Autoregulation of glomerular filtration rate and renal blood

Autoregulation of GFR and Renal Blood Flow

1. Autoregulation of glomerular filtration rate and renal blood flow Prepared by: Deepa Devkota Roll no:07 Human Biology 7 th batch

2. Overview Introduction: Glomerular filtration rate renal blood flow Autoregulation of GFR and renal blood flow Tubuloglomerular feedback mechanism Myogenic autoregulation Importance of Autoregulation

3. Introduction Glomerular filtration rate (GFR): Rate at which plasma is filtered from the glomerular capillaries into bowman’s capsule per unit time. In average, GFR is about 125ml/min or 180 l/day and filtration fraction is about 0.2(20%)

4. Renal blood flow In an average 70 kg man: renal blood flow is about 1100ml/min (22% of cardiac output) To supply enough plasma for high rate of glomerular filtration for the precise regulation of body fluid volumes and solute concentration Renal blood flow= renal artery pressure-renal vein pressure total renal vasculature resistance Renal arterial pressure is about equal to systemic arterial pressure but the pressure of renal veins averages about 3-4 mm Hg Most of the renal vascular resistance resides in interlobular arteries, afferent and efferent arterioles.

5. Autoregulation of GFR and renal blood flow Effective intrinsic feedback mechanism for the maintenance of renal blood flow and GFR despite marked change in arterial blood pressure Relatively constant over an arterial pressure range between 80 and 170 mm Hg

6. Tubuloglomerular feedback mechanism Links the change in sodium chloride concentration at macula densa with the control of renal arteriolar pressure Helps to ensure a relatively constant delivery of sodium chloride to distal tubule and helps to prevent spurious fluctuation in renal excretion. Has two components that act together to control GFR: Afferent arteriolar feedback mechanism Efferent arteriole feedback mechanism

7. Efferent arteriole feedback mechanism Efferent arteriole vasoconstriction causing increase in glomerular hydrostatic pressure

8. Contd … Angiotensin II act on adrenal gland to release aldosterone Aldosterone stimulates the epithelial cells of the distal tubule and collecting ducts of kidney to increase reabsorption of sodium in exchange of potassium RAS act on CNS for the secretion of vasopressin(ADH) from posterior pituitary gland to increase water intake by stimulating thirst, reduce urinary loss by concentrating urine

9. Contd.. The afferent and efferent arterioles are innervated by sympathetic neurons . Norepinephrine is released by sympathetic nerve and circulating epinephrine by adrenal medulla, causing vasoconstriction by binding to α 1 adrenoreceptor . Macula densa cells also secrete nitric oxide which puts brake on the action of ATP and adenosine at afferent arteriole

10. Afferent arteriole feedback mechanism

11. Adjustment in renal arteriole caliber to alter GFR and renal blood flow

12. Tubuloglomerular feedback mechanism

13. Myogenic autoregulation of renal blood flow and GFR Ability of individual blood vessels(small arterioles) to resist wall stretching during increased arterial pressure Prevents excessive increase in GFR and renal blood flow

14. Contd.. this pressure sensitive mechanism has no direct means of detecting change in renal blood flow and GFR May be important in protecting kidney from hypertension induced injury

15. Importance of Autoregulation in preventing extreme change in renal excretion In the absence of autoregulation, an increase of blood pressure (from 100 to 125 mm Hg ) would cause about 25% increase in GFR(180l/day to 225l/day) If the tubular reabsorption remained constant, it causes an increase in urine flow to 46.5l/day (30 folds increase) Since plasma volume is only about 3l, it causes quick depletion of blood volume Even with these special control mechanism, change in arterial pressure have significant effect on renal excretion of water and sodium known as pressure natriuresis or pressure diuresis

16. References Guyton and hall, textbook of medical physiology,12 th edition Johnson Leonard R., essential medical physiology,3 rd edition William F. Ganong ,review of medical physiology ,23 rd edition Bern and Levy,physiology,5 th edition