This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Countercurrent mechanism is not seen in: 
Select and explain. 
A. Kidney, B. Testes, C. Eye, D. Intestine
C: Eye
Answer: C: Eye 
Explanation: Ans: C. Eye(Ref Ganong 25/e p417, 420, 685, 24/e p687, 419, 422) .Countercurrent mechanism:Not seen in eye.Inflow runs parallel to, counter to & in close proximity to outflow for some distance.Seen in kidney, limbs, testis & intestine.In renal system - Both loops of Henle & vasa recta in renal medulla.Intestine - Villi where oxygen directly diffuses from aerioles to vein.