This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Excretory System (Kidney, Bladder) Acid-Base Balance, Subject name: Physiology
Renal filtration fraction is calculated as 
Select and explain. 
A. Renal plasma flow (RPF)/GFR, B. GFR/RPF, C. (RPF x GFR)/ Total Blood flow, D. None of the above
B: GFR/RPF
Answer: B: GFR/RPF 
Explanation: 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.