Hormonal Regulation

Digestion is regulated by the neuroendocrine system, which includes both neural and hormonal mechanisms. In response to food, cells throughout the digestive tract release hormones that regulate digestive secretions and motility.

In the stomach, during the gastric phase, proteins in food trigger the release of gastrin. Gastrin stimulates the release of histamine, a signaling molecule.

Both gastrin and histamine stimulate the production of hydrochloric acid and increase gastric juice secretion, which helps break down food into chyme.

When chyme enters the duodenum, the small intestine releases hormones that slow stomach activity and control the movement of chyme through the rest of the digestive tract.

Two of these hormones, gastric inhibitory peptide, or GIP, and cholecystokinin, or CCK, are released when chyme with high glucose and fats enters the small intestine.

GIP signals the pancreas to release insulin. CCK signals the pancreas to release digestive enzymes and the gallbladder to release bile. Bile helps break down fats.

Another hormone, secretin, is released in the presence of acidic chyme. It stimulates the release of bicarbonate from the pancreas to neutralize the acidity of the chyme and protect the lining of the small intestine.

Lastly, peptide YY is a hormone released by the ileum, the end of the small intestine, and the colon. It slows gastric emptying and intestinal motility so that water and electrolytes are readily absorbed. Peptide YY is also an “I'm full” signal sent to the brain and helps stop eating.