Which hormone facilitates the reabsorption of water in the kidneys?

Vasopressin, also known as antidiuretic hormone (ADH), plays a critical role in the regulation of water balance in the body by promoting the reabsorption of water in the kidneys. It is produced in the hypothalamus and released by the posterior pituitary gland in response to increased plasma osmolality or decreased blood volume. When ADH is secreted, it acts on the collecting ducts of the kidneys, stimulating the insertion of aquaporin-2 channels into the membrane of the kidney tubule cells. This mechanism increases the permeability of these segments to water, allowing more water to be reabsorbed back into the bloodstream. As a result, the body can conserve water, leading to more concentrated urine and helping to maintain proper hydration and osmotic balance.

Other hormones listed do have important functions but do not directly facilitate water reabsorption in the same manner as vasopressin. For instance, aldosterone primarily regulates sodium and potassium balance, adrenaline (epinephrine) is involved in the "fight or flight" response, and cortisol is a glucocorticoid involved in metabolism and the stress response, but not specifically in water reabsorption.