Which hormone increases sodium reabsorption and potassium secretion in the distal tubule and collecting duct?

• A. Antidiuretic hormone
• B. Renin
• C. Aldosterone
• D. Parathyroid hormone

Answer: (C)

Aldosterone increases sodium reabsorption and potassium secretion in the distal tubule and collecting duct. It acts on principal cells in the late nephron, binding to intracellular mineralocorticoid receptors and boosting the transcription of epithelial sodium channels (ENaC) on the apical membrane and Na+/K+ pumps on the basolateral side. More ENaC channels and more Na+/K+ ATPase activity raise sodium uptake from the tubular lumen into the blood, and the enhanced sodium reabsorption makes the tubular lumen more negatively charged, which drives potassium to move into the lumen and be excreted. Water reabsorption can also increase indirectly because it follows the reabsorbed sodium, but the direct effect described here is on Na+ and K+.

Antidiuretic hormone mainly increases water reabsorption via aquaporins and doesn’t directly raise Na+ reabsorption or K+ secretion. Renin triggers the RAAS cascade that ultimately increases aldosterone release, but the direct effect on the distal nephron is due to aldosterone itself. Parathyroid hormone focuses on calcium reabsorption and phosphate handling in the kidney, not sodium and potassium reabsorption.