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RENAL PHYSIOLOGY
DR SYED SHAHID HABIBMBBS DSDM FCPSAssociate ProfessorDept. of Physiology
College of Medicine & KKUH
DR SYED SHAHID HABIBMBBS DSDM FCPSAssociate ProfessorDept. of Physiology
College of Medicine & KKUH
1) Introduction2) Glomerular Filtration3) Tubular Processing4) Urine Concentrating
Mechanism5) Micturition
Renal Physiology
RENAL PHYSIOLOGY
TUBULAR PROCESSINGTUBULAR
REABSORPTION & SECRETION
URINE COMPOSITIONURINE COMPOSITION
pHpH usually acidic (pH 6) usually acidic (pH 6) range= 4.8 - 7.5range= 4.8 - 7.5
ColourColour Bright Yellow & Bright Yellow & transparenttransparent
VolumeVolume 1 - 2 L per day1 - 2 L per day
GlucoseGlucose NoneNone
REABSORTION PATHWAYS
Urinary Excretion Rate = Filtration Rate – Reabsorption Rate + Secretion RateUrinary Excretion Rate = Filtration Rate – Reabsorption Rate + Secretion Rate
inulininulin ureaurea
glucgluc CreatCreat
GlucoseUrea
% of Filtered Load Reabsorbed
Glucose (g/day) 100Bicarbonate (mEq/day) >99.9Sodium (mEq/day) 99.4Chloride (mEq/day) 99.1Potassium (mEq/day) 87.8Urea (g/day) 50Creatinine (g/day) 0
PROXIMAL CONVOLUTED TUBULE•many mitochondria •brush border•tight junctions•lateral intercellular spaces.
GLUCOSE AND AMINO ACID REABSORPTION IN NEPHRON
TUBULAR TRANSPORT MAXIMUM
• The Maximum limit/rate at which a solute can be transported across the tubular cells of kidneys is called TUBULAR TRANSPORT MAXIMUM
Tm for Glucose is 375 mg/min
GLUCOSE REABSORPTION
•FBG=60-110 mg/dlFBG=60-110 mg/dl•RBG=110-200 RBG=110-200 mg/dlmg/dl
Transport maxTransport max375 mg/min375 mg/min
Renal ThresholdRenal Threshold 200mg/dl200mg/dl
HYDROGEN
•Secreted in Proximal Tubule and LOH by Counter Transport with Na
Na-H COUNTER Na-H COUNTER TRANSPORTTRANSPORT
Luminal MembraneLuminal Membrane
PCT & LOHPCT & LOH
CotransportNa
G
CotransportNa
AA
CountertransportNa
H+
Cl-
water water Reabsoprtion Reabsoprtion
65%65%
PCTPCT
ATP
Na
K
SODIUM HANDLING
Na+ moves by co transport or exchange from the tubular lumen into tubular epithelial cells
From cells into interstitium it moves by primary active transport
In DCT and CT it is under hormonal control
SODIUM HANDLING
Renal tubular reabsorption Solute reaborption in the proximal tubule
is isosmotic (water follows solute osmotically and tubular fluid osmolality remains similar to that of plasma).
65% of water and sodium reabsorption occurs in the proximal tubule100% of glucose & amino acids
Proximal tubules: coarse adjustment Distal tubules: fine adjustment
(hormonal control).
THIN LOOP OF HENLE•few mitochondria•flattened with few microvilli
THIN DESCENDING LOOP OF HENLE•few mitochondria•flattened with few microvilli
SolutesSolutes
HH22OO
THICK ASCENDING LOOP OF HANLE AND EARLY DCT
Many mitochondria and microvilli, but fewer than in the proximal tubule
ASCENDING LOOP OF HENLEMany mitochondria and microvilli, but fewer than in the proximal tubule
SolutesSolutes
HH22OO
ECF LumenEpithelial Cells
Events inEvents inThickThickALOHALOH
Sodium potassium 2 chloride co transport
Absorption through loop of Henle:Descending limb: is water permeable and allow absorption of 15% of filtered H2O. It is impermeable to Na-CL.
Thin ascending limb: is impermeable to H2O, but permeable to Na-Cl, where they are absorbed passively in this part .
Thick ascending limb: is impermeable to H2O. Na-K-2Cl co-transport occur in this part (25% of Na).
HYDROGEN•Secreted in Proximal Tubule and LOH by Counter Transport with Na
Na-H COUNTER Na-H COUNTER TRANSPORTTRANSPORT
Luminal MembraneLuminal Membrane
PCT & LOHPCT & LOH
ASCENDING LOOP OF HENLE
LATE DCT AND CORTICAL COLLECTING DUCT
• Mitochondria and microvilli decrease. • Principal Cells (Na Abs and ADH related Water abs)• Intercalated Cells (Acid Sec and HCO3 Transport)
DCT AND COLLECTING DUCT
•Principal Cells (Water reabsortion)•Intercalated Cells (Acid Secretion)
I CellI Cell
P CellP Cell
Events Events inin
DCTDCT
Intercalated cell
Events inEvents inDCT & CTDCT & CT
Principal Cell
Events inEvents inDCT & CTDCT & CT
AldosteroneAldosterone
Distal convoluted tubule and collecting ducts
• What happens here depends on hormonal control:
• Aldosterone affects Na+ and K+
• ADH – facultative water reabsorption
FACTORS AFFECTING ADH
Increase ADH Decrease ADH↑Osmolarity ↓Osmolarity
↓ Blood volume ↑ Blood volume↓ Blood
pressure ↑ Blood pressure
Clinical applications
• Thiazide diuretics
• Loop diuretics:
• K+ sparring diuretics:
MEDULLARY COLLECTING DUCT
REABSORPTION OF WATER IN DIFFERENT SEGMENTS OF TUBULES
PART OF NEPHRON PERCENTAGE
REABSORBEDProximal tubules 65
Loop of Henle 15
Distal tubules 10
Collecting ducts 9.2
Passing into urine 0.8
RENAL PHYSIOLOGY
TUBULAR SECRETION
DR SYED SHAHID HABIB
MBBS, FCPS
TUBULAR SECRETION
• Tubular Secretion may be by Passive or Active Mechanisms
• The most important secretory processes are for H, K and Organic Ions
HYDROGEN
• Secreted in Proximal Tubule by Counter Transport with Na
• In DCT and CT it is secreted by Hydrogen ATP ase
• When body fluids are more acidic H secretory process is accelerated and Vice Versa
HYDROGEN
•Secreted in Proximal Tubule and LOH by Counter Transport with Na
•Secreted in DCT by H ATP ase Primary Active Transport
Na-H COUNTER Na-H COUNTER TRANSPORTTRANSPORT
Luminal MembraneLuminal Membrane
PCT & LOHPCT & LOH
I Cell in DCT
RENAL PHYSIOLOGY COUNTER CURRENT
MECHANISM
COUNTER CURRENT MECHANISM
• KIDNEYS HAVE – MECHANISMS FOR
EXCRETING EXCESS WATER– MECHANISMS FOR
EXCRETING EXCESS SOLUTES
NEPHRON TYPES
Superficial (cortical) [85 %]o Capable of forming dilute urine
Juxtamedullary [15 %]o Capable of forming
concentrated (> 300 mOsm/kg) urine
EXCRETION LIMITS
• At least 600 mmol of solutes must be excreted each day – minimum volume = 600/1200 = 0.5L
– maximum volume = 20 Liters
EXCRETION LIMITS
COUNTER CURRENT MECHANISM
• LOOPS OF HENLE OF JUXTA MEDULLARY NEPHRONS establish hyperosmolality of interstitium of medulla. They are called COUNTER CURRENT MULTIPLIERS
• VASA RECTA maintain hyperosmolality established by counter current multipliers. They are called COUNTER CURRENT EXCHANGERS
400
300 300
300
300 200300
300 250300
400 300400
500 400500
700 600700
600 500600
800 800800
1200 12001200
1000 10001000
Cortex
Medulla
OsmolalityOsmolality
DISORDERS OF URINARY CONCENTRATING ABILITY
• Failure to Produce ADH: "Central" Diabetes Insipidus.
• Inability of the Kidneys to Respond to ADH: "Nephrogenic"
Diabetes Insipidus.
RENAL PHYSIOLOGY
MICTURITION
DR SYED SHAHID HABIBMBBS DSDM FCPSAssistant ProfessorDept. of Physiology
College of Medicine & KKUH
DR SYED SHAHID HABIBMBBS DSDM FCPSAssistant ProfessorDept. of Physiology
College of Medicine & KKUH
MICTURITION
It is the process by which the urinary bladder empties when it
becomes filled
Filling of bladder.Micturition reflex.Voluntary control.
Nervous Connections of the Bladder
Urogenital diaphragm
Micturition Reflex
• Actions of the internal urethral sphincter and the external urethral sphincter are regulated by reflex control center located in the spinal cord.– Filling of the urinary bladder activates the stretch receptors,
that send impulses to the micturition center.• Activates parasympathetic neurons, causing rhythmic
contraction of the detrusor muscle and relaxation of the internal urethral sphincter.
– Voluntary control over the external urethral sphincter.
• When urination occurs, descending motor tracts to the micturition center inhibit somatic motor fibers of the external urethral sphincter.
AUTONOMIC SPINAL REFLEX
Nerves Characteristic Function
1 Pelvic nerves (parasympathetic fibers)S-2 and S-3
Both sensory and motor nerve fibers
Contraction of bladder The sensory fibers detect the degree of stretch in the bladder wall
2 Pudendal Nerve somatic nerve Fibers that innervate and control the voluntary skeletal muscle of the sphincter
3 Hypogastric Nerves
sympathetic innervation (L2)
Stimulate mainly the blood vessels and have little to do with bladder contraction. Sensory nerve fibers of the sympathetic nerves also mediate the sensation of fullness and pain.
INNERVATION OF THE BLADDER
CYSTOMETROGRAM
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