Which hormone increases water retention in the kidneys?

Antidiuretic hormone (ADH), also known as vasopressin, plays a crucial role in regulating water balance in the body by promoting water retention in the kidneys. When released from the posterior pituitary gland, ADH acts on the kidneys to increase the permeability of the collecting ducts, allowing more water to be reabsorbed back into the bloodstream rather than being excreted in urine. This process helps to concentrate the urine and maintain overall fluid balance, especially in situations where the body is dehydrated or experiencing low blood volume.

By enhancing water reabsorption, ADH contributes to the regulation of blood pressure and overall hydration status, making it essential for homeostasis. It is particularly important in conditions of high osmolarity of the blood, signaling the kidneys to retain as much water as possible to dilute the plasma and restore balance. This physiological mechanism illustrates the critical function of ADH in renal water conservation.