Major site of action of ADH -

Ans. is 'd' i.e., Medullary collecting duct o In kidney, ADH increase water reabsorption by increasing the permeability of water in late distal tubule, cortical and medullary collecting ducts. ADH has this antidiuretic effect by acting on V2 receptors which augment water reabsorption by aquaporin-2 water channels.o It is worth noting that, though the ADH increases the permeability of water in late distal tubules, cortical collecting duct and medullary collecting duct, the most important action is on medullary collecting duct where the maximum concentration of urine occurs.