Which portion of the nephron is primarily responsible for fine-tuning of sodium and water reabsorption under aldosterone and ADH?

• A. Proximal tubule
• B. Loop of Henle
• C. Distal convoluted tubule and collecting ducts
• D. Glomerulus

Answer: (C)

The part of the nephron that handles the final adjustments in sodium and water reabsorption is the distal convoluted tubule and collecting ducts. Aldosterone acts here to increase sodium reabsorption (and potassium secretion) by upregulating sodium channels and Na+/K+ pumps in principal cells, which directly tunes how much sodium is reclaimed. Antidiuretic hormone targets the collecting ducts to raise their water permeability by inserting aquaporin-2 channels, letting more water follow the reabsorbed sodium when the body needs to conserve water and produce concentrated urine. This combination lets the body finely adjust both sodium balance and water retention.

Earlier segments do bulk reabsorption without hormonal fine-tuning—the proximal tubule reclaims most filtrate in a largely constant manner, and the loop of Henle helps set the concentration gradient but isn’t the primary site of hormonal control. The glomerulus is involved in filtration, not reabsorption.