glomerular filteration rate

1. DETERMINATION OF GFR
• Glomerular filtration rate: It is a test use to see how well
your kidneys are working.
Each day human kidney filter 180 liter fluid but most of it is
reabsorbed so remain 1 liter.
It increase or decrease in different pathologies.

2. DETERMINANTS OF GFR:
 GFR=Kf x net filtration pressure.
Kf is the product of filtration and surface area of glomerular
capillaries. Net filtration pressure is = PG+PB+πg+πb.
Pb is the hydrostatic pressure of Bowman’s capsule it oppose the
flow of plasma.
Pg is the hydrostatic pressure of glomerular capillaries which
allows the flow

3. •πb is colloidal osmotic pressure of proteins in Bowman’s capsule
which allows flow.
πg is colloidal osmotic pressure of proteins in glomerular
capillaries plasma it oppose the flow.
efferent arteriolar resistance.
Afferent arteriolar resistance.
Arterial pressure

4. FLUCTUATIONS IN GFR IN DIFFERENT CONDITIONS:
• urinary tract obstruction cause decrease in GFR by increasing
PB. low blood pressure
decrease the GFR by decreasing Pg.
low sodium ,lowers GFR.
Diabetes increases the GFR.
High protein intake increases the GFR

5. Sympathetic stimulation decreases the GFR.
Toxemia of Pregnancy decreases the GFR.
Acute and chronic failure decreases the GFR.
Prostaglandins increase GFR by releasing stenosis of
afferent arteriole.
Atherosclerosis involve vascular endothelium damage
leads to Endothelin production leads vasoconstriction
and decrease GFR.

6. TECHNIQUES TO DETERMINE GFR:
• For the determination of GFR the substance must be filtered
completely but not reabsorbed and secreted. There is one non
endogenous substance and a endogenous substance to
determine GFR. Inulin in urine.
Creatinine in serum

7. INULIN IN URINE :
• It is totally cleared from plasma and neither reabsorbed nor
secreted. It can be used in search work to see the effect of
different factors on GFR.
It is continuously infused in rats by femoral vein to maintain the
plasma concentration

8. • Formula used to determine GFR.
Clearance=urine concentration x flow
rate/ plasma concentration.
After 20 minutes we will take urine
sample and note the result
Practically we cannot use inulin
because we have to infuse it
continuously

9. CREATININE TEST:
• it is an endogenous substance which is by product of muscle
destruction.
it is used to determine the GFR in labs
it shows how well are kidneys working.
it is slightly reabsorbed in kidneys.
its serum level is tested by taking blood sample.
formula to calculate.
 eGFR=[(40-age x Wt/(0.814 x S.Cr in µmol / L)] x (0.85
if female).
Normal values for men = 85-125 ml/min.
For female = 75-116 ml/min.