Vasopressin decreases the volume of urine primarily by causing:: (A) Decrease in glomerular filtration rate, (B) Decrease in renal blood flow, (C) Decrease in water permeability of descending limb of loop of Henle, (D) Increase in water permeability of collecting duct cells
Answer is D. In the absence of ADH, collecting ducts are impermeable to water. ADH increases the exocytosis and decreases the endocytosis of water channels (aquaporins) in the collecting duct cells. This results in increase in permeability of collecting ducts to water.