How does dehydration affect ADH release and urine concentration?

How does dehydration affect ADH release and urine concentration?

• A. Dehydration increases ADH release from the pituitary, leading to greater water reabsorption in kidneys and more concentrated urine.
• B. Dehydration decreases ADH release; urine becomes dilute.
• C. Dehydration has no effect on ADH.
• D. Dehydration increases ADH release but reduces urine concentration.

Answer: (A)

When dehydrated, the blood becomes more concentrated, which is detected by osmoreceptors in the hypothalamus. This triggers the posterior pituitary to release antidiuretic hormone (ADH). ADH increases the permeability of the kidney’s collecting ducts to water by promoting more aquaporin channels, so more water is reabsorbed back into the bloodstream. The result is less water lost in urine and urine that is more concentrated (higher osmolality). The other options don’t fit because dehydration does not lower ADH or make urine dilute, and increased ADH would not lead to reduced urine concentration.

When dehydrated, the blood becomes more concentrated, which is detected by osmoreceptors in the hypothalamus. This triggers the posterior pituitary to release antidiuretic hormone (ADH). ADH increases the permeability of the kidney’s collecting ducts to water by promoting more aquaporin channels, so more water is reabsorbed back into the bloodstream. The result is less water lost in urine and urine that is more concentrated (higher osmolality). The other options don’t fit because dehydration does not lower ADH or make urine dilute, and increased ADH would not lead to reduced urine concentration.