Gastric Phase of Digestion

Local, neural and hormonal mechanisms trigger the gastric phase after food enters the stomach, lasting approximately 3-4 hours.

The incoming food bolus distends the stomach and triggers the stretch receptors, activating the local short reflexes mediated through the submucosal and myenteric plexuses.

As a result, the secretory activity of the gastric cells is activated, and the muscularis externa produces powerful contractions called mixing waves.

In addition, chemical stimuli like changes in pH and partially digested food also stimulate the release of hormones.

Gastrin secreted by the G cells, stimulate the enterochromaffin-like cells to release histamine, which activates the parietal cells to secrete hydrochloric acid. Additionally gastrin induces the chief cells to release pepsinogen.

This mixture of hydrochloric acid, pepsinogen, and mucus, secreted by the stomach lining, constitutes the gastric juice.

Hydrochloric acid destroys bacteria and partially denatures proteins. It also converts pepsinogen into pepsin, which breaks down proteins into smaller peptides.

Gastric juice and mixing waves further disintegrate food and form chyme.