Which hormones regulate the permeability of the collecting duct?

Which hormones regulate the permeability of the collecting duct?

• A. ADH and aldosterone
• B. Growth hormone and prolactin
• C. Insulin and glucagon
• D. Thyroid hormone and calcitonin

Answer: (A)

The key concept is how the collecting duct adjusts water movement through hormonal control. The main regulator of water permeability in the collecting duct is ADH (vasopressin). When ADH is present, it binds to receptors on the principal cells, triggering a signaling cascade that moves aquaporin-2 water channels to the apical membrane. With more aquaporin-2 channels, water can move freely from the tubular lumen into the cells and back into the bloodstream, making the urine more concentrated. If ADH is absent, these channels are not inserted, the duct becomes less permeable to water, and more dilute urine results. Aldosterone also affects the collecting duct, but its primary role is to increase Na+ reabsorption by upregulating epithelial sodium channels and Na+/K+ pumps. Since water follows Na+ osmotically, aldosterone indirectly enhances water reabsorption, but it does not directly regulate water permeability via aquaporins like ADH does. The other hormones listed regulate different physiological processes and do not control collecting duct water permeability.

The key concept is how the collecting duct adjusts water movement through hormonal control. The main regulator of water permeability in the collecting duct is ADH (vasopressin). When ADH is present, it binds to receptors on the principal cells, triggering a signaling cascade that moves aquaporin-2 water channels to the apical membrane. With more aquaporin-2 channels, water can move freely from the tubular lumen into the cells and back into the bloodstream, making the urine more concentrated. If ADH is absent, these channels are not inserted, the duct becomes less permeable to water, and more dilute urine results.

Aldosterone also affects the collecting duct, but its primary role is to increase Na+ reabsorption by upregulating epithelial sodium channels and Na+/K+ pumps. Since water follows Na+ osmotically, aldosterone indirectly enhances water reabsorption, but it does not directly regulate water permeability via aquaporins like ADH does. The other hormones listed regulate different physiological processes and do not control collecting duct water permeability.