Which hormones primarily regulate the reabsorption of water in the kidneys?

Antidiuretic Hormone (ADH), also known as vasopressin, plays a key role in regulating water reabsorption in the kidneys. It acts primarily on the collecting ducts of the nephron, promoting the insertion of aquaporin-2 channels in the membranes of kidney cells. This action increases the permeability of the collecting ducts to water, allowing more water to be reabsorbed back into the bloodstream and thus concentrating the urine. When the body is dehydrated or when there is an increase in plasma osmolarity, ADH secretion is stimulated, resulting in enhanced water reabsorption.

Aldosterone, another hormone that is involved in water regulation, acts mainly on the distal convoluted tubule and collecting ducts to increase sodium reabsorption. With sodium reabsorption, water follows osmotically, further contributing to water retention. While aldosterone is primarily known for its role in regulating sodium and potassium levels, its actions also significantly influence water reabsorption indirectly.

Together, ADH and aldosterone coordinate the body’s fluid balance by adjusting water reabsorption in response to physiological needs, thereby helping to maintain blood pressure and blood volume. These hormonal actions are critical, especially in maintaining homeostasis in varying hydration states