Which hormone influences kidney function?

• A. Renin
• B. Bradykinin
• C. Aldosterone
• D. Erythropoietin

Answer: (C)

Aldosterone directly regulates how the kidney handles salts and water. This adrenal cortical hormone acts on cells in the distal tubule and collecting duct to increase the activity and number of sodium channels (ENaC) and the Na+/K+ ATPase pump. The result is more sodium reabsorption from the filtrate into the blood, and water follows, raising blood volume and pressure. Potassium is pushed into the filtrate to be excreted, maintaining electrolyte balance, and hydrogen ion secretion helps with acid–base balance as well.

Renin is an enzyme that initiates the RAAS cascade, indirectly affecting kidney function but not a hormone itself. Bradykinin influences renal blood flow as a vasodilator but is not a primary regulator of tubular transport. Erythropoietin is produced by the kidneys to stimulate red blood cell production, not to control tubular reabsorption or fluid balance.