Which hormone is primarily responsible for regulating sodium and water balance?

Aldosterone is the hormone primarily responsible for regulating sodium and water balance in the body. It is produced by the adrenal glands and plays a crucial role in the renin-angiotensin-aldosterone system (RAAS), which is a key regulator of blood pressure and fluid balance.

When blood sodium levels are low or when blood volume decreases, aldosterone secretion increases. This hormone promotes the reabsorption of sodium from the renal tubules back into the bloodstream and enhances the excretion of potassium. The reabsorption of sodium is directly linked to water retention since water follows sodium osmotically. Consequently, by increasing sodium reabsorption, aldosterone helps to maintain blood pressure and fluid equilibrium.

Other hormones mentioned play different roles in the body. Thyroxine, produced by the thyroid gland, primarily regulates metabolism. Insulin, secreted by the pancreas, mainly controls glucose levels in the blood. Cortisol, a steroid hormone released by the adrenal cortex in response to stress, has a broader range of effects, including involvement in glucose metabolism and anti-inflammatory actions, but it does not directly regulate sodium and water balance to the extent that aldosterone does. Thus, aldosterone is the key hormone in this context.