What does ADH do and how does it work?

Anti-diuretic hormone (ADH) is a hormone produced to help maintain the amount of water in the body when it is dehydrated. Water passes into the Bowman's capsule from the blood in the glomerulus in the nephrons of the kidney. The majority of water in the filtrate is reabsorbed in the proximal convoluted tubule and the Loop of Henle but some naturally remains. ADH causes the remaining water to be reabsorbed by the collecting duct (and also by the distal convoluted tubule but less so) before it is excreted from the body in the urine. ADH is produced by the hypothalamus in the brain and is secreted into the blood by the posterior pituitary gland. It travels in the blood to the kidney. In the kidney ADH binds to specific receptors on the collecting duct and distal convoluted tubule. This causes the enzyme adenyl cyclase to convert ATP to cyclic AMP (two phosphates are removed). Cyclic AMP causes vesicles containing aquaporins (a type of channel protein) to move towards and fuse with the membranes of distal convoluted tubule and collecting duct cells. Water can then move into cells through the aquaporins by osmosis. It can then pass into the capillaries by osmosis. This results in more water remaining in the blood and less being excreted in the urine.