Glomerular Filtration rate and its determinants.pptx

The first step in urine formation is filtration of large
amounts of fluid through the glomerular capillaries into
Bowman’s capsule—almost 180 L/day. Most of this fil�trate is reabsorbed, leaving only about 1 liter of fluid to be
excreted each day, although the renal fluid excretion rate
is highly variable, depending on fluid intake. The high rate
of glomerular filtration depends on a high rate of kidney
blood flow, as well as the special properties of the glomerular capillary membranes.

1. GLOMERULAR FILTRATION By Prof. Dr. Nusrat Tariq 4/17/2024 1

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3. LEARNING OBJECTIVES By the end of this lecture you should be able to: Define GFR Describe the determinants of GFR Explain the factors affecting GFR Discuss the hormones and autocoids that affect GFR 4/17/2024 3

4. GLOMERULAR FILTRATION RATE (GFR) Glomerular Filtration Rate is defined as volume of filtrate formed each minute by both Kidneys. Normal/ Average Adult GFR = 120 - 125 ml/ min or 180L/day 4/17/2024 4

5. GLOMERULAR FILTRATE The filtrate is devoid of proteins and RBC The concentration of filtrate is similar to ?????. 4/17/2024 5

6. GLOMERULAR FILTRATE The filtrate is devoid of proteins and RBC The concentration of filtrate is similar to plasma . 4/17/2024 6

7. RENAL BLOOD FLOW Renal blood Flow is 22% of the cardiac output or 1100 ml/min Renal plasma flow is 55% of the RBF approximately 600ml/min GFR is 20% of the renal plasma flow 4/17/2024 7

8. FILTRATION FRACTION Filtration fraction is the fraction of plasma which is filtered. Filtration fraction =GFR/RPF =125/600 = 0.2 4/17/2024 8

9. DETERMINANTS OF THE GFR GFR = Kf × Net filtration pressure 4/17/2024 9

10. FILTRATION COEFFICIENT ( KF) Kf = the product of the hydraulic conductivity and surface area of the glomerular capillaries. GFR = Kf × Net filtration pressure Kf =???? 4/17/2024 10

11. FILTRATION COEFFICIENT ( KF) GFR = Kf × Net filtration pressure Kf = GFR/Net filtration pressure 4/17/2024 11

12. NET FILTRATION PRESSURE forces causing filtration by the glomerular capillaries ?????? 4/17/2024 12

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14. NET FILTRATION PRESSURE sum of capillary hydrostatic pressure minus the colloid osmotic pressure plus the bowman's capsular pressure 60-(32+18)=10mmHg Capillary hydrostatic pressure is the outward force (60 mmHg) Colloid osmotic and bowmans pressure are inward forces (32mmHg+18mmHg) 4/17/2024 14

15. DETERMINANTS OF GFR GFR= K f x net filtration pressure Net filtration pressure depends on three forces 1. capillary hydrostatic pressure 2. capillary colloid osmotic pressure 3. bowman's capsular pressure 4/17/2024 15

16. 1)Increased Glomerular Capillary Filtration Coefficient ( Kf ) Increases GFR 2) Increased Bowman’s Capsule Hydrostatic Pressure Decreases GFR 3) Increased Glomerular Capillary Colloid Osmotic Pressure Decreases GFR 4) Increased Glomerular Capillary Hydrostatic Pressure Increases GFR 4/17/2024 16

17. INCREASED GLOMERULAR CAPILLARY FILTRATION COEFFICIENT INCREASES GFR Kf = GFR/Net filtration pressure Total GFR = 125 ml/min Net filtration pressure = 10 mm Hg The normal Kf is = 12.5 ml/min /mmHg of filtration pressure. 4/17/2024 17

18. INCREASED GLOMERULAR CAPILLARY FILTRATION COEFFICIENT INCREASES GFR Some diseases lower Kf by Reducing the number of functional glomerular capillaries(thereby reducing the surface area for filtration) Increasing the thickness of the glomerular capillary membrane and (reducing its hydraulic conductivity). 4/17/2024 18

19. Example: chronic, uncontrolled Hypertension diabetes mellitus 4/17/2024 19

20. 2-INCREASED BOWMANS HYDROSTATIC PRESSURE INCREASES GFR Stones that lodge in the urinary tract obstruct outflow of the urinary tract and raise the Bowman’s capsule pressure causing reduction of GFR. . 4/17/2024 20

21. 3) INCREASED GLOMERULAR CAPILLARY COLLOID OSMOTIC PRESSURE DECREASES GFR Filtration fraction = GFR/Renal plasma flow = (125ml/m)/(650ml/m) = 0.2 Increases in the filtration fraction increases the plasma colloid osmotic pressure as the proteins are concentrated in the glomerular capillary 4/17/2024 21

22. 4) INCREASED GLOMERULAR CAPILLARY HYDROSTATIC PRESSURE INCREASES GFR Glomerular hydrostatic pressure is determined by three variables: (1) arterial pressure, (2) afferent arteriolar resistance, and (3) efferent arteriolar resistance. Constriction of afferent arterioles reduces GFR. Modest efferent constriction raises GFR, but Severe efferent constriction tends to reduce GFR. 4/17/2024 22

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24. OTHERS FACTORS AFFECTING THE GFR Changes in renal blood flow  Changes in systemic blood pressure   Afferent or efferent arteriolar constriction Edema of kidney inside tight renal capsule Changes in concentration of plasma proteins: dehydration, hypoproteinemia, etc (minor factors) Changes in glomerular capillary permeability   Changes in effective filtration surface area . Contraction of mesangial cells: Decreases GFR by reducing the Kf due to reduction in surface area for filtration    4/17/2024 24

25. AGENTS CAUSING CONTRACTION OR RELAXATION OF MESANGIAL CELLS. Contraction Relaxation Endothelins ANP Angiotensin II Dopamine Vasopressin PGE2 Norepinephrine cAMP Thromboxane A2 Histamine 4/17/2024 25

26. FACTORS WHICH CAN DECREASE GFR  K f in DM, HTN, renal diseases P B in urinary tract obstruction Glomerular Capillary oncotic pressure due to RBF or in plasma proteins 4/17/2024 26

27. FACTORS WHICH CAN DECREASE GFR  Glomerular hydrostatic pressure 1.  Arteial Blood Pressure 2.  angiotensin II 3. sympathetic stimulation leading to vasoconstiction  RBF in afferent arteriole 4/17/2024 27

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