This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Glomerular Filtration, Renal Blood Flow, and Their Control, Subject name: Physiology
Percentage of GFR to renal plasma flow: 
Select and explain. 
A. a.. 20%, B. b. 38%, C. c. 50%, D. d. 60%
A: a.. 20%
Answer: A: a.. 20% 
Explanation: Ans. (a) 20%Ref: Guyton's physiology 11th ed. / 316* GFR Is About 20 Per Cent of the Renal Plasma Flow.* In an average adult GFR is about 125 ml/min, or 180 L/ day.* Renal plasma flow is 650ml/min* The filtration fraction is calculated as follows: Filtration fraction = GFR/Renal plasma flow* Therefore125ml/min------------650ml/min= 0.2* The fraction of the renal plasma flow that is filtered (the filtration fraction) averages about 0.2; this means that about 20 per cent of the plasma flowing through the kidney is filtered through the glomerular capillaries.Also Know* The entire plasma volume is only about 3 liters, whereas the GFR is about 180 L/day, the entire plasma can be filtered and processed about 60 times each day.