Renal filtration fraction is calculated as: (A) Renal plasma flow (RPF)/GFR, (B) GFR/RPF, (C) (RPF x GFR)/ Total Blood flow, (D) None of the above
Answer is B. Renal filtration fraction= GFR/(RPF) The filtration fraction, is normally 0.16-0.20. The GFR varies less than the RPF. When there is a fall in systemic blood pressure, the GFR falls less than the RPF because of efferent aeriolar constriction, and consequently the filtration fraction rises.