What Hormones are Active in the Digestive Process?

Cholecystokinin

Cholecystokinin (CCK) is found in the duodenal mucosa and is stimulated into action by fatty chyme and partially digested proteins. This hormone targets multiple organ systems, including the stomach, pancreas, gallbladder, and hepatopancreatic sphincter. CCK inhibits gastric secretion, increases pancreatic juice secretion, stimulates gallbladder contraction and bile release, relaxes the hepatopancreatic sphincter, and potentiates secretin's action in the liver and pancreas.

Gastric inhibitory peptide (GIP) or glucose-dependent insulinotrophic peptide

Gastric inhibitory peptide (GIP) is a hormone produced in the duodenal mucosa that is stimulated by fatty chyme. GIP stimulates insulin release in the beta cells of the pancreas, which lowers blood sugar levels. GIP also has a minor effect on inhibiting HCl production in the stomach.

Gastrin

The site of gastrin production is the G cells found in the stomach mucosa. Food, especially partially digested proteins, and acetylcholine, released by nerve fibers, stimulate gastrin production. Gastrin increases stomach acid secretion and contributes to stimulating gastric emptying. In the small and large intestines, gastrin stimulates contraction of intestinal muscle, relaxes the ileocecal valve, and stimulates mass movements of the colon.

Histamine

Histamine is a hormone produced in the stomach lining. It is released in response to the presence of food in the stomach. Histamine stimulates the parietal cells to secrete hydrochloric acid (HCl). The HCl helps break down the food so that it can be absorbed into the bloodstream.

Intestinal gastrin

Gastrin is a hormone produced in the lining of the duodenum, the first part of the small intestine. It is stimulated by acidic and partially digested foods moving through the duodenum. This hormone then stimulates the gastric glands in the stomach to produce gastric juices, and also increases the motility of the stomach. The combined effects of gastrin on gastric juices and motility help to digest food and prepare it for absorption in the small intestine.

Motilin

Found in the duodenal mucosa, motilin is triggered by fasting and is periodically released every 1.5 to 2 hours by neural stimuli. It stimulates the migrating motor complex of the proximal duodenum.

Secretin

Secretin is a hormone produced in the duodenal mucosa. It is released in response to acidic chyme and partially digested proteins and fats in the duodenum. Secretin inhibits gastric gland secretion and gastric motility during the gastric phase of secretion. It also increases the output of pancreatic juice rich in bicarbonate ions, which helps to neutralize the acidic chyme. Secretin also potentiates the action of cholecystokinin (CCK), a hormone that stimulates the gallbladder to contract and release bile into the duodenum. Finally, secretin increases bile output from the liver.

Serotonin

Many people do not realize that serotonin, a neurotransmitter that affects mood, is also released from the lining of the stomach. The presence of food in the stomach stimulates the production of serotonin, which then causes the muscles of the stomach to contract. This contraction helps move food through the digestive tract, and the serotonin released from the stomach lining also helps regulate appetite.

Somatostatin

Somatostatin is a hormone that is released from the stomach and duodenal mucosa. It is triggered by the presence of food in the stomach and by stimulation by sympathetic nerve fibers. Somatostatin inhibits gastric secretion of all products, pancreatic secretion, gastrointestinal blood flow, intestinal absorption, and contraction of bile release. In short, somatostatin is the quick shutdown function of the digestive system used in times of physiological stress.

Vasoactive intestinal peptide (VIP)

The last hormone we will discuss is vasoactive intestinal peptide (VIP). VIP is produced by enteric neurons, which are nerve cells located in the lining of the gastrointestinal tract. VIP is triggered by chyme, which is a mixture of partially digested food and digestive juices. VIP stimulates the secretion of buffers in the small intestines, which help to neutralize stomach acid. VIP also dilates intestinal capillaries, which increases blood flow to the intestines, and relaxes the smooth muscle of the small intestines, which allows food to pass through more easily. In the pancreas, VIP increases the secretion of digestive enzymes. In the stomach, VIP inhibits the secretion of stomach acid.