Which hormone is responsible for water reabsorption in the kidneys?

The hormone responsible for water reabsorption in the kidneys is ADH, also known as vasopressin. This hormone is produced in the hypothalamus and released from the posterior pituitary gland. ADH plays a crucial role in regulating the body's osmolarity and maintaining water balance. When the body is dehydrated or when blood osmolarity increases, ADH levels rise, leading to an increase in the permeability of the kidney's collecting ducts to water. This allows more water to be reabsorbed back into the bloodstream, thereby concentrating the urine and reducing water loss from the body.

In contrast, oxytocin is primarily involved in childbirth and lactation, playing no significant role in water reabsorption. Aldosterone, while important for regulating sodium and potassium levels in the kidneys, primarily influences electrolyte balance rather than directly affecting water reabsorption. FSH (Follicle-Stimulating Hormone) is involved in reproductive processes and has no relationship with kidney function or water reabsorption.