How does antidiuretic hormone (ADH) affect the permeability of the collecting ducts to water?

• A. ADH has no effect on the permeability of the collecting ducts to water.
• B. ADH increases the permeability of the collecting ducts to sodium, not water.
• C. ADH decreases the permeability of the collecting ducts to water, reducing water reabsorption.
• D. ADH increases the permeability of the collecting ducts to water, allowing more water to be reabsorbed.

Answer: (D)

Verified step by step guidance

1. Understand the role of antidiuretic hormone (ADH) in the body. ADH is a hormone produced by the hypothalamus and stored in the posterior pituitary gland. It plays a crucial role in regulating water balance in the body.
2. Recognize the target site of ADH action. ADH primarily affects the kidneys, specifically the collecting ducts, which are part of the nephron responsible for the final concentration of urine.
3. Learn how ADH affects the collecting ducts. ADH increases the permeability of the collecting ducts to water by promoting the insertion of water channels called aquaporins into the cell membranes of the duct cells.
4. Understand the physiological effect of increased water permeability. When the collecting ducts become more permeable to water, more water is reabsorbed from the urine back into the bloodstream, concentrating the urine and reducing water loss.
5. Consider the implications of ADH action. By increasing water reabsorption, ADH helps maintain blood volume and pressure, and prevents dehydration, especially in conditions where water intake is limited.