Aldosterone primarily acts on which organ to regulate electrolyte and water balance?

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

Answer: (D)

Aldosterone regulates electrolyte and water balance by acting on the kidneys. It binds to mineralocorticoid receptors in the principal cells of the distal tubule and collecting ducts, increasing the production of epithelial sodium channels (ENaC) and the Na+/K+ ATPase. This boosts sodium reabsorption from the tubular lumen into the blood, and potassium is excreted into the urine. Water follows the reabsorbed sodium by osmosis, helping to maintain blood volume and pressure. The kidneys are the primary organ where this hormonal action controls electrolyte levels and water balance; other organs don’t regulate these processes through aldosterone in the same direct way.