What is the primary role of anti-diuretic hormone (ADH)?

The primary role of anti-diuretic hormone (ADH), also known as vasopressin, is to regulate water balance in the body by promoting water reabsorption in the kidneys. When the body needs to conserve water, ADH is released from the posterior pituitary gland in response to signals indicating dehydration or increased plasma osmolality.

Once ADH reaches the kidneys, it acts on the collecting ducts, increasing their permeability to water. This allows more water to be reabsorbed back into the bloodstream rather than being excreted in urine, leading to more concentrated urine and a decrease in urine volume. This mechanism helps to maintain blood volume and blood pressure and prevents dehydration.

Other options do not accurately represent the primary function of ADH. While the regulation of electrolyte balance and blood pressure may be influenced by fluid balance, they are not the direct roles of ADH. Additionally, ADH does not increase urine production; rather, it decreases urine output by facilitating water reabsorption.