Which of the following helps to create high medullary osmotic gradient?: (A) Thick ascending loop of henle, (B) Vasa recta, (C) Counter current exchanger system, (D) All of the above
Answer is A. It creats high medullary osmotic gradient.
It is by thick ascending loop of henle, collecting duct

Medullary collecting duct.

It maintains medullary osmotic gradient created by counter current multiplier.
It is by Vasa recta