Which hormone is involved in the regulation of water balance in the body?

The hormone that plays a critical role in the regulation of water balance in the body is Antidiuretic hormone (ADH), also known as vasopressin. This hormone is produced in the hypothalamus and stored in the posterior pituitary gland. Its primary function is to promote water reabsorption in the kidneys, specifically in the collecting ducts. When the body is dehydrated or when blood osmolarity increases, ADH is released into the bloodstream, prompting the kidneys to retain more water. This process helps to concentrate urine and reduce water loss, thereby assisting in the maintenance of fluid balance and blood pressure.

The other hormones listed do not primarily regulate water balance. Oxytocin is involved in various functions, including childbirth and lactation. Prolactin mainly regulates milk production in the mammary glands. Cortisol, while it has a role in fluid balance and metabolism, is primarily a stress hormone that affects glucose metabolism and immune response rather than directly regulating water retention like ADH does. Therefore, ADH is correctly identified as the key hormone responsible for maintaining water equilibrium in the body.