Cephalic Phase of Digestion

Digestion has three overlapping phases — cephalic, gastric, and intestinal — based on the location of their control center.

The cephalic phase begins before food enters the stomach and is controlled by the central nervous system.

Food-related sensory stimuli, including sight and smell, can initiate the cephalic phase.

Additionally, the taste receptors intensify the signals to the brain while eating.

From the cerebral cortex, these stimuli are relayed to the hypothalamus and the medulla.

The neural output is transmitted via the parasympathetic fibers of the vagus nerve, stimulating the mucous, chief, parietal, and G cells in the stomach.

The G cells of gastric glands secrete gastrin, which stimulates the chief cells to release pepsinogen and the parietal cells to release gastric acid.

The mucus from the mucous cells, combined with the secretions of the parietal and the chief cells, forms gastric juice.

Upon entering the stomach, food triggers the stretch receptors in the wall, activating the long reflexes to the medulla.

In turn, the medulla stimulates increased production of gastric juice via the vagus nerve for a few minutes.