1. Renal Physiology
Prof. K. Sivapalan.

2. Functions of the Kidney
Maintenance of water and electrolyte balance
Maintenance of acid base balance
Regulation of blood pressure
Excretion of water soluble wastes [liver]
Haemopoisis
Endocrine function
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General and Glomerulus

3. General and Glomerulus
Structure.
There are two kidneys
Retroperitonially.
Cortex
Medulla
Renal pelvis
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General and Glomerulus

4. General and Glomerulus
Nephron.
1.3 million in each kidney
Bowman’s capsule
Glomerulus
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
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General and Glomerulus

5. Types of Nephrons and Blood Vessels
Cocrtical nephrons – 85 % - Urine formation
Juxta-medullary nephrons – 15 % - concentration of urine.
Interlobar artery and vein.
Arcuate artery
Interlobular artery and vein
Peritubular capillaries
Vasarecta.
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General and Glomerulus

6. Pressure in Renal Vessels
Renal artery arises from aorta.
Interlobar artery → arcuate artery → interlobular artery → afferent arteriole – short course to capillaries.
Higher pressure at the arteriolar end – 45 to 50 mm Hg.
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General and Glomerulus

7. General and Glomerulus
Renal Blood low
Resting renal blood flow- 1.2 L/min.
Measured by flow meters or Fick principle.
PAH is filtered and secreted - excreted almost100 % when infused in low doses.
Renal plasma flow = UPAH x V / PPAH
[Urine concentration multiplied by the urinary volume divided by plasma concentration ≈ 600 ml/min]
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General and Glomerulus

8. Regulation of Renal Blood Flow
Autoregulation- at physiological mean arterial pressures of 90 to 220 mm Hg in dog, ? 60 to 180 in human.
Sympathetic- vasoconstriction. [VMC- hemorrhage, exercise etc]
Angeotensin- more on efferent than afferent arteriole.
Reno renal reflex- increase in ureteral pressure in one kidney leads to decrease in efferent activity to the other kidney- ?increase sodium and water excretion by other
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General and Glomerulus

9. General and Glomerulus
Juxta Glomerular Apparatus
Bowman’s capsule is made up of podocytes.
Basment membrane seperates podocytes and endothelium of capillaries.
Fenestrations of the endothelium are 90 nm, podocytes- 25 nm, basement membrane permits 4-8 nm.
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General and Glomerulus

10. Glomerular Filtration
Permeability of the glomerular capillaries is 50 times more than those in skeletal muscle.
Substances below 4 nm diameter are freely filtered. Substances up to 8 nm can be filtered depending on the charge.
Sialoproteins in the capillaries are negatively charged and repel anionic substances.
This is why albumin, 7nm, is not filtered normally and hemaglobin is filtered. In nephritis the negative charge is dissipated and albuminurea occurs.
The filtrate contains all water soluble substances in plasma minus the proteins.
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General and Glomerulus

11. General and Glomerulus
GFR
GFR- glomerular filtration rate- 125 mL / min, 180 L / day
Filtration fraction- ratio of the plasma filtered to 0.20.
Afferent end of the capillaries:
Hydrostatic pressure [out]- 50 mm Hg.
Capsular pressure [in]- 10 mm Hg.
Colloid osmotic pressure [in]- 25 mm Hg.
Efferent end of the capillaries:
Hydrostatic pressure [out]- 45 mm Hg.
Colloid osmotic pressure [in]- 35 mm Hg.
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General and Glomerulus

12. General and Glomerulus
Factors affecting GFR
Capillary hydrostatic pressure-
Systemic blood pressure [autoregulation]
Afferent or efferent arteriolar constriction.
Capsular pressure-
Obstruction to flow
Oedema of the kidney [tight capsule]
Plasma proteins-
Dehydration, hypoalbuminaemia
Capillary permeability-
Effective surface area.
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General and Glomerulus

13. General and Glomerulus
Glomerular Feed Back
Tubuloglomerular feed back- reduction of flow in distal tubule increases GFR and increase reduces GFR.
Sensor is the macula densa. ?Amount of sodium entering macula - ATP usage and adenosine formation resulting afferent arteriolar constriction.
Glomerulo tubular feed back- increase of filtration increases absorption in PCT.
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General and Glomerulus

14. General and Glomerulus
Measuring GFR
It is measured using Fick principle.
Substance used should be only filtered. It should not be secreted or reabsorbed.
It should not be metabolized or excreted by other means giving stable or constant concentration in plasma.
GFR = UV/P
Substances-
Inulin- polymer of fructose not metabolized.
Creatinine- endogenous from muscle, little is absorbed and secreted.
Urea- reabsorption varies with urine flow.
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General and Glomerulus