short-chain fragments (common metabolic pool, intermediates ie. High/low E phosphate compounds)

carbohydrates, proteins and fats made enter citric acid cycle hydrolysis E and H and CO2 H20

Oxidation: combination of a substance with O2 / loss of H / loss of electronsCatalysed by co-enzymes (organic, non-protein) and co-factors (simple ions) which act as carriers for products of reaction (eg. Accept H)

Eg. Nicotinamide adenine dinucleotide (NAD) NADHEg. Dihydronicotinamide adenine dinucleotide (NADP) NADPHEg. Flavin adenine dinucleotide (FAD) FADH)

H from NADH and NADPH then transferred to…Flavo-protein- cytochrome system (in mitochondria) – a chain of enzymes which are reduced then reoxidised final enzyme cytochrome c oxidase which transfers H to O2 H20

Reduction: reverse of above

Carbohydrate Metabolism

Made up of glucose, galactose and fructose; principle product of carbohydrate digestion is glucoseFasting plasma glu = 70-110 mg/dL (3.9-6.1mmol/L); 15-30mg/dL higher in arterial bloodNormal 70kg man has 2500kcal stored in 400g muscle glycogen, 100g liver glycogen, 20g glu; 112,00kcal stored in fat (80%)Glu load: 50% CO2 and H20

5% glycogen 30-40% fat

Factors affecting glu level:1) Dietary intake2) Rate of entry of glu into cells3) Glucostatic activity of liver – 5% converted into glycogen, 30-40% converted into fat

Renal handling of glucose: renal threshold is 180mg/dL glycosuria

Exercise: during exercise plasma glu raised by hepatic glycogenolysis; muscles use glycogenolysis with incr uptake glu; incr gluconeogenesis; decr insulin; incr glucagon and E@ rest: brain uses 70-80% glu, rest by RBC; muscles use fa’s for metabolism

1) Glucose enters cells phosphorylated to glucose 6-phosphate Catalysed by hexokinase; in liver catalysed by glucokinase which has greater affinity for glu and incr by insulin, decr by diabetes/starvation1 mol ATP used for conversion of glu to G6P

2) G6P polymerized to glycogen (glycogenesis; G6P G1P uridine diphosphoglucose (UDPG) glycogen catalysed by glycogen synthase (dephosphorylated form active, phosphorylated form inactive); a protein primer named glycogenin is required, and its availability limits reaction) stored in liver and skeletal muscle

or catabolised (glycolysis) pyruvate and lactate via 2 pathways

1) Embden-Meyerhof pathway: via cleavage through fructose to triosea. 1 mol ATP used for converstion of fructose 6-phosphate to fructose 1,6-diphosphate

2) Direct oxidative pathway (hexose monophosphate shunt): oxidation and decarboxylation to pentoses

3) phosphoglyceraldehyde phosphoglycerate (this reaction ANAEROBICALLY releases 1 mol ATP; requires NAD+ and produces NADH)

4) phosphoglycerate phosphoenolpyruvate

5) phosphoenolpyruvate pyruvate (this reaction ANAEROBICALLY releases 1 mol ATP) NB. Via EM pathway, 2 phosphoglyceraldehyde produced, so 4 ATP produced ANAEROBICALLY per mol glu, but 1 mol ATP used net production of 3 ATP per mol G6P (this figure is 2 ATP if made from glu))

6) pyruvate lactate (in this reaction pyruvate accepts H from NADH (when needed under anaerobic

conditions) produced in 3) thereby reforming NAD+ needed for above reaction; lactate produced converted back to pyruvate when O2 restored as H then accepted by flavoprotein-cytochrome chain)

proteins (gluconeogenesis – regulated by PGC-1, a transcriptional coactivator, induced by fasting)

acetyl-CoA (this is IRREVERSIBLE; this reaction requires NAD+ and produces NADH)

7) Acetyl-CoA enters citric acid/Krebs/tricarboxylic acid cycle with oxidation of carbohydrate/fat/protein to CO2 and H20; AEROBIC)

joins oxaloacetate forms citrate 7 subsequent reactions release 2 CO2 4 H transferred to flavoprotein-cytochrome chain (2 from NADH from step 3, 2 from

NADH from step 6) overall producing 12 ATP and 4 H20 (2 H20 used in cycle)

24 ATP formed by subsequenct 2 turns of cycle

So, net production by EM pathway and CA cycle = 38 ATPIf hexose monophosphate shunt used, amount ATP released depends on amount of NADPH convered to NADH then oxidized.

Aa’s intermediates in reactions; hence non-glucose protein molecules converted to gluNB. Glu makes fat through acetyl-CoA but since this is a one-way reaction there is very little conversion of fat to carbohydrate, but there can be conversion of glycerol (from fat) dihydroxyacetone phosphate (muscle uses fa’s for metabolism)

Directional flow valves: when enzymes can make reactions unidirectional hence effect metabolism

Glycogenolysis: catalysed by phosphorylase which is activated by: 1) E working on beta-2 receptors in liver (incr cAMP activation of PKA phosphorylase kinase

activated phosphorylates phosphorylase activating it – phosphorylated form active (a), dephosphorylated inactive (b))

2) E working on alpha-1 receptors in liver intracellular Ca activation of phosphoylase kinase independent of cAMP

Glycogen G6P glucose (via glucose-6-phosphatase which is present in liver; other tissues don’t have this enzyme to G6P follows route above incr lactate)Glucagon: only stimulates phosphorylase in liver so will cause incr plasma gluE: stimulates phosphorylase in liver and skeletal muscle, so will cause incr plasma glu and lactateMcArdle’s syndrome: deficiency of muscle phosphorylase

Other hexoses: 1) Galactose phosphorylated reacts with UDPG to form uridine diphosphogalactose (can be

used for formation of glycolipids and mucoproteins) converted to UDPG glycogen synthesis; utilization of galactose requires insulin

2) Fructose F6P (catalysed by hexokinase or fructokinase) F1,6P split into dihydroxyacetone phosphate (which enters pathway for glu metabolism) and glyceraldehydes (which is phosphorylated); these reactions are independent of insulin; F6P can also form F2,6DP (regulates gluconeogenesis; high F2,6DP level incr breakdown of F6P to F1,6P so incr pyruvate; low F2,6DP level incr gluconeogenesis; glucagons decr F2,6DP)

Protein Metabolism 2-10 aa = peptides; 10-100 aa = polypeptides; >100 aa = proteins1g/kg body weight / day desirable for needsSupplies 9.3 kcal/g

Essential aa = must be obtained from diet; Aa pool = supplies needs of body; hormones made from aa’s

Protein Formation:Proteins made of aa’s linked by peptide bonds joining amino to carboxyl group; aa’s are acidic/neutral/basic in reaction; Glycoproteins contain carbs, lipoproteins contain lipids; Body’s own proteins being constantly broken down and reformed; turnover rate 80-100g/day; during growth synthesis > breakdownOrder of aa in peptide chain = 1Y structure; twisting and folding = 2Y structure (eg. α-helix; β-sheet); arrangement of twisted chains into layers, crystals or fibres = 3Y structure; arrangement of subunits = 4Y structure

Use of protein:1) Formation of hormones (eg. Thyroid, catecholamines, histamine, serotonin, melatonin2) Formation of urinary sulfates: via oxidation of cysteine; SO4 will be excreted accompanied by

Na/K/NH4/H; ethereal sulfates are fromed in liver from oestrogens, steroids, indoles and drugs3) Interconversions

a. Transamination (an interconversion): conversion of aa keto acid with simultaneous conversion of another keto acid aa; catalysed by transaminases; occurs in many tissues

Eg. Alanine + alpha-ketoglutarate pyruvate + glutamateb. Oxidative deamination (an interconversion): aa undergo dehydrogenation imino acid

hydrolysed to keto acid with production of NH4; occurs in liverEg. Aa + NAD+ imino acid + NADH + H

Imino acid + H20 Keto acid + NH4c. Ketogenic: leucine, isoleucine, phenylalanine, tyrosine; converted to ketone body

acetoacetated. Glucogenic: alanine and other aa’s; converted to compounds that can form glucose

4) Urea cycle: much NH4 produced by deamination in liver enters urea cycle carbamoyl phosphate citrulline in mitochondria arginine urea (formed in liver; so in liver disease decr BUN and incr NH3) excreted in urine

a. NB. Aa can also react with NH4 amide; or can convert NH4 NH3 (eg. In urine, NH3 reacts with H permitting it to be secreted)

5) Formation of creatine: made in liver from methionine, glycine and arginine; in skeletal muscle creatine reacts with ATP formed by glycolysis and oxidative phosphorylation ADP and phosphorylcreatine (which is important store of ATP, reversed during exercise); creatine shouldn’t be excreted in urine in normal men – marker of extensive muscle breakdown

6) Formation of creatinine: formed from phosphorylcreatine7) Formation of purines and pyrimidines: made in liver; combine with ribose to form nucleosides;

found in co-enzymes, DNA, RNA

Protein loss:1) Proteins lost : hair, menstruation, urine, stools2) Protein degradation : removal of abnormal/old protein

a. Conjugation of protein to ubiquitin tickets them for degradation (ubiquinitination) degraded in proteasomes / lysosomes; or tickets them for various destinations in cell

b. Uric acid formed by breakdown of purines excreted in urine via filtration 98% reabsorbed 80% secreted

Starvation:Low protein / normal calorie diet decr excretion urea and sulfates normal excretion creatine (wear-and-tear, not affected by diet)Low protein / low calorie diet insulin glucose attempts to spare protein (enough glycogen stores for

1/7 starvation; ie. 0.1kg in liver, 0.4kg in muscles) fats ketoacids attempt to spare protein ketosis (12kg fat)

protein catabolism (from liver, spleen, muscles) incr urea nitrogen excretion (urea and nitrogen formed)

Fat Metabolism

Fa’s (can be saturated – have double bonds; unsaturated – no double bonds), triglyceraides (3x fa’s bound to glycerol), phospholipids, sterolsEssential fa’s: linolenic, linoleic and arachidonic acids; polyunsaturated; arachidonic acid formed from tissue phospholipids by phospholipase A2

These are precursors of eicosanoids (PG’s, prostacyclin, TX, lipoxins, leukotrienes); formation inhibited by glucocorticoids which inhibit phospholipase A2, NSAID’s which inhibit COX’s; have short HL’s made via enzymes

COX: makes PG, prostacyclin, TXLOX: makes 5-HETE, 12-HETE, 15-HETE, lipoxins, LTCYP monooxygenases: make 12-HETE, EETs, DHTs

PG: PGH2 is precursor for PG’s, TXs and prostacyclin (converted by tissue isomerases); made from arachidonic acid by prostaglandin G/H synthases 1 and 2 (COX 1 and 2); COX1 constitutive, COX2 induced by GF’s, cytokines and tumour promoters; work via G proteins

TX: TXA2 made by plts promotes vasoC and plt aggregationProstacyclin: produced in endothelium promotes vasoDLeukotrienes: arachidonic acid converted to 5-hydroperoxyeicosatertraenoic acid (5-HPETE) by 5-lipoygenase leukotrienes (eg. Aminolipids – LTC4, LTD4, LTE4, LTF4); bronchoC, arterioC, incr vasc perm, chemotaxis; work via CysLT1 receptor broncoC, chemotaxis, incr vasc perm, CysLT2 pul vasc SM constriction; BLT chemotaxisLipoxin: A dilates microvasculature, B inhibits cytotoxic effects of NKC’s

Cellular lipids: 1) Structural lipids – part of membranes2) Neutral fat – stored in adipose cells; mobilized during starvation; make up 15% body weight in

men, 21% in women; adenylyl cyclase in adipose tissue activated by glucagons, NE + E via beta-3 receptor

3) Brown fat – more in infants; between scapulas, at nape of neck, along gt vessels; extensive SNS supply ( release of NE beta3-adrenergic receptors incr lipolysis, fa oxidation varies efficiency with which E produced and food utilized; incr nerve output when eating heat production); contain many droplets of fat and many mitochondria; normal oxidative phosphorylation occurs but also uncoupling of metabolism and generation of ATP so more heat produced (via uncoupling protein UCP1)

Plasma lipids: major lipids are insoluble in aqueous solutions hence aren’t free1) Free fatty acids: bound to albumin2) Lipoprotein complexes: cholesterol, triglycerides, phospholipids; complexes incr solubility of

lipids; generally contain hydrophobic core of triglycerides surrounded by phospholipids and protein (apoproteins – APO E,C,B)

Exogenous pathway: transports lipids from intestine to liver

1) Chylomicrons: formed in intestinal mucosa during absorption of products of fat digestion; very large lipoprotein complexes containing APO C; enter circ via lymphatics; cleared from circ by lipoprotein lipase in capillary endothelium (catalysed breakdown of triglyceride fa and glycerol enter adipose cells or enter circ bound to albumin) become chylomicron remnants which go to liver internalized by receptor-mediated endocytosis degraded in lysosomes

Endogenous pathway: transports lipids to and from tissues1) Very low density lipoproteins (VLDL): contain APO C; formed in liver; transport triG formed in

liver to other tissues2) Intermediate density lipoprotein (IDL): lipoprotein lipase removes triG from VLDL IDL; give

up phospholipids; pick up cholesteryl esters via lecithin-cholesterol acyltransferase3) Low density lipoprotein (LDL): when more triG lost; provide cholesterol to tissues (LDL taken up

by receptor-mediated endocytosis in clathrin coated pits endosome proton pumps in endosome decr pH inside endosome LDL receptor released and recycled endosome fuses with lysosome cholesterol made available inhibits production of intracellular chol by HMG-CoA reductase, stimulates esterification of XS chol, inhibits synthesis of new LDL receptors); LDL also taken up by macrophages (via scavenger receptor) esp LDL that has been modified by oxidation when become overloaded become foam cells

4) High density lipoprotein (HDL): take up chol from cells; made in liver and intestinal cells; transfer chol to liver where is excreted into bile

MetabolismTriG broken down by lipoprotein lipase as shown above (feeding INCREASES activity, fasting DECREASES activity), or hormone-sensitive lipase found intracellularily in adipose tissue (activity slowly INCREASED by GH, steroids and thyroid hormones and starvation via incr activity of cAMP; DECREASED activity by insulin and PGE and feeding by inhibiting formation of cAMP) fa enter cell or mobilize bound to albumin (provided to cell by chylomicrons and VLDL (used extensively in heart), or synthesized in depots) acetyl-CoA citric acid cycle (in mitochondria by beta-oxidation – serial removal of 2 C from fa with high yield of ATP compared to glu; medium and short chain fa can enter mitochondria easily, long-chain must be bound to carnithine to cross inner mitochondrial membrane – the linked pair then moved into matrix space by a translocase ester hydrolyse and carnithine recycled)

FormationAcetyl-CoA fa occurs in many tissues; occurs principally outside mitochondria

Ketone Body Formation Normal level 1mg/dLAcetyl-CoA acetoacetyl-CoA in many tissues acetoacetate in liver (a β-keto acid, a ketone body) β-hydroxybutyrate and acetone (ketone bodies; anions) enter circulation. Ketones normally metabolized as fast as formed: acetoacetate metabolized with CoA (from succinyl-CoA; and via other pathways) form CO2 and H20 via citric acid cycle (occurs in tissues other than liver)

If incr acetyl-CoA or decr supply of products of glu metabolism (eg. Starvation, DM, high-fat low carb diet, less can enter citric acid cycle acetoacetate accumulates ability of tissues to oxidize ketones exceeded ketosis anions so metabolic acidosis abolished by giving glu (hence carbs are antiketogenic)

Cholesterol Metabolism Normal level 120-200mg/dL

Precursor of steroid hormones and bile acids, important in cell membranes

Chol synthesis: shown in diagram; negative feedback by inhibiting HMG-CoA reductase; so when dietary intake high, hepatic synthesis inhibitedChol absorption: absorbed via chylomicrons after chylomicrons give up triG in adipose tissue chylomicron remnants bring chol to liver most incorporated in VLDL circulatesChol excretion: excreted in bile in free form and as bile acids some reabsorbed from intestine

Decr chol: thyroid hormones, oestrogens incr LDL receptors in liver, incr HDL levelsIncr chol: biliary obstruction, untreated DM

Trace Elements: essential for life; arsenic, chromium, cobalt, copper, fluorine, iodine, iron, manganese, molybdenum, nickel, selenium, silicon, vanadium, zincVitamin: organic dietary constituent necessary for life, health and growth that doesn’t supply E; vit E is bound to chylomicrons transferred to VLDL in liverB1 (thiamine, B complex) beriberi, neuritisB2 (riboflavin) glossitis, cheilosisNiacin pellagraPyridoxine convulsions, hyperirritabilityPantothenic acid dermatitis, enteritis, alopecia, adrenal insufficiencyBiotin dermatitis, enteritisFolates sprue, anaemia, NTDB12 (cycobalamin) pernicious anaemiaC scurvyD ricketsE ataxiaK haemorrhagic phenomena

ENDOCRINOLOGY

Thyroid Gland

Effect stimulates O2 consumption; regulate lipid and carbohydrate metabolismXS body wasting, nervousness, incr HR, tremor, XS heat productionLack mental and physical slowing, poor cold resistanceT3 = triiodothyronine; 25mcg daily production; 60% turnover per day; HL 1/7; 4x more potent; VOD 40LT4 = tetraiodothyronine / thyroxine; 75mcg/day daily production; 10% turnover per day; HL 7/7; VOD 10L

Anatomy: comes from evagination of floor of pharynx; 2 lobes connected by thyroid isthmus, occasional pyramidal lobe; high rate blood flow; made of multiple acini; follicles filled with colloid

Iodine: Normal plasma level 0.3μg/dLIngested iodine (500μg; min 150 needed; def when <50μg ingested) iodide absorbed (distributed in 25L)

thyroid (120μg/day) T3 and T4 (uses 80μg/day) secreted metabolized in liver and other tissues some secreted into bile some undergoes enterohepatic circulation, 20 μg/day lost in faeces

somes enters ECF (60 μg/day) enters ECF (40 μg/day) kidney excreted in urine

Enters thyroid via Na/I symporter (2Y AT) which transports into cells against electrochemical gradient for I; E provided from Na-K ATPase; a 2nd transport enzyme pendrin controls passage of I across membraneDeficiency: inhibits thyroid function, get goiter due to high TSHXS: inhibits thyroid function via Wolff-Chaikoff effect, inhibits binding of iodide transiently, reduces effect of TSH on thyroid by decr cAMP response, inhibits proteolysis of TG

Thyroid Hormone: Naturally occurring form is L-isomersThyroid cells: collected and transport iodine Make thyroglobulin (glycoprotein; made in thyroid cells; secreted into colloid by exocytosis

of granules that contain thyroid peroxidase (catalyses oxidation of iodide and its binding; can be blocked by v high I levels)) Remove thyroid hormones from TG (H bonds hydrolysed)

Iodide oxidized to iodine in thyroid bound to tyrosine residues of thyroglobulin forming MIT and DIT (iodide organification) thyroid hormones remain bound to TG until secretion into colloid

Thyroid hormone synthesis: monoiodotyrosine (MIT) iodinated to diiodotyrosine (DIT) 2 DIT’s + TG (oxidative condensation (coupling reaction) involing thyroid peroxidase) T4 1 DIT and 1 MIT T3 or RT3

Thyroid hormone secretion: 80μg T4, 4μg T3, 2μg RT3 secerted; MIT and DIT NOT secretedThyroid cells ingest colloid by endocytosis merge with lysosomes proteases break bonds between iodinated residues and TG T3, T4, DIT, MIT liberated into cytoplasm of cell MIT and DIT deiodinated by iodotyrosine deiodinase free I reutilized by gland

T3 and T4 enter circ (ratio of T4:T3 5:1)

Thyroid hormone transport: T4 = 8μg/dL (free 2; HL 6-7/7; VOD 10L)T3 = 0.15μg/dL (shorter HL, more rapid action)

Both bound to p proteins (99.98% T4 in plasma is bound mostly to TBG; T3 99.8% bound – 46% to TBG, rest to albumin)

Albumin (has largest capacity to bind T4; 13/7)Transthyretin (HL 2/7)Tyroxine binding globulin (TBG; has smallest capacity to bind T4 and yet most T4 bound to this; HL 5/7; incr by pregnancy and certain drugs; decr by glucocorticoids, androgens)

Thyroid hormone metabolism: T4 and T3 deiodinated (by deiodinases D1,2,3) in liver, kidney, other tissues; some T3 and 4 further deiodinated to deiodotyrosines conjugated in liver to sulfates and glucuronides bile (some enterohepatic circ) stool 4% daily I loss

T4: 1/3 converted to T3, 45% converted to RT3 (metabolically inactive)D1: in liver, kidneys, thyroid, pituitary; responsible for T34 in peripheryD2: in brain, pituitary, brown fat; responsible for T34 in those organsD3: in brain and reproductive tissues; main source of RT3

Illnesses may suppress deiodinases ( incr RT3, decr T3) eg. Burns, trauma, Ca, cirrhosis, renal failure, MI, fasting, amiodarone, beta blockers, corticosteroidsTriiodothyronin (T3): 13% release from thyroid, 87% formed from deiodination of T4; more active than T4 – more rapid, 3-4x more potent as less tightly bound to plasma proteins and more acid binding to TRReverse triiodothyronine (3,3’,5’-triiodothyronine, RT3): inactive; 5% secreted by thyroid, 95% by deiodination of T4; more prominent in fetus

Mechanism of Action: TSH works via GPCREnter cells via AT (affinity for T4 receptor less than T3, explaining potency) T4 deiodinated to T3 T3 binds thyroid receptors (TRα1 and 2; TRβ1 and 2) in nuclei hormone-receptor complex binds DNA alter gene expressionCan get mutation of TRβ T hormone resistance; clinically euthyroid as TRα OK, but high TSH

Regulation of Release: TRH: from hypothalamus; secreted into capillaries of pituitary portal venous system pituitary gland mediates incr secretion due to cold; inhibited by stressTSH: glycoprotein; from APG; made of subunit α and β; HL 60mins; degraded in liver and kidneys; peak secretion at midnight; ave level 2μU/mL

incr iodide binding; synthesis of T3, T4, MIT, DIT; secretion of TG into colloid; endocytosis of colloid; incr blood flow; chronic causes cell hypertrophy and goiter- inhibited by dopamine, somatostatin, glucocorticoids

TSH receptor: on thyroid cells; serpentine; activates Gs adenylyl cyclase and PLC \NB. Thyroid cells also have receptors for IGF-1, EGF and other GF’s

Homeostasis: when sudden incr bind proteins decr free hormone incr TSH incr release hormoneThyroid also regulates own uptake of iodide independent of TSH

Effects of Thyroid Hormones:Metabolism incr O2 consumption (calorigenic action) (EXCEPT in brain, testes, uterus, LN, spleen,

APG); will cause vitamin def incr DPG (incr dissociation of O2 from Hb)

incr activity of Na-K ATPases decr circulating chol levels

Heart chonotropic, inotropic; incr no β receptors, enhanced response to E+NE incr HR and PP generation of heat decr PVR as heat dissipating mech renal Na and H20 retention altered expression of myosin heavy chain (more α, which has higher ATPase activity) incr

speed of cardiac contractionAdipose tissue catabolic (incr lipolysis)Muscle catabolic (incr protein breakdown) will cause K release which is excreted in urine; also

thyrotoxic myopathy, muscle weakness, cramps, stiffnessBone incr growth and skeletal developmentCNS incr brain development rapid mentation, irritability, restlessness; incr responsiveness to E+NE activated RAS hyperreflexiaGut incr carb absorptionLipoprotein incr formation of LDL receptors

Symptoms:HypoT: hypoT: no response to TSH pituitary hypoT: thyroid responds to TSH Hypothalamic hypoT: thyroid responds to TSH; incr TSH following dose of TRH

myxoedema (skin contains polysaccharide, hyaluronic acid, chondroitin sulfuric acid which accumulate) decr BMR coarse sparse hair Yellow skin: carotenemia due to accum of carotene in skin (as T needed for hepatic conversion of carotene to vit A) poor cold tolerance slow husky voice slow mentation, poor memory incr plasma chol cretinism (dwarf, mental retardation, potbellies, large tongue, deaf mute, rigidity

HyperT: Grave’s disease (60-80%; autoimmune; antibodies to TSH receptor stimulate receptor; TSH Low; also ab to TG and thyroid peroxidase)Hashimoto’s thyroiditis (ab destroy thyroid, but during early inflamm XS secretion)Toxic adenoma / multinodular goiter, TSH-secreting APG tumour, mutations of TSH receptor, ectopic thyroid tissue nervous weight loss hyperphagia heat intolerance incr PP fine tremor warm soft skin sweating incr BMR exophthalmos (adipocytes in orbits have TSH receptor release cytokines inflammation and oedema)

Pancreas

Glucose:

Enters cells by facilitated diffusionGLUT 1: in placenta, BBB, brain, RBC, kidneys, colon; basal uptake; transport across BBBGLUT 2: B cell glu sensor; in B cells, liver, SI, kidneys; transport OUT of intestine and renal epithelial cells; regulation of insulin releaseGLUT 3: in brain, placenta, kidneys; basal uptake inc into neuronsGLUT 4: in skeletal and cardaic muscle, adipose tissue; insulin-sensitive uptake of gluGLUT 5: in jejunum and sperm; fructose transportGLUT 6: GLUT 7: in liver; G6P transporter in ER

2Y AT with Na SGLT 1 – in small intestine and renal tubulesSGLT 2 - in renal tubules

On entering cell, glu phosphorylated

Anatomy: Islets of Langerhans: in pancreas, more in tail; make up 2% of gland; 1-2 million islets; blood drains into hepatic portal vein; involved in paracrine regulation

A cells: secrete glucagon from granules; make up 20% of cells; surround B; stimulates release of insulin and somatostatinB cells: secrete insulin from granules; account for 60-75% of cells; in centre of islet; inhibits release of glucagon

Respond to stimulation via hypertrophyProlonged stimulation (eg. XS GH or T hormone) B cell exhaustion transient then

permanent diabetesD cells: secrete somatostatin from granules; inhibits release of insulin, glucagon and PPF cells: secrete pancreatic polypeptide

Insulin: Glycogenesis, antigluconeogenesis, antilipolysis, antiketoticIGF-I and IGF-II responsible for nonsuppressible insulin-like activity - weak

Synthesis: preproinsulin has peptide removed as enters RER of B cells, molecule folded and disulfide bonds formed proinsulin containing A and B chain, connected by connecting (C) peptide transported to GA packaged into granules transport of granules via microtubules, during which C peptide removed, proteases involved in processing insulin formed (Polypeptide – 2 chains of aa linked by disulfide bridges) exocytosis of 90-97% insulin, some C peptide, rest proinsulin into blood

Metabolism: HL 5 mins; binds to insulin receptors; destroyed by proteases in endosomes formed by endocytosis in liver (60%) and kidney (35-40%) (this ratio is reversed in diabetics receiving insulin, where renal metabolism is more important)

Mechanism of action: Insulin receptor: found on most tissues; made of 2α (extracellular, bind insulin) and 2β (intracellular portions have tyrosine kinase activity) glycoprotein subunits bound by disulfide bonds; on binding to receptor, complex undergoes endocytosis complex enters lysosome recycled; HL 7hrsInsulin binds receptor triggers tyrosine kinase activity of β subunits autophosphorylation of β subunits (ie. They come close together and phosphorylate eachother) phosphorylation/desphosphorylation of cytoplasmic proteins

1) Activated phosphoinositol-3 kinase vesicles containing GLUT 4 fuse with cell membrane; incr glycogen synthase activity, incr glycogen formation, enhanced cell growth and division, other metabolisc effects

2) Activated glucokinase (in liver) incr phosphorylation of intracellular glu decr free glu conc intracellularily incr glu influx

3) Causes K to enter cells due to incr activity of Na-K ATPase decr extracellular K

Regulation of secretion: Normal insulin 0-70μU/mL (basal - 1μU/hr)

Fast response: Glu enters B cells by GLUT 2 transporter phosphorlyated to glucokinase metabolized to pyruvate in cytoplasm enters mitochondria and Kreb’s cycle release of ATP which enters cytoplasm inhibition of ATP-sensitive K channels decr K efflux depolarization of B cell Ca influx through voltage-gated Ca channels exocytosis of insulin-containing granules initial insulin spikeSlow response: pyruvate from above Kreb’s cycle incr intracellular glutamate commits another pool of granules to release prolonged 2nd phase

Insulin release stimulated: Glu, mannoseaa’s (eg. Arginine, leucine) - amplify glu-induced insulin releaseβ-ketoacids (eg. Acetoacetate) these release ATP which inhibit K channels mentioned aboveBeta-agonists, glucagon, theophylline incr cAMP in B cells incr Ca (amplify glu-induced insulin release)Vagal stimulation and Ach M4 receptors incr CaGlucagon, secretin, CCK, gastrin, GIP – amplify glu-induced insulin releaseSulphonylureas

Incr affinity of insulin for receptor: GH, GC

Inhibited insulin release: SNS NE acting on α2-receptorsK depletion (eg. Thiazide diuretics)SomatostatinPhenytoin, diazoxide, vinblastin, colchicine

Effects: Anabolic; incr storage of glu, fa, aa incr no glu transporters in cell membrane

Rapid (sec): incr transport of glu, aa and K into insulin-sensitive cellsIntermediate (min): stimulation of protein synthesis

Inhibition of protein degradation Activation of glycolytic enzymes and glycogen synthase Inhibition of phosphorylase and gluconeogenic enzymes

Delayed (hrs): incr mRNA’s for lipogenic and other enzymes

Adipose tissue: Incr glu entryIncr fa synthesis and triG depositionIncr glycerol phosphate synthesisActivation of lipoprotein lipase (responsible for uptake from plasma)Inhibition of hormone-sensitive lipase (responsible for catabolism)Incr K uptake

Muscle: Incr glu entryIncr glycogen synthesis (induces glycogen synthase and glucokinase)Incr aa uptake and protein synthesis in ribosomesDecr protein catabolism and release of gluconeogenic aaIncr ketone uptakeIncr K uptake

Liver: Decr ketogenesis / glycogenolysis / gluconeogenesis decr glu outputIncr protein synthesisIncr lipid synthesisIncr glycogenesis (induces glucokinase and glycogen synthase)

Defiency: decr peri utilization – decr entry of glu into cells (except in brain and RBC where OK) deranged glucostatic function of liver with incr release – decr glycogen synthesis, incr glu output

EXTRACELLULAR GLU XS

polyuria (osmotic diuresis) polydipsia (dehydration) weight loss glycosuria incr HbA1c (when prolonged hyperG, HbA glycated)

INTRACELLULAR GLU DEF incr lipolysis (to supply E needs of cell) incr action of hormone-sensitive lipase incr free fa’s and triG’s decr lipogenesis: due to intraC glu def; decr removal of triG, fa and chylomicrons from blood due to decr activity of lipoprotein lipase

incr fa and triG catabolised to AcoA some enters Kreb’s cycle CO2 + H20

rest cannot enter Kreb’s cycle for conversion to fa as depleted AcoA carboxylase XS AcoA converted to acetoacetyl-CoA acetoacetate, acetone, β- hydroxybutyrate (ketone bodies; source of E) formed in liver anions of

strong acids buffering capacity exceeded ketosis, acidosis NB. Cations lost with anions in urine hypoNa and K

incr protein catabolism to C02 and H20 and glu via incr gluconeogenesis decr entry of aa into muscle (decr protein synthesis so maintained supply of aa for

gluconeogenesis) incr activity of various enzymes in Kreb’s cycle / glycolysis (ie. Phosphoenolpyruvate carboxykinase, F1,6-DPase, G6Pase, pyruvate carboxylase) glycogen depletion hyperphagia due to decr glu in satiety area of hypothalamus coma (may be due to acidosis / dehydration; may be hyperosmolar)

CHRONIC EFFECTS: intracellular hyperG activation of enzyme aldose reductase incr formation of sorbitol in cells decr Na-K ATPase; intracellular glu converted to advanced glycosylation end products (AGEs) crosslink matrix proteins damage BV’s

XS: hypoG; glu only source of fuel for brain, which has poor carbo reserves Complete inhibition of insulin secretion at 80mg/dL glu Incr secretion of glucagon and E incr glycogenolysis by liver Incr secretion of GH and cortisol decr glu utilization peripherally

Palpitations, nervous, sweating (due to autonomic discharge; if not present – hypoglycaeamia unawareness) hunger, confusion lethargy, coma, convulsions, death

Insulin resistance; incr BMI; decr lipogenesis and muscle genesis, incr gluconeogenesis; hyperinsulinaemia and dyslipidaemia = metabolic syndrome / syndrome X

Glucagon Glycogenolysis, gluconeogenesis, lipolysis, ketogenesisNormal insulin:glucagon is 2.3; catabolic; mobilizes glu, fa, aa

Synthesis: preproglucagon found in A cells, L cells in lower GI tract and brain in A cells processed to glucagon and major proglucagon fragment (MPGF) secreted into portal vein in L cells processed to glicentin – has some glucagon activity

glucagon-like polypeptides 1 and 2 (GLP-1 and 2) – have no activity but processed to GLP-1 (7-36) which stimulates insulin secretion and glucose use

oxyntomodulin – inhibits gastric acid secretion in A and L cells residual glicentin-related polypeptide (GRPP) is left (has no activity)

Metabolism: HL 5-10mins; degraded by liver (which is reaches 1st via portal vein so low systemic levels)

Regulation of Secretion:

Stimulators: low glu, aa’s (eg. High protein meal – prevents hypoG while insulin allows storage of glu), CCK, gastrin, cortisol, exercise, infections, stress, beta-agonists (beta-receptors mediators of SNS supply), theophylline, AchInhibitors: glu, somatostatin, secretin, fa, ketones, insulin, phenytoin, alpha-agonists, GABA effect on A cells (via GABAa receptors which are Cl channels and allow Cl influx that hyperpolarize A cells)

Effects: Incr blood sugar levelActs on serpentine receptors incr plasma glu

In liver: via Gs adenylyl cylase incr intracellular cAMP PKA activation of phosphorylase glycogenolysis inhibit conversion of phosphoenolpyruvate to pyruvate inhibit conversion of F6P to F1,6DP

via different receptor activation of PLC incr cytoplasmic Ca glycogenolysisAlso: incr gluconeogenesis Incr ketone body formation by decr malonyl-CoA levels in liver Lipolysis No glycogenolysis in muscle Incr secretion of GH, insulin, pancreatic somatostatin

+ive inotropic effect on heart due to incr cAMP

Somatostatin:Found in D cellsRelease stimulated by: glu, aa, CCK

Action: inhibit secretion of insulin, glucagon, and pancreatic polypeptide in a paracrine fashionEffect: hyperG and (due to low CCK) slowed gastric emptying, decr gastric acid secretion, gallstones

Pancreatic Polypeptide:Release stimulated by: fasting, exercise, acute hypoGRelease inhibited by: somatostatin, IV gluEffect: slowed absorption of food

Exercise:Incr GLUT 4 transporters in muscle cell membranes (insulin independent) incr entry glu into skeletal muscle can cause hypoG

Catecholamines:1) Initial glycogenolysis: activation of phosphorylase in liver via beta-receptors incr intracellular cAMP

Via alpha-receptors incr intracellular Ca incr hepatic glu output hyperG

2) Then glyocgenesis: activation of phosphorylase in muscle via actions above incr formation G6P incr pyruvate converted to lactate enters circ oxidized in liver to pyruvate converted to glycogen3) Other effects: incr fa

Thyroid Hormone: exacerbates diabetes as incr absorption of glu from SI and enhance glycogenolytic effect of catecholamines

Glucocorticoids: exacerbate diabetes via causing gluconeogenesis in liver, incr hepatic glycogenesis and ketogenesis, decr peri glu utilization

GH: exacerbates diabetes via mobilization of fa from adipose tissue, decr glu uptake into tissues, inr hepatic glu output, decr tissue binding of insulin

Adrenal Glands

AnatomyBlood supply from renal, phrenic and aortic arteries – large blood flow

Medulla: 28% mass; granule-containing cells near venous sinuses; densely innervated; 2 cells types:E-secreting type: larger, less dense granules; 90%NE-secreting type: smaller, dense granules; 10%

Secretes E (more important in humans), NE, D; secretion stimulated by preganglionic nerve fibres via splanchnic nerves

Cortex: cells contain large amount of SER; secretes steroid hormones; secretion contolle by ACTH (G) and AII (M) – glucocorticoids (metabolism of carbs and protein), mineralocorticoids (maintenance of Na balance and ECF vol) and sex hormones Outer zona glomerulosa (15% overall mass) – secrete corticosterone and aldosterone; also

important in formation of new cortical cells which replenish the inner layers Inner Zona fasciculata (50%) – columns of cells; secrete corticosterone, cortisol > sex hormones Inner zona reticularis (7%) – continuous with inner ZF; secrete corticosterone, cortisol < sex

Hormones

Catecholamines

Synthesis:NE: formed by hydroxylation and decarboxylation of tyrosineE: formed by methylation of NE (catalysed by phenylethanolamine-N-methyltransferase (PNMT), induced by glucocorticoids which are in high conc in adrenal vein)D: 50% comes from medulla, 50% from ANSStored in granules with ATP and chromogranin AAlso made in adrenal medulla: metenkephalin, adrenomedullin

Regulation of secretion: Ach from preganglionic neurons opens cation channels Ca influx from ECF exocytosis of granulesIncr release: incr SNS; familiar stree incr NE, unexpected stress incr EDecr release: sleep

Metabolism: enter plasma 95% dopamine, 70% E and NE conjugated to sulphate (inactive) HL 2mins methoxylated 50% occurs in urine as free/conjugated metanephrine and normetanephrine

35% occur in urine as 3-methoxy-5-hydroxymandelic (vanillymandelic) acid (VMA) (700 μg/day)

small amount of free E (6 μg/day) or NE (30 μg/day)

Mechanism of Action: work of alpha and beta receptors

Effects: Mostly mediated through E in physiological circumstancesMost of effects of NE are through local release from postganglionic sym neurons

Metabolic: glycogenolysis in liver and skeletal muscle (via beta-receptor cAMP and phosphorylase) (via alpha-receptor Ca)

Incr secretion isulin and glucagons (via beta-receptor; decr secretion via alpha-receptor) Lipolysis fa Incr plasma lactate Incr BMR (may be due to cut vasoC incr temp; incr muscle activity; oxidation of lactate in liver)

Cardiac: positive inotrope and chonotrope (via beta1-receptor)Incr myocardial excitabilityNE VasoC in most organs (via alpha1-receptor)

E vasoD in skeletal muscle and liver (via beta-2 receptor) net decr PVRNE alone incr BP but reflex bradycardia with decr COE alone widened PP, incr HR and incr CO (due to insufficient reflex)

CNS: incr alertness; anxiety and fearOther: incr K due to release from liver then prolonged decr K due to incr entry into skeletal muscleDopamine: renal vasoD; vasoD in mesentry; vasoC elsewere via release of NE; +ive inotrope via beta1-receptors; natiuresis by inhibition of renal Na-K ATPase; net incr SBP

Cortical HormonesMade from chol

C19 steroids: androgenic – dehydroepiandrosterone (DHEA), androstenedione (most oestrogens made from this)

C21 steroids: mineralocorticoids – aldosterone, deoxycorticosterone (on 3% activity of aldosterone); 9α-fluorocortisol has mineralocorticoid activity

Glucocorticoids – cortisol (10-20mg/day in normal adult), corticosterone (7:1 ratio); prednisone and dexamethasone have glucocorticoid activity

Synthesis: 1) Acetate / uptake from LDL in body cholesterol esterified and stored in lipid droplets transported to mitochondria by sterol carrier protein 2) In mitochondria converted to pregnenolone (catalysed by cholesterol desmolase / side-chain cleavage enzyme / P450scc / CYP11A1 – CP450 member)

Pregnenolone 17α-hydroxypregnenolone (catalysed by 17α-hydroxylase / p450c17 / CYP17– CP450 member)

3) Pregnenolone moves to SER dehydrogenated to progesterone (catalysed by 3β-hydroxysteroid dehydrogenase – NOT a CP450 member; this enzyme more active in ZF)

Progesterone 17α-hydroxyprogesterone (catalysed by 17α-hydroxylase)NB. 17α-hydroxypregnenolone can be converted to 17α-hydroxyprogesterone (catalysed by 3β-hydroxysteroid dehydrogenase)

4) In SER: Progesterone hydroxylated to 11-deoxycorticosterone (catalysed by 21β-hydroxylase / P450c21 / CYP21A2 – a CP450) 17α-hydroxyprogesterone hydroxylated to 11-deoxycortisol (catalysed by 21β-hydroxylase)5) 11-deoxycorticosterone and 11-deoxycortisol move back to mitochondria IN ZONA FASCICULATA/RETICULARIS hydroxylated to corticosterone and cortisol (catalysed by 11β-hydroxylase / P450c11 / CYP11B1 – a CP450)IN ZONA GLOMERULOSA catalyst aldosterone synthase / p450c11AS / CYP11B2 is present aldosterone formed (no 11β-hydroxylase or 17α-hydroxylase in ZG)

NB. 17α-pregnenolone and 17α-progesterone C19 steroids dehydroepiandrosterone and androstenedione (catalysed by 17,20-lyase; this enzyme more active in ZR therefore makes more androgens)

androstenedione converted to testosterone and oestrogens in fat and other peri tissues (important in postmenopausal women)

Deficiencies: 17α-hydroxylase – rare; no sex hormones produced so female genitalia; can still make mineralocorticoids so get hyperT and hypoK; def cortisol but can still make corticosterone and aldosterone

21β-hydroxylase – common; decr production cortisol and aldosterone incr ACTH; steroids converted to androgens virilisation; def in aldosterone hypoNa and hypoV

11β-hydroxylase – virilisation, but hyperT

Regulation of release:

Glucocorticoid:

ACTH (HL 10mins) binds to receptors on adrenocortical cells Gs adenylyl cyclase incr formation pregnenolone and derivatives release of hormones (inc androgens); ACTH increases sensitivity of adrenal to further release of ACTHACTH released in circadian rhythm (peak in morning); governed by biologic clock in suprachiasmatic nuclei of hypothalamusDecr ACTH release: free GC’s (also decr adrenal responsiveness to ACTH) – inhibition at pituitary and hypothalamic levelIncr ACTH release: stress (there is a ceiling at which incr ACTH no longer incr release of GC); incr due to incr CRH from paraventricular nuclei in hypothalamus transported through portal-hypophysial vessels to APG; multiple inputs to hypothalamus from emotional stress / pain etc…

Mineralocorticoid: ACTH can stimulate MC release, but effect is transientRenin (from JG cells surrounding renal afferent arterioles which notes drop in ECF vol) activates angiotensinogen conversion of angiotensin I to II AII binds to AT1 receptors in ZG G protein activation of PLC incr PKC

incr chol converted to pregnenolone incr conversion of corticosterone to aldosterone (helps action of aldosterone synthase)

K stimulates conversion of chol to pregnenolone, and of deoxycorticosterone to aldosteroneWorks via depolarizing cell opens voltage-gated Ca channel incr intracellular CaHence low K diet decr sensitivity of ZG to AII

ANP inhibits renin secretion decr responsiveness of ZG to AII

Conc of dehydroepiandrosterone sulphate higher in young men than old, due to altered activity of lyase activity

Incr release GC and MC: surgery, anxiety, physical trauma, haemorrhageIncr release MC only: hyperK (small incr needed), hypoNa (large drop needed), constriction of IVC in thorax (decr intrarenal p), standing

Plasma Binding: bound steroids are inactive; bound acts as reservoirCortisol: 90% bound to transcortin / corticosteroid-binding globulin (CBG) (synthesized in liver;

production increased by oestrogen – incr in pregnancy and hyperthyroidism; decr in cirrhosis, nephrosis; if incr more cortisol incr ACTH incr cortisol secretion until normal free level, so high total level without symptoms of XS)

Albumin (minor; 5%; large capacity but low affinity); 5% freeStronger bound than corticosterone so longer HL (60-90mins); very little free; binding saturated at 20μg/dL; total amount 13.5μg/dL

Corticosterone: similar to above, but lesser extent HL 50mins

Aldosterone: slight protein binding; HL 20mins (short); total level 0.006μg/dL

Metabolism:Cortisol: in liver (similar for cortisone except not step 3); rate decreased in liver disease and stress

1) Cortisol reduced dihydrocortisol tetrahydrocortisol conjugated to glucuronic acid2) 20% Cortisol cortisone (catalysed by 11β-hydroxysteroid dehydrogenase type 1 and 2) this

is active but promptly reduced and conjugated to tetrahydrocortisone glucuronide3) 1/3 Cortisol 17-ketosteroid version conjugated to sulphate

conjugates freely soluble enter circ and bind to p proteins excreted in urine, by tubular secretion (only 1% excreted unchanged) 15% excreted in stool (may under enterohepatic circ)

Aldosterone: 1) Converted in liver to tetrehydroglucuronide derivative 2) Converted in liver and kidneys to 18-glucornide derivative (will be converted to free aldosterone

in v acidic pH) excreted in urine 1% free form, 5% form 2, 40% form 3

Mechanism of action:Glucocorticoids: bind to glucocorticoid receptors (which when not bound are complexed with Hsp90 binding causes dissociation of Hsp) AT to nucleus complexes act as transcription factors (binds to GC receptors elements (GRE) in genes) synthesis of enzymes which alter cell function; hGRα is active receptor; hGRβ is inactive form capable of inhibiting GC’s; proteins called coregulators / corepressors help/inhibit interaction of GRE’s with receptorMineralocorticoids: bind to cytoplasm receptor (eg. Principle cell in renal tubules) complex moves to nucleus altered transcription of mRNA’s incr protein production incr activity of epithelial Na channel (ENaC) via incr insertion of channel in cell membranes, incr synthesis of channel, incr serum and glucocorticoid-regulated kinase incr activity of Na-K ATPase

NB. GC’s can bind to MC’s receptors; hence MC-sensitive tissues contain enzyme 11β-hydroxysteroid dehydrogenase type 2 which converts cortisol cortisone 11-oxy derivative which is not active at receptor; if this enzyme is absent, GC have MC effects

Effects:Androgens: adrenal androgens only have 20% effect of testosterone

masculinising effects (little effect unless in XS amount) promote protein anabolism and growth

Glucocorticoids: overall catabolicincr protein catabolism incr aa

Incr hepatic glycogenesis and gluconeogenesisIncr G6Pase activityIncr plasma glu level incr insulin release (which stimulates lipogenesis, so net deposition of fat with incr fa and glycerol in circ)Incr lipid levels (lipolysis) and ketone body formationPermissive action: small amounts vital for certain reactions to occur (ie. Needed for metabolic action of glucagon and NE+E, vascular reactions of NE+ENeeded for effective H20 excretionEncourage sequestration of eosinophils in spleen and lungs; decr basophils; incr neutrophils, plts and RBC’s; decr lymphocyte count; decr secretion of cytokines; inhibit inflamm response; inhibit macrophages and APC’s; decr PG, LT and PAF synthesis, and COX2; suppress mast cell degranulation; decr histamine release from basophils and mast cells decr cap permeability; no effect on ab’s at mod doses

Deficiency altered H20, carb, protein, and fat metabolism; fasting hypoGXS Cushing’s syndrome; will be protein depleted; thin skin, poor muscles, poor wound healing, easy bruising, thin hair, central fat distribution, buffalo hump, striae, hyperG, hyperlipidasemia, ketosis; may get mineralocorticoid action from v high GC salt and H20 retention moon face, K depletion, weakness; may get hyperT; bone dissolution OP; incr appetite, insomnia, psychosis; chronic XS decr ACTH, GH, TSH, LH; antagonize effect of Vit D on Ca absorptionNB. Corticosterone exerts minor MC effect

Mineralocorticoids: incr reabsorption of Na from urine (via action on principal cells in CD K diuresis), sweat, saliva, colon Na retention (takes 10-30min to develop); Na exchanged for K and HDeficiency hypoNa, hypoV, hyperKXS (eg. Conn’s; 2Y due to cirrhosis, heat failure, nephrosis) hyperNa but also hyperH20 so Na level normal, hyperV incr BP, hypoK; H lost in urine; weakness, tetany, polyuria, hypokalaemic alkalosis

Escape phenomenon: still get urinary loss of Na due to incr secretion of ANP; this prevents Oedema

NB. Deoxycorticosterone is precursor of aldosterone; HL 70mins; control of secretion related to ACTH

Calcium Metabolism

Calcium Normal plasma level 10mg/dL; 2.5mmol/LNormally ingest 600-1000mg/day (absorb 100-250mg/day)

Absorption: Active tranposrt out of SI via Ca-dependent ATPase (increased by 1,25dihydroxycholecalciferol; incr Ca decr 1,25DHCC so absorption indirectly proportionate to dietary intake Some passive diffusion

Distribution99% Ca sequestered in skeleton

Readily exchangeable reservoir – small; 500mmol/day moves in and outSlowly exchangeable reservoir – large; involves bone resorption and deposition; only 7.5mmol/day moves in and out

1% Ca free – important for 2nd messenger, coagulation, muscle contraction, nerve function some bound to p protein (proportionate to p protein level; incr binding at high pH) is filtered by kidneys but 98-99% reabsorbed (60% in PCT, rest in aLOH and DCT; DCT regulated by PTH)

Deficiency: hypocalcaemic tetany via excitatory effect on nerve and muscle cells; may cause fatal laryngospasm\98% filtered Ca reabsorbed by kidney

Phosphate Normal plasma level 12mg/dLFound in ATP, 2,3-DPG, proteins

Absorption: absorbed in duodenum and SI by AT and passive diffusion; absorption proportionate to dietary intake; incr absorption by 1,25dihydroxycholecalciferol

Distribution85-90% in skeletonRest free – is filtered in glomeruli 85-90% reabsorbed (2Y to AT in PCT; this AT is inhibited by PTH)2/3 is in organic compounds; 1/3 in PO4, HPO4, H2PO485% filtered phosphate reabsorbed by kidney

Vitamin D Are secosteroids

Synthesis:7-dehydrocholesterol sun previtamin D3 (rapid) slow development of Vit D3 (cholecalciferol) (can also be ingested in diet) transported in plasma bound to vitamin D-binding protein (DBP) (has lower affinity for 1,25 (hence more rapid clearance) than for 25, and 24,25

Metabolism:In liver, cholecalciferol converted to 25-hydroxycholecalciferol (calcidiol, 25-OHD3) (normal level 30ng/mL) in PCT of kidneys converted to 1,25-dihydroxycholecalciferol (calcitriol, 1,25-(OH)2D3 (catalysed by 1α-hydroxylase; normal level 0.03ng/mL; also made in keratinocytes in skin, placenta, macrophages) in kidneys 24,25-dihydroxycholecalciferol also formed

Regulation of synthesis: of 1,25-dihydroxycholecalciferolIncr formation: caused by PTH (low Ca incr PTH); low PO4Decr formation: decr PTH (high Ca negative feedback on PTH); high PO4 (inhibits 1α-hydroxylase); 1,25-dihydroxycholecalciferol (which also inhibits 1α-hydroxylase, encourages formation of 24,25-dihydroxycholecalciferol, inhibits formation of PTH)

24,25-dihydroxycholecalciferol formed instead

Mechanism of Action:1,25-dihydroxycholecalciferol binds receptor exposes DNA-binding region altered transcription

formation of calbindin-D proteins (calbindin-D9k and D28k) incr Ca transport incr no Ca-H ATPase molecules in intestinal cells incr Ca transport

Effects: of 1,25-dihydroxycholecalciferol Incr Ca and phos for formation of bone incr Ca absorption in SI incr reabsorption of Ca in kidneys (25 more potent) incr synthetic activity of osteoblasts (with 2Y incr activity of osteoclasts) regulates PTH release, insulin release, cytokine production by macrophages and T cells

Deficiency: rickets / osteomalacia; bowed bones, dental defects, hypoCa

PTH Normal plasma level 10-55pg/mLHL 10mins

Anatomy: 4 glands embedded in thyroid; chief cells make and secrete PTH; also contain oxyphil cells function of which unknown

Synthesis: preproPTH made enters ER aa removed proPTH removal of more aa in Golgi apparatus PTH packaged into secretory granules and released from chief cells

Metabolism: rapidly cleaved by Kupffer cells in liver into biologically inactive fragments cleared by kidney; HL few mins

Mechanism of action: 1) hPTH/PTHrP receptor: binds PTH and PTH-related protein (PTHrP; marked effect on growth and development of cartilage in utero; involved in Ca transport in placenta); serpentine receptor coupled to Gs adenylyl cyclase incr cAMP; also activated PLC via Gq incr intracellular Ca PKC2) PTH2 receptor: in brain, placenta and pancreas; binds PTH; serpentine receptor coupled to Gs adenylyl cyclase incr cAMP3) CPTH receptor: binds PTH

Regulation of Secretion:Ca binds calcium sensing receptor (CaR); incr phos binds free Ca decr level of free Ca incr PTHIncr secretion: low Ca; incr phosphate (which causes low Ca and inhibits formation of 1,25DHCC)Decr secretion: incr Ca (cell membrane serpentine Ca receptor coupled via G protein to phosphoinositide turnover inhibits PTH secretion); 1,25DHCC decreases preproPTH via decr gene transcription; ow Mg; low PTH Ca deposited in bones

Effects: Incr Ca level by bone resorptionDecr plasma phosphate

incr bone resorption (incr activity and no of osteoclasts) incr phosphate excretion in urine (decr reabsorption phosphate at PCT) incr Ca reabsorption in DCT (decr reabsoprtion of phos, aa, HCO3, Na, Cl, SO4) incr formation of 1,25DHCC incr absorption Ca at SI stimulates osteoclasts and osteoblasts in longterm suppresses further formation of PTH

Deficiency: low Ca NM hyperexcitability hypoCa tetany (Chvostek’s sign, Trousseau’s sign); high phosphateXS: hyperCa, hypophosphataemia; may get kidney stones

CalcitoninSecreted from parafollicular cells of thyroid; HL 10mins

Regulation of secretion: incr release by beta-agonists, dopamine, oestrogens, gastrin, CCK, glucagons, secretinMechanism of action: serpentine receptors in bone and kidney

Effect Decr Ca and phos as all entering bone: Inhibits bone resorption (inhibits activity of osteoclasts) decr Ca and decr phos increases Ca and phos (and Na, K, Mg) excretion by kidney incr secretion of Na, K, Cl and H20 into gut; decr release of gastrinMay protect pregnant bone, prevent postprandial hyperCa, have role in skeletal maturation

OthersOestrogen: inhibit secretion of cytokines (eg. IL-1, IL-6, TNFα) which aid development of osteoclasts decr breakdown of bone; inhibit bone resorbing effects of PTHGC’s: lower Ca by inhibiting osteoclast formation and activity, but cause OP over longterm (decr bone formation by inhibiting osteoblasts, incr bone resorption); decr absorption of Ca and phos from SI; incr renal excretion of Ca and phosGH: incr Ca ecretion in urine; incr intestinal absorption of Ca; resultant incr CaIGF-1: incr protein synthesis in boneThyroid: incr CaInsulin: incr bone formation

Pituitary Gland

AnatomyPPG: endings of axons from supraoptic and paraventricular nuclei of hypothalamus on BV’s; contains pituicytes

APG: connected to brain via portal hypophysial vessels; made up of interlacing cells (containing granules of stored hormone) and network of sinusoidal fenestrated capillariesContain chromophilic cells – can be acidophils / basophils; secretory

1) Somatotropes – secrete GH2) Lactotropes – secrete prolactin3) Corticotropes – secrete ACTH; POMC is hydrolysed in there cells for from ACTH and

β-LPH and β-endorphin which are secreted4) Thyrotropes – secrete TSH5) Gonadotropes – secrete FSH and LH

chromophobic cells – secretory; inactive with few granules

IPG: proopiomelanocortin (POMC) further hydrolysed to corticotropin-like intermediate-lobe peptide (CLIP; function unknown), γ-LPH (function unknown) and β-endorphin

Deficiency: decr adrenal GC’s and sex hormones (still some secretion); decr stress-induced incr aldosterone, but still some secretion so no H20 retention; decr growth; decr thyroid function; decr 2Y sex characteristics; tendancy to hypoG when fasted; decr ACTH decr protein catabolism decr osmotically active substrate in urine decr urine production (despite decr ADH);

GH 0.2-1.0mg/day output; basal level 0-3ng/mL in adults

Distribution: bound to p protein which is produced by cleavage of GH receptors; 50% bound

Metabolism: rapid, partly in liver; HL 6-20mins

Mechanism of action: large receptor has 2 binding sites for receptors (JAK/STAT cytokine receptor)– binds 1 subunit, attracts another subunit homodimer receptor activation activates intracellular

enzyme cascades (eg. JAK2-STAT pathway); possibly acts on cartilage to make stem cells that respond to IGF-I

Regulation of secretion: feedback controlIncr release: GHRH from hypothalamus; ghrelin from hypothalamus

Def of E substrate (eg. hypoG, exercise, fasting), incr aa (eg. Protein meal), glucagon, stress, goint to sleep, L-dopa, apomorphine, oestrogens and androgens (peak at puberty has protein anabolic effect growth; cause incr size of spikes of GH incr release IGF-I growth); thyroid hormones needed for proper release of GH

Decr release: somatostatin (GH release-inhibiting factor; inhibits release of GH, glucagons, insulin, and gastrin); IGF-I (via direct negative feedback on APG and incr relase of somatostatin)

REM sleep, hyperG, cortisol, fa, GH

Effects: stimulate growth (eg. Incr chondrogenesis giganticism if growth plates not fused; if GP’s fused acromegaly – incr size organs, incr protein content, decr fat content); higher spikes during puberty with higher mean plasma level over 24hrs

Works via incr secretion of somatomedins (eg. IGF-I (somatomedin C), IGF-II) synthesized in liver, cartilage and other tissuesIGF-I – secretion independent of GH in utero, but after birth dependent on GH; peaks at puberty then decr thereafterIGF-II – secretion independent of GH; role in growth of fetus; constant level

incr plasma phosporus decr plasma urea nitrogen and aa incr lean body mass decr body fat and chol incr fa (ketogenic, catabolic) incr BMR incr GI absorption of Ca decr renal excretion of Na and K (probably cos redirected to growing tissues) incr GFR and renal blood flow incr hepatic glu output (def causes hypoG) incr ability of B cells to respond to insulinogenic stimuli

FSHMade of α and β subunits which must be combined for max physiologic activity; act via GPCR

LHMade of α and β subunits which must be combined for max physiologic activity; act via GPCR

TSHMade of α and β subunits which must be combined for max physiologic activity

Renal Endocrine Function

Renin-Angiotensin System

Renin: acid aspartyl protease; made as preprorenin converted to prorenin some secreted (very little converted in circulation) some converted to renin in kidneys (in secretory granules of JG cells located in media of afferent arterioles)

HL 80mins

Angiotensinogen: made in liver; incr lvel by GC, thyroid, oestrogens, cytokines, AII

ACE: form AII from AI; inactivates bradykinin (hence cough on ACEi); found in endothelial cells; conversion of AI AII occurs in lungs

Angiotensin: AI (no physiological activity) AII (physiological activity) metabolized rapidly by peptidases (in RBC’s, and many tissues for local effect – uterus, placenta, eyes, pancreas, heart, fat, adrenal cortex, testis, ovary, pituitary, brain) AIII (has 40% pressor activity, 100% aldosterone-stimulating activity) further metabolism to AIV (also has some physiogical activity); also removed from circ by trapping mechanism in vascular beds of various tissues; HL 1-2mins

Mechanism of action of AII:AT1 receptors: serpentine; coupled to Gq PLC incr cytosolic free Ca level; responsible for most effects of AII – found in arterioles and adrenal cortex; XS AII downregulates receptors in arterioles, but upregulates receptors in cortexAT2 receptors: via G protein activate phosphatases antagonize growth effects, open K channels

incr production of NO incr cGMP

Regulation of secretion of renin: Incr release: incr SNS; incr NE+E (act on beta1-receptors on JG cells); PG’s; Na depletion; diuretics; hypotension; haemorrhage; upright posture; dehydration; heart failure; cirrhosis; RAS ( decr afferent arteriole p)Decr release: incr Na and Cl reabsorption across macula densa (renin release inversely proportional to amount of Na and Cl entering DCT from LOH; Na and Cl enter macula densa cells cia Na-K-2Cl transporter); incr afferent arteriolar p; AII (negative feedback); ADHNa-depleted people and cirrhosis circulating AII increased downregulation of receptors in vascular SM decr response

Effects of AII: arteriolar constriction incr SBP and DBP incr aldosterone secretion from adrenal cortex helps release of NE from postganglionic sym neurons contraction of mesangial cells decr GFR incr Na reabsorption in renal tubules decr sensitivity of baroreflex in brain (helps pressor effect) via action on circumventricular organs (area postrema) incr H20 intake via action of circumventricular organs (subfornical organ and organum vasculosum of lamina terminalis) incr secretion of ADH and ACTH via action on circumventricular organs

Erythropoietin

Synthesis: 85% from kidneys (produced by interstitial cells in peritubular capillary bed), 15% from liver (produced by perivenous hepatocytes)Metabolism: metabolized in liver; HL 5hrsMechanism of action: receptor has tyrosine kinase activity inhibits apoptosis of RBC’s and incr growthEffect: Incr no of erthyropoietin-sensitive committed stem cells in BM converted to RBC precursors erthyrocytes; takes 2-3days for incr RBC’sRegulation of release: incr release: hypoxia, androgens, helped by E+NE

GI Physiology

Carbohydrates

Polysaccharides (eg. Starches - glycogen, amylopectin, amylose), disaccharides (eg. Lactose, sucrose), monosaccharides (eg. Fructose, glucose)

DigestionMouth: salivary α-amylase digests starch α-dextrins, maltotriose and maltoseStomach: α-amylase inhibited by acidic gastric juiceSI: salivary and pancreatic α-amylase active as above Oligosaccharidases present in brush border \ α-dextrinase – breaks down α-dextrins, maltotriose and maltose

Maltase – breaks down α-dextrins, maltotriose and maltoseSucrase – breaks down sucrose, maltotriose and maltose

Disaccharidases present in BB Lactase – breaks down lactoseTrehalase – breaks down trehalose

Sucrase 1 glu + 1 fru Lactose glu and galactose Trehalose 2 glu

Def in enzymes osmotic diarrhoea, bloating + flatulence (due to production of CO2 and H2 from disaccharies in lower SI and LI)Def lactase lactose intolerance

AbsorptionGlucose: rapid absorption in all SI (no absorption in LI) – via Na-dependent glu transporter (SGLUT) a Na-glu cotransporter (incr absorption if incr Na conc on mucosal surface of cells); same mechanism for galactose

1) Na moves along conc gradient2) Na undergoes AT into lateral intercellular spaces (maintaining conc grad)3) Glu transported by GLUT2 into interstitum and capillaries

Fructose: facilitated diffusion by GLUT5 in enterocytes, then via GLUT2 into intersitium; independent of Na

Pentoses: simple diffusion

Proteins

Digestion

Endopeptidases (eg. Trypsin, chymotrypsin, elastase) - digest interior peptide bondsExopeptidases (eg. Carboxypeptidase A and B) - digest aa at carboxyl ends

Stomach: pepsinogen I (in acid secreting regions) and pepsinogen II (in pyloric region) activated by HCl pepsin digest proteins and polypeptides (cleave peptide linkages)

Work in acidic enviro so decr activity when gastric contents mixed with alkaline pancreatic juice in duodenum and jejunum

SI: occurs in 3 sites1) Enzymes from pancreas – act in lumenEnteropeptidase stimulates trypsin (endo) digests proteins and polypeptides Trypsin stimulates Chymotrypsin (endo) digests proteins and polypeptides

Elastase (endo) digests elastin and other protesin Carboxypeptidase A and B (exo) digest proteins and polypeptides

Nucleases digest nucleic acids nucleotides

2) Enzymes from SI mucosa – act in brush borderEnteropeptidase: digests trypsinogen trypsinAminopeptidase digests polypeptides

Carboxypeptidase digests polypeptidesEndopeptidases digests polypeptidesDipeptidase digests dipeptides 2aaEnzymes split nucleotides nucleosides and phosphoric acid sugars and purine and pyrimidine bases

3) Intracellular mucosal enzymes:Peptidases digest di- and tripeptides which are AT into intestinal cells

AbsorptionRapid in duodenum and jejunum, slow in ileum, none in LI; 50% from food, 25% from digestive juices, 25% from desquamated cellsMultiple systems – into enterocytes: 3 systems require Na, 2 require Na and Cl, 2 don’t need Na Into blood: 3 system require Na, 2 don’t need Na

2-5% not absorbed digested by bacteria in LI excretedProtein absorption indicated in food allergies; absorption of protein Ag’s occurs in microfold cells overlying Peyer’s patches Ag presented to lymphoid cells

Lipids

DigestionMouth: lingual lipase from Ebner’s glands on dorsal surface of tongue digests up to 30% triG’s fa + 1,2-diacylglycerols; still active in stomach

SI: most occurs in duodenum; emulsified by bile salts, lecithin and monoglycerides form micelles which contain fa, monoglycerides and chol in hydrophobic centres these can pass to BB for digestionPancreatic lipase digests triG’s 2 monoglycerides and fa; action inhibited by acid, but OK as pancreatic juice is alkaline

Colipase binds to pancreatic lipase, increasing action; released in prohormone form which is activated by trypsin

Bile salt-acid lipase (lipase activated by bile salt) digests cholesteryl esters chol; also digests esters of fat-soluble vitamins and phospholipidsCholesteryl ester hydrolase digests cholesteryl esters chol

Absorption – mostly in upper SI; 95% absorbedPassive diffusion / carriers into enterocytes rapidly esterified in enterocytes so conc grad maintained

small fa’s are H20-soluble so can be ATed into blood and circulate as free fa’s larger fa’s are reeesterfied to triG in SER chol is esterified

esters coated in protein, cholesterol and phospholipid chylomicron enter lymphatics via exocytosis

NB. Colonic bacteria short-chain fa’s via action on carbs and fibre absorbed and metabolized, have trophic effect on colonic epithelial cells, combat inflamm, help maintain acid-base equilibrium, promote absorption of Na

H20 and Electrolytes

2000ml ingested + 7000ml secreted 98% reabsorbed, 200ml lost in stools

Na: Na moves either way depending on conc grad Na-K ATPase in BL membrane some Na active absorbed in SI and esp in LI 2Y AT of Na with glu and aaCl: from IF enterocyte via N-K-2Cl cotransporter Cl secreted into lumen via channels (activated by incr cAMP)H20: move according to osmotic p – usually equals out at the jejunum then maintained thereafter; much absorption in LI 2Y to AT of Na

K: some secreted into lumen (eg. As part of mucus) and some passively enters lumen down conc grad H-K-ATPase in distal LI causes AT of K into enterocytes

Vitamins and Minerals

Vitamins: ADEK fat soluble; mostly in upper SI; B12 in ileum (bound to intrinsic factor from stomach); B12 and folate Na-independent, but others co-transported with NaCa: 30-80% absorbed; incr absorption is defiency, decr if XSFe: Fe3+ ingested Fe3+ reductase in BB converts to Fe2+ (aided by gastric secretions which dissolve Fe3+ making reduction easier) Fe2+ absorbed in duodenum via DMT1

stored as ferritin in enterocytes; may aggregate as haemosiderin transported into IF via ferroportin 1 (facilitated by hephaestin)

Fe2+ converted back to Fe3+ in plasma bound to transport protein transferrin (has 2 binding sites; usually 35% saturated)

70% Fe in Hb, 3% in myoglobin, 27% in ferritin; XS Fe accum of haemosiderin which causes damaged haemachromatosis

Regulation of GI function

Layers:1) Muscosa2) Submucosa: contains SM fibres (circular)3) Muscularis: contains 2 layers of SM (inner circular, outer longitudinal)4) Serosa: continues on to mesentery

Nervous Supply:1) Myenteric (Auerbach’s) plexus: between 2 muscle layers in muscularis; innervates these muscles,

involved in motor control2) Submucous (Meissner’s) plexus: between mucosa and submucosa; innervates glands, endocrine

cells and BV’sPNS: preganglionic paraS efferents end on cholinergic nerve cells in plexuses incr Ach secretionSNS: postganglionic sym efferents end on cholinergic nerve cells in plexuses NE inhibits Ach secretion via alpha-2 receptors; some end directly on SM cells or on BV’sBasic electrical activity: (not in oesophagus and prox stomach) SM has spontaneous rhythmic fluctuations in membrane potential (-65 - -45mV); initiated by interstitial cells of Cajal located near myenteric plexus in stomach and SI, near submucous plexus in colon; rarely causes contraction but cause muscle tension; depolarization due to Ca influx, repolarisation due to K efflux; Ach incr tension, E decr; co-ordinates motor activity – contraction only occurs during depolarizing part of waveMigrating motor complex: quiescent period (I) irregular electrical and mechanical activity (II) bursts of regular activity (III); occur every 90mins with cycles migrating from stomach to distal ileum; stopped by ingestion of food, only during fasting statePeristalsis: reflex response inititated when wall stretched release of 5-HT activates sensory neurons activates myenteric plexus release of substance P and Ach SM contraction behind bolus release of NO, VIP and ATP SM relaxation ahead of bolusMoves at 2-25cm/sec; occurs intrinsically, but influenced by extrinsic input

GI hormones: Enteroendocrine cells: are hormone secreting; called enterochromaffin cells if also secreted 5-HT; called APUD/neuroendocrine cells if also secrete amines

Gastrin: Synthesis: Preprogastrin processed into multiple gastrins of multiple lengths (G17 is principle form causing gastrin secretion); produced by G cells antral portion of gastric mucosa; contain many gastrin granules; some gastrin also found in pancreas, APG, IPG, hypothalamus, medulla, vagus and sciatic nerves

Regulation of secretion: G cells have microvilli at luminal border detect changes in gastric contentsIncr secretion: luminal peptides and aa; luminal distension; incr vagal discharge (release gastrin-releasing polypeptide (GRP) at G cells); Ca and E in bloodDecr secretion: luminal acid and somatostatin; secretin, GIP, VIP, glucagons and caltinonin in blood

Metabolism: HL 2-3mins for principle form; inactivated in kidney and SIEffects: stimulation of gastric acid and pepsin secretion

trophic action of mucosa of SI, LI and stomachstimulates gastric motilitystimulates insulin secretion (after protein meal)incr glucagons secretion

Cholecystokinin-Pancreozymin (CCK-PZ / CCK)Sythesis: secreted by I cells in mucosa of upper SI, nerves in distal SI and LI (also found in brain); preproCCK processed into many fragments; CCK 8 and 12 are most activeMetabolism: 5mins

Regulation of secretion:Incr secretion: contact of intestinal mucosa with products of digestion (peptides and aa and fa); digestion caused by release of pancreatic juice causes +ve feedback loopDecr secretion:

Mechanism of action: CCK receptors activate PLC incr production IP3 and DAGEffects: contraction of GB

Secretion of pancreatic juiceHelps action of secretin in causing secretion of pancreatic juiceInhibits gastric emptying (augments contraction of pyloric sphincter)Trophic effect on pancreasIncr secretion of enterokinaseIncr motility of SI and LIIncr glucagon secretionStimulates insulin secretion

SecretinSynthesis: secreted by S cells in mucosa of upper SIMetabolism: HL 5mins

Regulation of secretion:Incr secretion: products of protein digestion; acidic contents of SIDecr secretion:

Mechanism of action: works via cAMPEffects: incr secretion of HCO3 by duct cells of pancrease and biliary tract secretion of waterly,

alkaline pancreas juiceaugments actions of CCK in causing secretion of pancreatic juicedecr gastric acid secretioncontraction of pyloric sphincterstimulates insulin secretion

GIPSynthesis: made by K cells in muscosa of duodenum and jejunumRegulation of secretion: inc by glu and fat in duodenumEffects: inhibits gastric secretion and motility in high doses; stimulates insulin secretion

VIP

Synthesis: preproVIPMetabolism: HL 2minsEffects: stimulates intestinal secretion of electrolytes and H20; relaxation of intestinal SM; dilation of peri BV’s; inhibition of gastric acid secretion; potentiates action of Ach at salivary glands

Peptide YYInhibits gastric acid secretion and motility; release from jejunum stimulated by fat

GhrelinSecreted in stomach; stimulates GH secretion; central control of food intake

MotiliinSecreted by enterochromaffin cells and Mo cells in stomach, SI and colon; acts on GPCR’s in duodenum and colon contraction of SM in stomach, SI and LI; regulator of MIC’s

SomatostatinSecreted by D cells in pancreatic islets and GI mucosa; inhibits secretion of gastrin, VIP, GIP, secretin and motilin, pancreatic exocrine secretion, gastric acid secretion, gastric motility, GB contraction, absorption of glu, aa and triG’s; stimulates acid in lumen

Neurotensin: from mucosa of ileum; stimulate by fa; inhibits GI motility and incr ileal blood flowSubstance P: incr motilityGRP: in vagal nerve ending terminating on G cells; incr gastric secretionGuanylin: from intestinal mucosa; incr conc of intracellular cGMP incr secretion of Cl into lumen

MouthMastication: wet, smaller particles

Saliva: 1500ml/day; helps swallowing, keeps moist, solvent for molecules, neutralize gastric acid when regurgitated into oesophagus; hypotonic, slightly acidic, rich in K, low in Na and Cl (when salivary flow rapid, less time for removal of Na and Cl and addition of K and HCO3 in ducts saliva more isotonic)

Glands: Parotid: serous, watery; 20%Submandibular: mixed, moderately viscous; 70%Sublingual: mucous, viscous; 5%

Salivary glands contain zymogen granules containing salivary enzymes discharged from acinar cells into ducts; contains:

Lingual lipase: by glands on tongueα-amylase: by salivary glandsMucins: glycoproteins that lubricate food, bind bacteria, protect oral mucosaImmune globulin IgA\Lysozyme: attacks walls of bacteriaLactoferrin: binds Fe, bacteriostaticProline-rich proteins: protect tooth enamel, bind toxic tannins

Regulation of secretion: PNS incr secretion of watery saliva, vasoD in gland due to VIP Atropine and anticholingergics decr saliva SNS vasoC in gland, decr saliva

Swallowing: afferent impulse: trigeminal, GP and vagus nerves nucleus of tractus solitarius and nucleus ambiguous

efferent impulse: trigeminal, facial and hypoglossal nervesVoluntary stage: tongue pushes backwardsInvoluntary stage: contraction of pharyngeal muscles, inhibition of resp and glottic closure, peristalsis at 4cm/sec

OesophagusLower oesophageal sphincter: tonically active (prevents reflux) but relaxes on swallowing; vagal input causes contraction; release of NO and VIP from interneurons causes relaxation; achalasia due to incr tone due to deficiency of myenteric plexus decr release NO and VIP

1) Intrinsic sphincter: more prominent SM2) Extrinsic sphincter: fibres of diaphragm surrounding oesophagus3) Oblique fibres of stomach wall create flap valve that helps prevent regurg when intraG p rises

StomachSecrete gastric juice (2500ml)

Cardia and pyloric region: neck cells of gastric glands and mucosa secrete mucus (with HCO3, made of glycoproteins called mucins) alkaline pH at luminal surface; incr by PGBody: several glands open onto gastric pitContains parietal (oxyntic) cells: secrete HCl and IF

HCl: kills bacteria, necessary pH for digestion, stimulates flow of bile stimulated by histamine via H2 ( incr cAMP via Gs), Ach via M3 ( incr intracellular Ca), gastrin (incr intracellular Ca)) and IF Inhibited by PG but activating Gi H-K ATPase pumps H (from CO2 + H20 H2CO3 (catalysed by CA) H + HCO3) against conc grad and IF; at rest cell contains tubulovesicular structures in walls on

activation, structures move to apical membrane inserting more H-K ATPase into it Cl channels activated by cAMP transport Cl down electrochemical grad into lumen; Cl \ enters parietal cell from blood via countertransport with HCO3 from above (after meal, may get postprandial alkaline tide as blood becomes alkaline) IF: binds to cyanocobalamin (B12) complex taken up by cubilin in receptors in distal ileum absorption of complex by endocytosis B12 transferred to transcobalamin II which transports B12 in plasmaChief (zymogen / peptic) cells: contain zymogen granules secrete pepsinogensEnterochromaffin-like (ECL) cells: secrete histamine; stimulated by gastrin; inhibited by Somtostatin

Dumping syndrome: in gastrectomised pt; rapidly absorption of glu incr insulin hypoG weakness, dizziness, sweating; hypertonic meals rapidly entering intestine movement of H20 into gut hypoV

Gastric MotilityMechanism: food enters stomach upper part relaxes (receptive relaxation; vagal; triggered by mvmt of oesophagus) peristalsis in lower, mixing (contraction in distal part is antral systole; 3-4 waves/min) contraction of pyloric region and duodenum; liquid food enters duodenum (pyloric contraction prevents regurg due to CCK and secretinRegulation: cephalic (CNS; presence of food in mouth incr vagus output incr gastrin via GRP, incr Ach

to incr acid and pepsin; incr by anger, decr by fear and depression) gastric (local reflex responses to gastrin; stretch and chemical stimuli esp aa; receptors submucosal plexus synapsing on postganglionic paraS neurons parietal cells gastrin) intestinal (reflex and hormonal feedback; fats, carbs and acid in duodenum inhibit gastric aicd and pepsin secretion and gastric motility via peptide YY)alcohol and caffeine act directly on mucosaOsmolarity of contents: duodenal osmoreceptors sense hyperosmolarity decr gastric emptying

Empting fastest for carbs > protein > fat

PancreasZymogen granules contain digestive enzymes exocytosis into lumens of pancreatic ducts pancreatic duct of Wirsung joins CBD ampulla of Vater opening in duodenal papilla, encircled by sphincter of Oddi

Pancreatic juice: 1500ml/day

high HC03 neutralize gastric acidalso contain Na, K, Ca, Mg, Cl, SO4, HPO4enzymes – secreted as proenzymes Trypsinogen converted to trypsin by enteropeptidase (from BB; NOT activated in pancreas as this would cause autodigestion), also activated by trypsin itself (+ive feedback loop; pancreas contains a trypsin inhibitor) Trypsin: converts chymotrypsinogens chymotrypsin Proenzymes active enzymes

Regulation of secretion: secretin acts on ducts juice rich in alkaline (high HCO3, low Cl), low in enzymes (due to incr cAMP)

incr bile secretion CCK acts on acinar cells juice high in enzymes, low in volume (via PLC)

Ach acts on acinar cells jucie high in enzymes, low in volume (via PLC)

Liver and Biliary SystemBlood extensively modified on passage through liver (portal vein sinusoids central veins hepatic veins IVC) – acini, at one side portal vein, hepatic artery, bile duct, this area has best oxygenationBile formation: intralobular BD interlobular BD R+L hepatic ducts CHD unites with CD CBDFunctions: formation and secretion of bile

Metabolism of glu, aa, lipids, fat and water soluble vits Inactivation of toxins, steroids and other hormones

Synthesis of acute phase proteins, albumin, CF’s, steroid and hormone-binding proteins Kuppfer cells for immunity

Bile: Alkaline; 500ml/dayMade of bile salts (Na and K salts of bile acids; conjugated to glycine and taurine; made from chol)

Cholic and chenodeoxycholic acid formed in liver2Y bile acids: Cholic deoxycholic acid by bacteria in LI

Chenodeoxycholic lithocholic acid by bacteria in LIReduce surface tension; emulsification of fat (amphipathic so can form micelles – hydrophilic out, hydrophobic in)90-95% absorbed from SI via Na-bile salt cotransporter powered by basolateral Na-K ATPase portal vein reexcreted in bile5-10% enter colon converted as above lithocholic acid excreted, deoxycholic acid absorbed and H20 soluble

bile pigments (glucuronides are bilirubin and bilverdin – breakdown products of heme)Bilirubin: formed by breakdown of Hb bound to albumin enters liver cells

bound to cytoplasmic proteins conjugated to glucuronic acid by glucuronyl transferase (activity incr by barbs, antihistamines, anticonvulsants) in SER bilirubin diglucuronide (more H20 soluble)

AT into bile canaliculi SI which is impermeable to conjugated bilirubin, most of which excreted but colon bacteria can form urobilinogen which can be reabsorbed into general circ or enterohepatic circ excreted in urine small (conjugated) amount enters blood excreted in urine

Jaundice can be due to XS production of bilirubun, decr uptake of bilirubin into hepatic cells, disturbed intracellular protein binding/conjugation incr

free bilirubin disturbed secretion of conjugated bilirubin, intr/extrahepatic bile duct obstruction incr conjugated bilirubin

If bile doesn’t enter faeces white acholic stoolsAlso secreted in bile: chol (supersaturation gallstones; not able to form micelles if too much),

ALP

Gallbladder: absorption of water in stored bileCholagogues: cause contraction of GB; CCK

Choleretics: cause incr secretion of bile; vagus nerve, secretin

Small Intestine

Duodenum becomes jejunum at ligament of Treitz upper 40% jejunum, lower 60% ileum ends at ileocaecal valveContains solitary lymphatic nodules

aggregated lymphatic nodules (Peyer’s patches) intestinal glands (crypts of Lueberkuhn) throughout - enterocytes formed from undifferentiated cells here which migrate to tips of villi; ave lifespan 2-5/7 as rapidly sloughed; secrete isotonic fluid; contain Paneth cells in bottom which secrete defensins – natural AB’sduodenal (Brunner’s glands) – secrete mucusvarious enteroendocrine cellsvalvulae conniventesm membrane covered in villi covered by single layer of columnar epithelium containing network of capillaries and lymphatic vessel (lacteal), with submucosa running to tip of villus; free edges of cells in villi form microvilli covered in glycocalyx (layer rich in amino sugars) which make up brush borderepithelial cells – secrete mucusgoblet cells – secrete mucus in SI and LI

Cells connected by tight junctionsMucus secretion incr by cholinergic stimulation, chemical and physical irritation

Motility: MMCs present; replaced by peristalsis controlled by BER; 12 BER cycles/min in prox jejunum 8 in distal ileum; Peristaltic rushes are intense waves occurring when obstruction present; mvmt below slow transit time

Segmental contractions move chime to and fro, incr exposure to mucosal surface, initiated by focal incr Ca influxTonic contractions prolonged contractions which separate regions of SI from eachother

Intestinal adaption: when some bowel removed, hyperplasia and hypertrophy of remaining bowel; still malabsorption if >50% bowel removed (decr enterohepatic circ decr fa absorption, osmotic effect of unabsorbed bile salts enter colon where incr intestinal secretion; jejunum worse at adapting so worse if distal ileum removedParalytic ileus: due to activation of opioid receptors / incr discharge from NA fibres in splanchnic nerves; lasts 6-8hrs in intestine, 2-3/7 in colon

Colon 4hrs to get to cecum, 6 hrs to hepatic flexure, 9hrs to splenic flexure, 12hr to pelvisFor absorption of H20, Na and minerals; external muscle layer collected into 3 longitudinal bands (teniae coli) haustra; no villi; short glands; solitary lymph follicles; ileum progects into cecum so incr colonic p closes ileocaecal valve, but incr ileal p opens it; gastroileal reflex causes relaxation of cecum, SNS causes contraction of valveNa AT out, H20 along osmotic grad; net secretion of HCO3 and KSegmentation contraction and peristalsis in colon, also mass action contraction with large contraction of SM move material defecation reflex; BER 2/min at ileocaecal valve, 6/min at sigmoid

Intestinal bacteria: eg. E coli, enterobacter aerogenes, bacteroides fragilis; may use nutrients (eg. Aa’s), but also make nutrients (eg. Folic acid, B vits, vit K, fas); role in cholesterol metabolism; 3 types:

1) Pathogens : cause disease2) Symbionts : benefit host3) Commensals : no effect on host or vice versa

Dietary fibre: cellulose, hemicellulose, lignin, gums, algal polysaccharides, pectic substances; poorly digested; forms bulk

Defecation: a spinal reflex that can be inhibited or facilitated voluntarily

SNS to internal anal sphincter contraction (involuntary); relaxes on distension with reflex muscular contractions external anal sphincter nerve supply from pudendal nerve; tonic contraction relaxes when p 55mmHg in rectum / voluntary defecation due to straining (abdo muscles contract, pelvic floor lower 1-3cm, relaxation of puborectalis, decr anorectal angle to 15 deg

Gastrocolic reflex: distension of stomach contractions in rectum

BLOOD

Plasma Composition

Circulating Body Fluids

Blood: normal circulating vol is 8% body weight, 5600mL; 55% of vol is plasmaBone marrow: extramedullary haematopoiesis occurs BM disease; in children occurs in all bones, by 20yrs only in long bones; active cellular marrow is red marrow, inactive is infiltrated with fat yellow marrow; 75% is WBC, 25% is RBC as average life span of WBC is short; HSC’s best derived from blasocytes of embryos in umbilical cord blood

Granuloctye and Macrophage Colony-Stimulating Factors: stimulate growth of certain cell lines; also sustain mature cells; some crossing-over of action of factors; usually acting locally in BM; Stem cell factor – needed from prolif and maturation of HSC’s

Cytokine Source Cell Line StimulatedIL-1 Multiple cell types Erythrocyte, granulocyte, megakaryocyte, monocyteIL-3 T cells Erythrocyte, granulocyte, megakaryocyte, monocyteIL-4 T cells BasophilIL-5 T cells EosinophilIL-6 Endothelial cells, fibroblasts, macrophages Erythrocyte, granulocyte, megakaryocyte, monocyte

IL-11 Fibroblasts, osteoblasts Erythrocyte, granulocyte, megakaryocyteErythropoietin Kidney, Kupffer cells ErythrocyteSCF Multiple cell types Erythrocyte, granulocyte, megakaryocyte, monocyteG-CSF (granulocyte) Endothelial cells, fibroblasts, monocytes GranulocyteGM-CSF (granulocyte-macrophage) Endothelial cells, fibroblasts, monocytes, T cells Erythrocyte, granulocyte, megakaryocyteM-CSF (macrophage) Endothelial cells, fibroblasts, monocytes MonocyteThrombopoietin Liver, kidney Megakaryocyte

WBC’s: 4000-11000cells/ μLGranulocytes/polymorphonuclear leukocytes: horseshoe nuclei, become lobed as older; contain cytoplasmic granules that contain substances involved in inflamm/allergic reactions

Neutrophils: 3000-6000cells/μL; 50-70% of WBC; halflife 6hrs; attracted to endothelial cell surfaces by selectins roll along it bind to neutrophil adhesion molecules of integrin family pass through wall of capillaries between endothelial cells by diapedesisEosinophils: 150-300cells/ μL; 1-4% of WBC; halflife short; also undergo diapedesis; maturation and activation induced by IL3 and 5, GM-CSFBasophils: 0-100cells/ μL; 0.4% of WBC

Lymphocytes: large round nuclei and scanty cytoplasm; 1500-4000cells/ μL; 20-40% of WBCMonocytes: much agranular cytoplasm and kidney-shaped nucleus; 300-600cells/ μL; 2-8% of WBC

Mast cells: heavily granulated wandering cells found in areas rich in CT; contain heparin, histamine and proteases; have IgE receptors and degranulate when IgE coated antigens bind them

Monocytes: circulate for 72hrs then enter tissues and become tissue macrophages (eg. Kupffer cells in liver, pul alveolar macrophages, microglia in brain) where they persist for 3/12

Lymphocytes: enter blood stream via lymphatics; only 2% usually found in blood, rest in lymphoid organsLymphocyte precursors come from BM

thymus to be transformed into T cells to LN’s to bodyT cells cytotoxic (CD8) – destroy foreign cells; development aided by helper T cells; divided into αβ and γδ types

helper 1 (CD4) – secrete IL-2 and γIF, important in cellular immunity helper 2 (CD4) – secrete IL-4 and 5, interact with B cells for humoral

immunity memory T cells bursal equivalents (eg. fetal liver, BM, spleen) to be transformed into B cells to LN’s to

bodyB cells plasma cells – secrete Ig from Ag-binding receptors

memory B cells

Antibodies: 1) Bind and neutralize protein toxins2) Block attachment of viruses and bacteria to cells3) Osponise bacteria4) Activate complement

Natural Killer Cells: are cytotoxic lymphocytes, but are not T cells

Cytokines: hormone-like molecules that act in paracrine fashion to regulate immune responses; a superfamily are chemokines which attract WBC’s to areas (receptors are G proteins)

Cytokine Source Activity RelevanceIL-1 Macrophages Activate T cells and macrophages; causes fever; Septic shock, RA, atherosclerosis

incr slow wave sleep and decr appetiteIL-2 TH1 cells Activate lymphocytes, NKC’s and macrophages Trt of metastatic RCC, melanoma, tumoursIL-4 TH2 cells, mast cells,

basophils, eosinophilsActivate lymphocytes (esp TH2), monocytes, IgE class switching

Allergy

IL-5 TH2 cells, mast cells, eosinophils

Differentiation of eosinophils Allergy

IL-6 TH2 cells, macrophages Activation of lymphocytes, differentiation of B cells, stimulate production of acute-phase proteins; causes fever

Acts as GF in myeloma

IL-8 T cells and macrophages Chemotaxis of neutrophils, basophils, T cells Marker of disease activityIL-11 BM stromal cells Simulate production of acute-phase proteins Decr chemotherapy-induced

thrombocytopaeniaIL-12 Macrophages and B cells Stimulate production of IFγ by TH1 cells and

NKC’s; induce TH1 cellsVaccines

TNFα Macrophages, NKC’s, T and B cells, mast cells

Inflammation; causes fever RA

Lymphotoxin (TNFβ)

TH1 cells and B cells Inflammation MS and IDDM

TGFβ T cells, B cells, mast cells and macrophages

Immunosuppression MS and MG

GM-CSF T cells, B cells, NKC’s and macrophages

Promote growth of granulocytes and monocytes Decr neutropenia after chemo; stimulate cell production after BM transplant

IFα Virally infected cells Induce resistence of cells to viral infection AIDS, melanoma, chronic hepatitis B and CIFβ Virally infected cells Induce resistence of cells to viral infection Decr relapse of MSIFγ TH1 cells and NKCs Activate macrophages, inhibit TH2 cells Help chronic granulomatous disease

Complement system: 3 pathways activate system1) Classic pathway: triggered by immune complexes2) Mannose-binding lectin pathway: triggered when lectin binds mannose groups in bacteria3) Alternative/properdin pathway: triggered by contact with pathogen

Pathways work in various manners;1) Opsonisation chemotaxis lysis by inserting perforins into cell membranes disrupt membrane polarity2) Activate B cells and aid immune memory3) Dispose of waste products after apoptosis

Inflamm response: may kill bacteria / damage host tissue (eg. RA)1) Incr production of neutrophils

a. Bacteria interacts with factors and cells to cause chemotaxis of neutrophils to infected area via chemokines (C5a, leukotrienes, mast cells, basophils); this movement + phagocytosis require microfilaments and microtubules, interaction of actin and myosin-I

b. Plasma factors cause opsonisation of bacteria – usually IgG and complement proteins added so can bind easily to neutrophil G-protein mediated response incr motor activity of cell ingestion of bacteria by phagocytosisexocytosis (neutrophil granules discharge contents into phagocytic vacuoles, and into interstitial space – degranulation) Granules contain defensins (antimicrobial proteins) proteases elastases metalloproteinases (attack collagen)

c. Respiratory burst: cell membrane enzyme NADPH oxidase activated toxic oxygen metabolites to help kill; this requires incr O2 uptake and metabolism of neutrophilNADPH + H+ + 2O2 NADP + 2H+ + 2O2- (free radical)O2- + O2- + H+ + H+ H2O2 + O2 (catalysed by superoxide dismutase) (both are bactericidal)H2O2 H2O + O2 (catalysed by catalase)

d. Myeloperoxidase: released by neutrophils, catalyses conversion of Cl, Br, I, and SCN to acids (HOCl, HOBr etc…) which are oxidants

2) Incr activity of eosinophilsa. Release proteins, cytokines and chemokines that produce inflammation; esp abundant in

GI, RS and GU tract mucosa; incr in allergic disorders and other RS/GI diseases; more selective than neutrophils

3) Incr activity of basophilsa. Release proteins and cytokines; contain histamine and heparin which are all released

when activated by histamine-releasing factor secreted by T cells; for immediate hypersensitivity

4) Incr activity of mast cellsa. Involved in inflamm reactions initiated by IgE and IgG; release TNF-α by ab-

independent mechanism non-specific natural immunity; involved in allergic reactions5) Incr activity of macrophages

a. Activated by lymphokines from T cells migrate via chemotaxis phagocytosis similar to neutrophils; secrete substances that affect lymphocytes, PGE and CF’s

Phagocytic disorders: Neutrophil hypomotility: poorly polymerized actin slow neutrophilsChronic granulomatous disease: failure to make O2 in neutrophils and monocytesG6PD def: failure to make NADPH and hence decr O2 production

Immunity:Innate immunity: found in invertebrates and 1st line defense in vertebratesReceptors bind sequences of sugars/fats/aa found in common bacteria / urate crystals secreted by bacteria activate immune response defense mechanisms via NKC’s, neutrophils, macrophages

release of IF’s, phagocytosis, antibacterial peptides, complement system, proteolysis activate acquired immune system

Eg. TLR4 (toll receptor) binds bacterial lipopolysaccharide protein CD14 (important in production of septic shock in G-ive bacteria) cascade of immune eventsEg. TLR2 for microbial lipoproteins, TLR6 for peptidoglycans, TLR9 for DNA

Acquired immunity: specific Ag’s activate T and B cells production of ab’s1) Humoral immunity: mediated by ab’s (in γ globulin fraction of plasma proteins) produced by B

cells activate complement system and neutralize ag’s; important in bacterial infection2) Cellular immunity: mediated by T cells insert perforins; important in viral/fungal infections,

delayed allergy, rejection of transplants, fighting tumours

Antigens: Ag taken up by APC – can be dendritic cells in LN’s, spleen and skin macrophages B cellsAg partially digested in APC peptide fragment coupled to HLA (human leukocyte Ag’s) - protein products of MHC (major histocompatibility complex) genes on C6

Class I – heavy chain assoc noncovalently with β2-microglobulin; found on all nucleated cells; mainly coupled to peptide fragments generated from proteins (in proteasomes)

from WITHIN cellsClass II – lighter chain assoc noncovalently with lighter β chain; present in APC’s (inc B cells and

activated T cells); mainly couped to peptide fragments from EXTRACELLULAR proteins that enter cell by endocytosis (eg. bacteria)

HLA-Ag complex put on cell surface presented to αβ T cell receptors (made up of α and β units) Cytotoxic (CD8) T cells bind MHC-I kill target directlyHelper (CD4) T cells bind MHC-II T cells secretes cytokines that activate other lymphocytes

For T cell activation 2 signals needed - there is also binding of adhesion molecules to complementary proteins in APC

B cells can binds Ag’s directly contact TH2 cell for activation and ab formation memory B and plasma cells (secrete ab’s)

ImmunoglobulinsBind and neutralize protein toxins; block attachment of viruses and bacteria to cells; opsonise bacteria; activate complementMade of 4 polypeptide chains – 2 heavy chains, 2 light chains – joined by disulphide bridges that permit mobility; heavy chains flexible at hinge; contain C constant segment, and variable segments (J joining, D diversity, V variable); V are Ag binding sites; Fc portion is effector portion

IgG: complement activationIgA: localized protection in external secretions (secretory immunoglobulins)IgM: complement activationIgD: Ag recognition by B cellsIgE: reagin activity; releases histamine from basophils and mast cells

Platelets: Small granulated bodies that accumulate at sites of vascular injury; no nuclei; HL 4/7; formed from megakaryocytes in BM by pinching off bits of cytoplasm; 60-75% in blood, rest in spleen; membranes have receptors for collagen, ADP, vWF and fibrinogenCytoplasm contains dense granules (containing substances secreted on plt activations – 5-HT, ADP,

adenine nucleotides) α-granules (contains proteins in lysosome – CF’s, PDGF (stimulates wound healing,

mitogen for vascular SM))Production regulated by CSF’s from megakaryocytes and thrombopoietin (from liver and kidneys)BV wall injury exposed collagen and von Willebrand factor in wall plts adhere via receptors plt activation release contents of granules

ADP stimulates more plt aggregation (aided by platelet activating factor from neutrophils and monocytes which acts via GPCR incr arachidonic acid derivatives (eg. TXA2))

Red Blood Cells:Biconcave discs made in BM; no nuclei; last 120days; shrink/swell depending on osmotic p (haemolyse in hypotonic saline); spleen removes abnormal RBC’sHb: O2 carrying pigment; globular molecule made of 4 subunits each containing heme (Fe containing porphyrin derivative) and polypeptides (2 pairs per Hb molecule) which form globin portion; binds O2 oxyHb (O2 attaches to Fe in heme; H and 2,3BPG compete with O2 decr affinity of Hb for O2); drugs may cause Fe2+ to be converted to Fe3+ methemoglobin; CO reacts with Hb COHb (has much higher affinity for Hb than O2)

HbA: α2β2; normal adult HbHbA2 (2.5%): α2δ2HbF: α2γ2; bind less avidly to 2,3-BPG so higher affinity for O2Gower 1 Hb: ζ2ε2 (in embryo)Gower 2 Hb: α2ε2 (in embryo)

Catabolism: RBC’s destroyed in tissue macrophage system heme converted to bilverdin (CO formed in process) converted to bilirubin and excreted in bile

Plasma:Normal plasma vol is 5% body weight (3500ml); contains CF’sIf whole blood allowed to clot, and clot removed remaining is serum (same as plasma but minus fibrinogen, CF II, V, VIII)Plasma proteins: albumin, globulin, fibrinogen, CF’s, ab’s; capillary walls impermeable to these exert 25mmHg oncotic pressure across capillary wall pulling H20 into blood; also responsible for 15% buffering capacity of blood; mostly anionic; most made in liver except ab’sLow in liver disease, starvation, malabsorption

Lymph:

Tissue fluid that enter lymphatic vessels enters venous blood via thoracic and R lymphatic ducts; contains CF’s; lower protein content than plasma; involved in absorption of H20-insoluble fats; lymphocytes enter blood through lymph

Haemostasis:Damage to blood vessel wall constriction (due to 5-HT) and formation of haemostatic plug of plts as they bind to collagen and aggregate bound together by insoluble fibrin as fibrin monomer polymerises and has covalent cross-linkages, catalysed by XIII and requiring Ca (formed from soluble fibrinogen in clotting cascade) definitive clotThrombin: activates plts, endothelial cells, leukocytesSEE DIAGRAMS

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