11. A hormone-generating machine.
Eating and digesting your food is most likely something you never have to think about. Yet your GI tract is home to a veritable orchestra of hormones stimulated by epithelial cells that line the stomach and small intestine. These hormones engage in a wide range of functions, including stimulating appetite, encouraging the secretion of enzymes and gastric acid, and reminding the gall bladder to contract and empty. These hormones directly enter the blood and eventually affect the function of other parts of the digestive system, including the liver and pancreas, and even your brain. Gastrin is a hormone that is produced by ‘G’ cells in the lining of the stomach and upper small intestine.
During a meal, gastrin stimulates the stomach to release gastric acid. This allows the stomach to break down proteins swallowed as food and absorb certain vitamins. Ghrelin is produced in the stomach, and its function is to tell the brain that the body has to be fed. It increases appetite. It stimulates the release of gastric juice rich in pepsin and hydrochloric acid. Secretin is a hormone that regulates water homeostasis throughout the body and influences the environment of the duodenum by regulating secretions in the stomach, pancreas, and liver. It is a peptide hormone produced in the S cells of the duodenum, which are located in the intestinal glands. For more info on hormones, see this article.