2.2.1.5 Antidiuretic hormone (ADH) increases water absorption in the headers

Anti-diuretic hormone or ADH (also called vasopressin) is secreted from the posterior pituitary gland and increases the water uptake in the renal collecting ducts. It does so by increasing the permeability of the collecting ducts to water. Since the collecting ducts are situated in the renal medulla where there is increasing salt concentration the deeper you go, the increased permeability leads to an increase in the reabsorption of water as the filtrate passes down the collecting ducts. In this way the kidneys are able to produce more concentrated urine and at the same time increase body fluids.