Osmoregulation
The amount of water reabsorbed is controlled by hormones such as antidiuretic hormone (ADH), aldosterone, and angiotensin II. For example, too high solute concentration in the blood (osmolarity) is detected by osmoreceptors in the hypothalamus (part of the brain). The hypothalamus then stimulates ADH release from the pituitary gland to make the walls of the collecting ducts more permeable to water. Therefore, more water is reabsorbed from fluid in the kidneys to prevent too much water from being excreted.