Which cells in the collecting duct are primarily responsible for water reabsorption when stimulated by ADH?

Which cells in the collecting duct are primarily responsible for water reabsorption when stimulated by ADH?

• A. Intercalated cells
• B. Principal cells
• C. Urothelial cells
• D. Mucous-secreting cells

Answer: (B)

Water reabsorption in the collecting duct in response to ADH is carried out mainly by the principal cells. ADH binds to V2 receptors on these cells, triggering a signaling cascade that causes aquaporin-2 channels to be inserted into the apical membrane. Those water channels dramatically increase the lumen-to-cell permeability, allowing water to move into the cell and then out to the interstitium via aquaporin-3/4 on the basolateral side. This makes the collecting duct highly permeable to water and enables concentration of urine, especially in the medulla where the osmotic gradient is strong. Intercalated cells, by contrast, are focused on acid-base balance (secreting H+ and reclaiming bicarbonate) and are not the primary route for water reabsorption. Urothelial cells line the renal pelvis and ureter, not the collecting duct, and mucous-secreting cells aren’t part of this segment either. Thus the principal cells are the ones responsible for ADH-driven water reabsorption.

Water reabsorption in the collecting duct in response to ADH is carried out mainly by the principal cells. ADH binds to V2 receptors on these cells, triggering a signaling cascade that causes aquaporin-2 channels to be inserted into the apical membrane. Those water channels dramatically increase the lumen-to-cell permeability, allowing water to move into the cell and then out to the interstitium via aquaporin-3/4 on the basolateral side. This makes the collecting duct highly permeable to water and enables concentration of urine, especially in the medulla where the osmotic gradient is strong.

Intercalated cells, by contrast, are focused on acid-base balance (secreting H+ and reclaiming bicarbonate) and are not the primary route for water reabsorption. Urothelial cells line the renal pelvis and ureter, not the collecting duct, and mucous-secreting cells aren’t part of this segment either. Thus the principal cells are the ones responsible for ADH-driven water reabsorption.