Which hormone is primarily involved in regulating the body's water balance?

Antidiuretic hormone (ADH), also known as vasopressin, plays a crucial role in regulating the body's water balance. It is produced in the hypothalamus and released from the posterior pituitary gland in response to high blood osmolality (high concentration of solutes in the blood) or low blood volume.

When released into the bloodstream, ADH acts primarily on the kidneys, promoting the reabsorption of water in the collecting ducts. This process decreases urine output and helps to retain water in the body, thereby concentrating the urine and correcting dehydration. By facilitating this water retention, ADH helps maintain homeostasis, ensuring that body fluids are balanced appropriately in response to various physiological demands.

The other hormones mentioned have different primary functions: Aldosterone regulates sodium and potassium levels and influences blood pressure; Insulin is key for glucose metabolism; Cortisol, a stress hormone, affects various metabolic processes, including glucose and protein metabolism. Hence, their involvement in water balance is not direct or primary as it is with ADH.