Antidiuretic hormone (ADH) acts on the kidneys to:

Antidiuretic hormone (ADH) acts on the kidneys to:

• A. Increases water reabsorption in collecting ducts
• B. Decreases renal perfusion
• C. Increases urine volume
• D. Stimulates aldosterone release

Answer: (B)

ADH’s main action is to conserve body water by increasing water reabsorption in the kidney’s collecting ducts. It binds to V2 receptors on principal cells, prompting the insertion of aquaporin-2 channels into the apical membrane. With more water channels present, water moves readily from the filtrate back into the bloodstream, which decreases urine volume and makes the urine more concentrated. This is why ADH tends to reduce how much urine is produced, not increase it, and it does not directly lower renal perfusion. Aldosterone release is not driven by ADH; it’s controlled mainly by the renin-angiotensin-aldosterone system and potassium levels. In short, ADH acts to reabsorb water in the collecting ducts, leading to concentrated, reduced-volume urine.

ADH’s main action is to conserve body water by increasing water reabsorption in the kidney’s collecting ducts. It binds to V2 receptors on principal cells, prompting the insertion of aquaporin-2 channels into the apical membrane. With more water channels present, water moves readily from the filtrate back into the bloodstream, which decreases urine volume and makes the urine more concentrated. This is why ADH tends to reduce how much urine is produced, not increase it, and it does not directly lower renal perfusion. Aldosterone release is not driven by ADH; it’s controlled mainly by the renin-angiotensin-aldosterone system and potassium levels. In short, ADH acts to reabsorb water in the collecting ducts, leading to concentrated, reduced-volume urine.