What is the role of antidiuretic hormone (ADH)?

The role of antidiuretic hormone (ADH), also known as vasopressin, is primarily to regulate the body's water balance by increasing water reabsorption in the kidneys. When released from the posterior pituitary gland, ADH acts on the kidney's collecting ducts, making them more permeable to water. This increased permeability allows more water to be reabsorbed back into the bloodstream, effectively concentrating the urine and reducing water loss. This mechanism is vital for maintaining hydration, especially in situations where the body is dehydrated or needs to conserve water, such as during high salt intake or excessive sweating.

ADH's function is crucial for homeostasis—the process by which the body maintains a stable internal environment. This hormone plays a significant role in preventing dehydration and managing blood pressure by influencing the volume of the blood. Conditions that lead to an increase in ADH secretion can improve water retention, thereby affecting the body’s fluid balance directly.

In contrast, other options reflect different physiological actions: metabolic rate and thyroid function are related to other hormones, while milk production is primarily affected by prolactin. Thus, the specific function of ADH focuses on kidney function and fluid balance.