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Glomerular Filtration rate and its determinants.pptx
- 1. GLOMERULAR FILTRATION By Prof. Dr. NusratTariq 4/17/2024 1
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- 3. LEARNING OBJECTIVES By theend 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) GlomerularFiltration 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 • Thefiltrate is devoid of proteins and RBC • The concentration of filtrate is similar to ?????. 4/17/2024 5
- 6. GLOMERULAR FILTRATE • Thefiltrate 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 • Filtrationfraction 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 causingfiltration 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=Kfx 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 CapillaryFiltration 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. 1)INCREASED GLOMERULAR CAPILLARY FILTRATION COEFFICIENTINCREASES 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. 1)INCREASED GLOMERULAR CAPILLARY FILTRATIONCOEFFICIENT 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
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- 20. 2-INCREASED BOWMANS HYDROSTATIC PRESSUREINCREASES 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 GLOMERULARCAPILLARY 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 CAPILLARYHYDROSTATIC 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 AFFECTINGTHE 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 CONTRACTIONOR 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 CANDECREASE GFR • Kf in DM, HTN, renal diseases • PB in urinary tract obstruction • Glomerular Capillary oncotic pressure due to RBF or in plasma proteins 4/17/2024 26
- 27. FACTORS WHICH CANDECREASE 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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