The primary driving force for counter current Multiplier system is:(2018): (A) Medullary hyperosmolarity, (B) Reabsorption of Na+ in thick ascending limb, (C) Action of ADH aquaporin channels, (D) Urea recycling
Answer is A. Concentrating mechanism depends on the maintenance of a gradient of increasing osmolality along the medullary pyramids. This gradient is produced by the operation of the loops of Henle as countercurrent multipliers and maintained by the operation of the vasa recta as countercurrent exchangers. Ref:- Ganong, pg num:- 685