Antidiuretic hormone (ADH) exerts its primary action on which organ to conserve body water?

Antidiuretic hormone (ADH) exerts its primary action on which organ to conserve body water?

• A. Lungs
• B. Spleen
• C. Kidneys
• D. Heart

Answer: (C)

ADH's main action is in the kidneys, where it increases water reabsorption in the collecting ducts by acting on V2 receptors. This triggers a cAMP-mediated signal that promotes insertion of aquaporin-2 channels into the apical membranes of collecting duct cells, making the tubules more permeable to water. Water moves from the filtrate back into the bloodstream, reducing urine volume and concentrating the urine to conserve body water. Other organs like the lungs, spleen, or heart do not mediate the primary water-conserving effect of ADH; its vasoconstrictive actions via V1 receptors can influence blood pressure, but the kidney is the key site for conserving water.

ADH's main action is in the kidneys, where it increases water reabsorption in the collecting ducts by acting on V2 receptors. This triggers a cAMP-mediated signal that promotes insertion of aquaporin-2 channels into the apical membranes of collecting duct cells, making the tubules more permeable to water. Water moves from the filtrate back into the bloodstream, reducing urine volume and concentrating the urine to conserve body water. Other organs like the lungs, spleen, or heart do not mediate the primary water-conserving effect of ADH; its vasoconstrictive actions via V1 receptors can influence blood pressure, but the kidney is the key site for conserving water.