What is the action of antidiuretic hormone (ADH) in the body?

Antidiuretic hormone (ADH), also known as vasopressin, primarily acts on the kidneys to promote the reabsorption of water. It is secreted by the posterior pituitary gland in response to high plasma osmolality or low blood volume. When ADH is released into the bloodstream, it binds to receptors in the collecting ducts of the kidneys, leading to the insertion of aquaporin channels into the membranes of kidney tubule cells. This insertion allows for increased permeability to water, resulting in greater water reabsorption back into the bloodstream.

As a consequence, this mechanism helps to concentrate the urine and decrease water loss from the body, thus playing a crucial role in maintaining fluid balance and proper blood pressure. This action directly counters dehydration, enabling the body to conserve water effectively. Therefore, the correct choice highlights the essential role of ADH in regulating water reabsorption in the renal system.