11 Animal Physiology - Excretory Systems

Principles of Animal PhysiologyExcretory SystemExcretory System

▪ Primary functions:Introduction

▪ Primary functions:▸ Maintenance of proper internal levels of inorganic solutes (Na+ K+ Cl CO2 etc)solutes (Na+, K+, Cl-, CO2, etc)▸ Maintenance of proper plasma water volume▸ Removal of nonnutritive and harmful substances from metabolism (ammonia, urea, bilirubin, etc)▸ Maintenance of osmotic balance

▪ Organ systems involved in excretion and retentionIntroduction

g y▪ Respiratory system▸ Regulate O2 and CO2▸ Gills can remove ammonia and HCO3-Gills can remove ammonia and HCO3▸ Participate in acid-base balance

▪ Digestive system▸ R l f di t d f d d t▸ Removal of undigested food and wastes▸ May regulate ion and water

▪ Integumentory system▸ Can excrete organic wastes▸ May regulate salt and water uptake

▪ Renal organsg▸ Filter body fluids▸ Regulate water, ions and organic substances

▪ Nitrogenous products from nitrogen metabolismIntroduction

Nitrogenous products from nitrogen metabolism▸ Ammonia (NH3)♦ Most bony fishes, larval amphibians and most invertebratesy , p

♦ They are called ammonotelic animals

▸ Urea♦ Most adult amphibians and mammals

♦ They are called ureotelic animals

▸ Uric acid▸ Uric acid♦ Insects, birds, most reptiles, tree frogs and desert toads

♦ They are called uricotelic animals

▪ Excretion of nitrogenous wastesIntroduction

▪ Renal organs modify body fluids by four basic renal processes:▸ Filtration♦ Movement through a semipermeable membrane

♦ An ultrafiltration is produced

▸ Secretion▸ Secretion♦ Specific solutes are transported into the tubule lumen for excretion

▸ Reabsorptionp♦ Specific solutes are transported back into the body from the lumen

▸ Osmoconcentration♦ Water is removed from the lumen leaving solutes behind

▪ Schematic of functions of tubular excretory organ

▪ Functions of the mammalian kidneyThe Mammalian Urinary System

▪ Functions of the mammalian kidney▸ Regulate major inorganic solutes

R l l l▸ Regulate plasma volume▸ Regulate harmful or un-needed organic molecules▸ Osmotic balance▸ Secretion of erythropoietiny p▸ Secretion of renin▸ Conversion of vitamin D to its active formConversion of vitamin D to its active form▸ Excretion of pheromones

▪ The KidneysThe Mammalian Urinary System

The Kidneys▸ Located on either side of vertebrae, between T12 and L3▸ Left kidney slightly superior to rightLeft kidney slightly superior to right▸ Adrenal glands sit on superior surface of each kidneys▸ Kidneys lie between dorsal body wall and the parietal y y pperitoneum▸ Each kidney is protected and stabilized by:♦ The renal capsule - layer of collagen fibers

♦ The adipose capsule - thick layer of adipose tissue

♦ The renal fascia dense outer layer of collagen fibers♦ The renal fascia - dense outer layer of collagen fibers

▪ The urinary system in a mammalThe Mammalian Urinary Systemy y

▪ Gross anatomy of the human kidneyThe Mammalian Urinary System

▪ Internal anatomy of the human kidneyThe Mammalian Urinary System

▪ Internal anatomy of the human kidney

▪ Gross anatomy of the kidney▸ Renal hilus - prominent medial indentation and point of

f l l d i f i f h entry for renal artery, renal nerves and point of exit for the renal vein▸ Renal sinus - internal cavity within the kidneyy y▸ Renal Cortex - superficial layer in contact with capsule▸ Renal Medulla - inner layer - consists of♦ R l id t i l t t♦ Renal pyramids - triangular structures♦ Renal papilla - projects from the tips of pyramids to sinus♦ Renal columns - separate pyramids

R l l b l id d l i t▸ Renal lobe - renal pyramids and overlying cortex▸ Minor calyx - ducts into which urine drains from papilla▸ Major calyx - collection of two or more minor calycesMajor calyx collection of two or more minor calyces▸ Renal pelvis - funnel-shaped chamber from which urine leaves kidney

▪ Structure of kidneys and urinary systemThe Mammalian Urinary System

▪ Structure of kidneys and urinary system▸ Paired kidneys, lie retroperitoneal

C d f b 1 200 000 f i l i▸ Composed of about 1,200,000 functional units▸ The functional unit is the nephron▸ Each nephron is composed of a glomerulus and a tubule

▪ Functional parts of a nephronThe Mammalian Urinary System

▪ Functional parts of a nephron▸ Nephron - the smallest functional unit capable of the kidney’s basic functionsthe kidney s basic functions

▪ Functional parts of a nephron

Functional parts of a nephron▸ Bowman’s (Glomerular) capsule▸ GlomerulusGlomerulus▸ Proximal tubule▸ Loop of Henlep♦ Descending limb (thick & thin)

♦ Loop

♦ Ascending limb (thin & thick)

▸ Juxtaglomerular apparatus (complex)▸ Di t l t b l▸ Distal tubule▸ Collecting duct

▪ Two types of nephrons in birds & mammalsThe Mammalian Urinary System

▪ Two types of nephrons in birds & mammals▸ Cortical nephrons♦ Originate in cortex♦ Originate in cortex

♦ Glomeruli lie in outer layer of cortex

♦ Hairpin loop only dips slightly into medullary regionp p y p g y y g

♦ Only has peritubular capillaries

▸ Juxtamedullary nephronsy♦ Originate in cortex

♦ Glomeruli lie in inner layer of cortex

♦ Hairpin loop dips plunges deep into medullary region

♦ Peritubular capillaries form vasa recta

▪ Two types of nephronsThe Mammalian Urinary System

▪ Two types of nephrons▸ Juxtamedullary

C i l▸ Cortical

▪ Two types of nephronsThe Mammalian Urinary System

Two types of nephrons▸ Juxtamedullary▸ C ti l▸ Cortical

▪ Cortical nephrons and Juxtamedullary nephronThe Mammalian Urinary System

Cortical nephrons........and Juxtamedullary nephron

▪ Three capillary bedsThe Mammalian Urinary System

Three capillary beds▸ Glomerular♦ Specifically for filtration

♦ Relatively high blood pressure force solutes out of the blood

▸ Peritubular♦ Adapted for absorption♦ Adapted for absorption

♦ Arise from efferent arterioles that drain glomerulus

♦ Low blood pressure

Ab b l & f h b l♦ Absorb solutes & water from the tubules

▸ Vasa recta♦ Long, thin-walledg,

♦ Looping arterioles that follow loop of Henle

♦ Serve juxtamedullary nephrons

▪ Vascular elements of the kidneyThe Mammalian Urinary System

▪ Vascular elements of the kidney

▪ Layers of the glomerular membraneThe Mammalian Urinary System

▪ Layers of the glomerular membrane

▪ Glomerular filtrationThe Mammalian Urinary System

▪ Glomerular filtration▸ Glomerular membrane 100 times more permeable▸ Filters entire plasma volume 65x a day▸ Filters entire plasma volume 65x a day▸ Filters everything except blood cells and most plasma proteinsplasma proteins▸ Fluid passes through 3 layers:♦ Outer wall is fenestrated - endothelial cells♦ Outer wall is fenestrated - endothelial cells

♦ Basement membrane made of collagen & glycoproteins

♦ Inner layer consists of podocytesy p y

▸ Filtrate passes between the cell layers, not through the cells

▪ Glomerular filtration - Forces involvedThe Mammalian Urinary System

▪ Glomerular filtration - Forces involved▸ Glomerular capillary blood pressure

Pl ll id i ▸ Plasma-colloid osmotic pressure▸ Bowman’s capsule hydrostatic pressure▸ Bowman’s capsule osmotic pressure

▪ Pressure drop through kidneysThe Mammalian Urinary System

▪ Pressure drop through kidneys

▪ Glomerular filtration - Forces involved▸ Glomerular capillary blood pressure

Pl ll id i ▸ Plasma-colloid osmotic pressure▸ Bowman’s capsule hydrostatic pressure▸ Bowman’s capsule osmotic pressure

▪ Glomerular filtration - Forces involved▸ Amt of fluid processed♦ B ’ 180 L/d♦ Bowman’s - 180 L/day

♦ Proximal - 54 L/day

♦ Loop Henle 18 L/day♦ Loop Henle - 18 L/day

♦ Urine - 1.5 L/day

▪ Glomerular Filtration Rate (GFR)The Mammalian Urinary System

▪ Glomerular Filtration Rate (GFR)▸ Total amount of filtered fluid per minute▸ Directly proportional to net filtration pressure▸ Directly proportional to net filtration pressure▸ Increase in blood pressure leads to increase in GFR

▪ Factors regulating filtration rate at capillary beds▸ Total surface are for filtration▸ Filtration membrane permeability▸ Net filtration pressure (NFP 17 mmHg)

▪ Control of GFRThe Mammalian Urinary System

▪ Control of GFR▸ Autoregulation - Intrinsic control

R l i f GFR i hi li i▸ Regulation of GFR within limits▸ Myogenic mechanism

▪ Control of GFR▸ Autoregulation - intrinsic control♦ M i h i♦ Myogenic mechanism

– Smooth muscle contracts when stretched - blood vessels

♦ Tubuloglomerular feedbacm mechanism♦ Tubuloglomerular feedbacm mechanism– Involves JG apparatus– Involves macula densa– Increased in tubular flow sensed by macula densa release of vasoactive paracrines constriction of afferent arteriole decreased GFR decreased tubular flow– The paracrines are unclear. Maybe endothelin for vasoconstriction and bradykinin for vasodilation

▪ Control of GFR▸ Autoregulation - Intrinsic control♦ R l ti f GFR ithi li it♦ Regulation of GFR within limits

♦ Tubuloglomerular feedback mechanism

▪ Control of GFR▸ Autoregulation - Intrinsic control♦ R l ti f GFR ithi li it♦ Regulation of GFR within limits

♦ Tubuloglomerular feedback mechanism

Control of GFR▸ Intrinsic response♦ Myogenic responsey g p

– GFR constant at MABP between 80 to 180 mmHg

♦ Tubuloglomerular feedback

GFR tubular flow macula densa send chemical signal to JG cells on– GFR tubular flow, macula densa send chemical signal to JG cells on afferent arteriole causing it to constrict and GFR

▸ Extrinsic response♦ Nervous response

– SNS can decrease GFR

♦ Hormonal response♦ Hormonal response

– Angiotensin II - vasoconstrict arterioles– Prostogalndins - vasodilate arterioles

▪ Tubular Reabsorption may be Active or PassiveThe Mammalian Urinary System

Tubular Reabsorption may be Active or Passive▸ Sodium♦ Active or passivep

♦ Symport - glucose, AA

▸ Water follows sodium♦ Passive

▸ Proteins♦ S ll t♦ Small amounts

♦ Transcytosis

▸ UreaUrea♦ Passive

▪ Tubular Reabsorption may be Active or The Mammalian Urinary System

Passive▸ Transepithelial transport across 5 barriersTransepithelial transport across 5 barriers

▪ Tubular Reabsorption may be Active orThe Mammalian Urinary System

▪ Tubular Reabsorption may be Active or Passive

S di b ti▸ Sodium reabsorption

▪ Active and Passive transport at the PCTThe Mammalian Urinary System

▪ Active and Passive transport at the PCT

▪ The renin-angiotensin-aldosterone systemThe Mammalian Urinary System

▪ The renin-angiotensin-aldosterone system▸ Renin secreted into the blood by JG cells♦ D d bl d N Cl♦ Decreased blood NaCl

♦ Decreased ECF volume

♦ Decreased blood pressure♦ Decreased blood pressure

▸ Converts angiotensinogen to angiotensin II l i i I i d i i II▸ In lungs angiotensin I is converted to angiotensin II

▸ Angiotensin II stimulates the release of aldosterone from the adrenal cortex

▪ The renin-angiotensin-aldosterone systemThe Mammalian Urinary System

▪ The renin-angiotensin-aldosterone system▸ Renin secreted into the blood by JG cells♦ D d bl d N Cl♦ Decreased blood NaCl

♦ Decreased ECF volume

♦ Decreased blood pressure♦ Decreased blood pressure

▸ Converts angiotensinogen to angiotensin II l i i I i d i i II▸ In lungs angiotensin I is converted to angiotensin II

▸ Angiotensin II stimulates the release of aldosterone from the adrenal cortex

▪ OsmoconcentrationThe Mammalian Urinary System

▪ Osmoconcentration▸ The ability to excrete urine of varying concentrations depends on the medullary concentrations depends on the medullary contercurrent-multiplier system▸ R ll▸ Recall♦ Isotonic (isosmotic)

♦ H t i (h ti )♦ Hypotonic (hypo-osmotic)

♦ Hypertonic (hyperosmotic)

L ti l ti di t i th kid▪ Large vertical osmotic gradient in the kidneys

▪ Osmoconcentration▸ Large vertical osmotic gradient in the kidneys

▪ Osmoconcentration▸ Working model of the countercurrent multplier system:system:♦ Assumptions:

– Descending limb highly permeable to H2ODescending limb highly permeable to H2O– Descending limb does not actively transport Na+– Hairpin loop– Ascending limb actively cotransports Na+ and Cl- from lumen– Ascending limb relatively impermeable to H2O– Pump can achieve 200 mOsmol/L maximal difference across the– Pump can achieve 200 mOsmol/L maximal difference across the loop

▪ Osmoconcentration▸ The Countercurrent Multiplier System

A B C D E F

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350350350350

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325325425425

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500500500

300300300500

350350350500

225425400

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▪ Countercurrent Multiplication SystemThe Mammalian Urinary System

▪ Countercurrent Multiplication System

OsmoconcentrationThe Mammalian Urinary System

▸ Recycling of Urea

▸ Excretion of Urine - concentrated urine

▸ Excretion of Urine - diluted urine

▪ Bladder storage and micturitionThe Mammalian Urinary System

▪ Bladder storage and micturition

▪ Bladder storage and micturitionThe Mammalian Urinary System

▪ Bladder storage and micturition

▪ Nephrons from the major classes ofThe Mammalian Urinary System

▪ Nephrons from the major classes of vertebrates

Principles of Animal PhysiologyExcretory SystemExcretory SystemThe Avian Urinary

The Salt Glands of a Gull

Insect Malpighian Tubules

▪ Stop here▪ Stop here▪ Review

11 Animal Physiology - Excretory Systems

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