Physiology – MCQ 53 – Driving force for counter current multiplier system

The prime driving force for counter current multiplier system is:
A. Medullary hyperosmolarity
B. Reabsorption of Na+ in thick ascending limb
C. Action of ADH via aquaporin channels
D. Urea recycling

Correct answer : B. Reabsorption of Na+ in thick ascending limb

The primary driving force is reabsorption of Na+ in thick ascending limb. Medullary hyperosmolarity is an effect produced by the countercurrent multiplier system.