What hormone is responsible for the reabsorption of water in the kidneys?

The hormone responsible for the reabsorption of water in the kidneys is antidiuretic hormone (ADH), also known as vasopressin. ADH is produced in the hypothalamus and released by the posterior pituitary gland. Its main function is to regulate the body's water balance by increasing the permeability of the collecting ducts in the kidneys. When ADH levels are high, more water is reabsorbed from the filtrate back into the bloodstream, resulting in more concentrated urine and reduced urine volume. This mechanism helps the body conserve water, especially in situations of dehydration or high plasma osmolarity.

The other hormones mentioned have different roles in the body. Adrenocorticotropic hormone (ACTH) primarily stimulates the adrenal glands to release corticosteroids, primarily involved in stress response and metabolism. Thyroxine (T4) is a hormone produced by the thyroid gland that regulates metabolism and energy production. Insulin is crucial for regulating glucose levels in the blood and facilitating its uptake by cells. Each of these hormones plays a significant role in maintaining different homeostatic functions but does not directly influence water reabsorption in the kidneys like ADH does.