Which hormone is primarily responsible for regulating water balance in the body?

• A. Insulin
• B. Antidiuretic hormone (ADH)
• C. Estrogen
• D. Glucagon

Answer: (B)

Antidiuretic hormone (ADH), also known as vasopressin, is the hormone primarily responsible for regulating water balance in the body. ADH is produced in the hypothalamus and released from the posterior pituitary gland in response to signals indicating dehydration or increased plasma osmolality. When released, ADH acts on the kidneys to promote the reabsorption of water from the filtrate back into the bloodstream, thereby reducing urine output and conserving water. This critical mechanism helps maintain fluid homeostasis, ensuring that the body retains enough water to function properly without becoming overly diluted or concentrated.

In contrast, other hormones listed play different primary roles: insulin regulates blood glucose levels, estrogen is involved in reproductive processes and secondary sexual characteristics, and glucagon raises blood glucose levels by promoting the release of glucose from the liver. These functions do not primarily pertain to water balance, highlighting the unique and essential role of ADH in maintaining hydration status in the body.