Secretin is a hormone that regulates water levels in the body by acting on the hypothalamus, pituitary gland and kidneys, and modulates the pH of the duodenum by acting on secretions in the stomach, pancreas and liver. It is produced by the cells of the duodenum. It was the first hormone ever to be identified and was the first to ever be called a "hormone", a term coined by one of its co-discoverers. Simultaneously, secretin opens pathways for water molecules so they can be absorbed into the body from the water content of food, and also triggers the kidneys to increase urination in response.