factors affecting glomerular filtration rate .pptx

Factors affecting glomerular filtration rate . Students reference

1. Factors affecting GRF Dr Shamshad

2. Objectives D escribe the components and functions of nephron Discuss how arterial diameter affects nephron function Discuss how blood pressure affects nephron function Explain the process of reabsorption Explain the role of carriers in glucose reabsorption Identify the actions of ADH and aldosterone on solute reabsorption and water uptake prerequisite materials and equipment.

3. Glomerular F unction T est Renal clearance tests Tests for glomerular functions Tests for tubular function: uremia Others Renal Function Test done : To assess the functional capacity of the kidneys To detect the renal impairment as

4. Renal clearance tests Glomerular functions Test Inulin clearance Creatinine clearance Other : IVP Artiography USG Isotope perfusion studies Renal biopsy Test for tubular functions PAH clearance Urea clearance PSP excretion test Measurement of water reabsorption Other: micropuncturing Stop flow technique Microcryoscopic studies Microelectrode studies

5. Definition : Clearance of a certain substance is the volume of plasma cleared from this substance per unit time (minute). Calculation: According to law of conservation of mass: Ux *volume of urine/minute=GFR* Px C=excretion rate/plasma concentration The mass of substance (X) extracted from plasma / minute = concentration of substance (X) in plasma (PX) X the volume of plasma which is cleared from this substance / minute (CX ).

6. Glucose clearance All the filtrated glucose is reabsorbed at plasma concentration below 250mg/dl. Clearance of glucose is zero below 250mg/dl. Glucose appear in urine at about 250mg/minute . The reabsorption becomes saturated at plasma concentration above 350mg/dl. This is maximum transport rate (TM) =375mg/min.

7. The point at which the glucose appear in urine is threshold . and transport maximum is called splay. The renal handling of the glucose curve, the Tm is approached gradually along a curve, rather than abruptly with a sharp deflection The curve is called as splay. Transport maximum of glucose

8. Measurement of reabsorption Rate of reabsorption of a solute Ts Is the difference between the product of GFR and substance in plasma and the rate of its excretion Ts =(GFR*Ps)-(Us* vol ) Unit: mg/minute

9. Measurement of Secretion The rate of secretion of a solutes Ts , is the difference between the rate of excretion Us*V, and the rate of filtration, GFR*PS Ts =(Us*V)-(GFR*Ps)m/minute.

10. According to substance selected; clearance may be used for: 1- Measurement of glomerular filtration rate (GFR): Clearance of inulin or creatinine. 2- Measurement of renal plasma flow (RPF): Clearance of PAH. 3- Measurement of reabsorptive capacity of renal tubules: Transport maximum of glucose (TMG). 4- Measurement of secretory capacity of renal tubules : Transport maximum of PAH (TMPAH ). 5-

11. 5- Mode of handling of substance by the kidney: Clearance ratio and fraction excretion. 6- Assessment of diluting capacity of the kidney: Free water clearance. 7- Assessment of concentrating capacity of the kidney : Free water reabsorption

12. Measurement of GFR Substance used to measure GFR should apply the following conditions : 1- Non-toxic. 2- Does not affect GFR or RPF. 3- Not metabolized by the body or the kidney. 4- Freely filtered: of small molecular weight and not bound to plasma proteins 5- Neither reabsorbed nor secreted. 6- Accurately measured in plasma and urine .

13. Two substances were used: 1:Inulin (Exogenous): Polymer of fructose. Given by IV drip & not orally as it is digested in the intestine. GFR = Cin = 125 ml./min . Advantages: Accurate hence it is used for experimental studies. Disadvantages: Exogenous (need a method of administration)

14. 2:Creatinine (endogenous): End product of creatine metabolism in skeletal muscles. - GFR = CCr = 140 ml./min. Advantage : Endogenous . Disadvantage : Slightly secreted in PCT .Certain drugs affect the secretion . Hence GFR measured by this method is 10% higher than GFR measured by inulin clearance. Clearance Ratio:

15. Measurement of renal blood flow : Substance used to measure renal plasma flow should apply the following conditions: 1- Non-toxic. 2- Does not affect GFR or RPF. 3- Its unbound fraction is freely filtered. 4- Completely secreted not reabsorbed. 5- Accurately measured in plasma and urine. Substance used is Para amino hippuric acid (PAH): RPF = CPAH = Some plasma supplies the non-functioning kidney structures, which include capsule, pelvis and perinephric fat .

16. Plasma concentration of substance Px *clearance of subx Cx = Ux *V GFR= Cx = Ux *V/ Px Effective renal plasma flow=GFR Effective RBF=ERBF= Cx =EFPF/1-Hct Renal blood flow=RBF=ERBF/Extraction ratio Extraction ratio=Atrial x-Venous x/Atrial x

17. The fraction of plasma which is actually cleared is known from “Extraction Ratio” Extraction ratio =Excretion rate/presentation rate So, renal plasma flow calculated by CPAH is only the effective RPF (ERPF). The true RPF equals TRPF = When Hematocrit value ( Hct ) is known: Renal blood Flow (RBF) = Effective renal blood flow/extraction ratio