The primary driving force for counter current Multiplier system is:(2018)
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
Medullary hyperosmolarity
Reabsorption of Na+ in thick ascending limb
Action of ADH aquaporin channels
Urea recycling
Renal physiology