Which brain region releases AVP in response to concentrated blood?

• A. Hypothalamus
• B. Cerebellum
• C. Medulla
• D. Pons

Answer: (A)

Concentrated blood raises plasma osmolality, and the body responds by releasing AVP to conserve water. Osmoreceptors in the hypothalamus detect this change and stimulate magnocellular neurons to synthesize AVP. This hormone is then released from the posterior pituitary into the bloodstream, where it acts on the kidneys to increase water reabsorption in the collecting ducts via V2 receptors, producing more concentrated urine and restoring fluid balance. The cerebellum, medulla, and pons don’t regulate AVP release in response to osmolality, so they aren’t the source of this hormone’s release.