The main way the endocrine system affects the excretory system is in controlling the amount of water released with urine. The endocrine system releases a series of hormones to cause the kidneys to resorb water from the urine when blood water levels are low.
The hypothalamus monitors the levels of electrolytes in the blood. An increasing concentration of electrolytes indicates dehydration, while a lower concentration can indicate over-hydration. The most common causes of dehydration are inadequate water intake, excessive perspiration and blood loss. When the hypothalamus detects that the body is dehydrated, it produces antidiuretic hormone that is then transferred to and released by the pituitary gland.
Antidiuretic hormone circulates to the kidneys, where it causes them to increase the rate at which they resorb water. It does this by causing the kidneys to form water channels in the tubules that wind through the kidneys. The water flowing back into the bloodstream causes a reduction in antidiuretic hormone until the channels are closed again.
Another hormone that regulates the way kidneys absorb water is aldosterone, which is produced by the adrenal glands. Aldosterone changes the way the body deals with dissolved chemicals to affect how water is absorbed by the kidneys.