Intestinal Phase of Digestion

After the gastric phase, the chyme from the stomach moves into the small intestine, gradually decreasing the stomach distention.

In contrast, the arrival of chyme expands the duodenal end of the small intestine, stimulating the local stretch receptors and chemoreceptors to trigger the enterogastric reflex.

This reflex inhibits stimulation of the stomach via the submucosal and myenteric plexuses, as well as parasympathetic stimulation via the medulla.

As a result, both gastrin production and gastric contractions are inhibited.

Additionally, the pyloric sphincter contracts, preventing further discharge of chyme from the stomach to the small intestine.

The incoming chyme stimulates the enteroendocrine cells scattered in the duodenal mucosa to release enterogastrone, such as cholecystokinin or CCK, secretin, and gastric inhibitory peptide or GIP.

Lipids and carbohydrates in the chyme stimulate the release of CCK and GIP. These hormones inhibit gastric secretions and trigger the pancreas to release digestive enzymes and the gallbladder to release bile.

Acidic chyme stimulates the release of secretin. This in turn, stimulates the release of pancreatic juice to increase the pH of chyme, which is favorable for digestion.