What is the function of antidiuretic hormone (ADH)?

Antidiuretic hormone (ADH), also known as vasopressin, plays a critical role in regulating water balance in the body. Its main function is to increase the permeability of the renal tubules, particularly in the collecting ducts of the kidneys. When ADH is released, it binds to receptors on the cells in these tubules, leading to the insertion of aquaporin channels into the cell membranes. These channels facilitate the reabsorption of water back into the bloodstream, thereby concentrating the urine and reducing urine volume.

This mechanism is essential for maintaining proper hydration and blood osmolarity. When the body is dehydrated or when blood volume is low, ADH secretion increases, promoting water retention. Conversely, when the body is well-hydrated, ADH levels decrease, allowing for more urine production and the elimination of excess water.

This understanding highlights the importance of ADH in regulating fluid balance, which is crucial for maintaining homeostasis. The other options do not accurately reflect the primary function of ADH; rather, they pertain to different physiological processes.