What role does ADH play in the body?

ADH, or antidiuretic hormone, primarily functions in regulating water balance in the body. Produced by the hypothalamus and released by the posterior pituitary gland, ADH plays a crucial role in maintaining the body's fluid homeostasis. When the body is dehydrated or when blood osmolarity increases, ADH secretion is stimulated. It acts on the kidneys to promote water reabsorption; specifically, it increases the permeability of the kidney tubules to water, allowing more water to be reabsorbed back into the bloodstream instead of being excreted in urine. This action effectively decreases urine volume and helps retain water, which is vital for maintaining normal blood pressure and overall fluid balance in the body.

The other options pertain to different physiological functions not directly associated with ADH. For example, regulating carbohydrate metabolism relates to hormones like insulin and glucagon, balancing oxygen levels involves respiratory control mechanisms, and stimulating digestion refers to hormones such as gastrin and secretin. Therefore, the role of ADH is specifically tied to its ability to control water balance.