Science Biojournal- Entry 12

Stage one: Phases of Gastric Secretion
For this process, it can be divided into three phases: Cephalic phase, Gastric phase and intestinal phase.

First up is the Cephalic phase - This phase occurs before food enters the stomach and involves preparation of the body for eating and digestion. Sight and thought stimulate the cerebral cortex. Taste and smell stimulus is sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine. Gastric secretion at this phase rises to 40% of maximum rate. Acidity in the stomach is not buffered by food at this point

The second phase is the Gastric phase - This phase takes 3 to 4 hours. It is stimulated by distention of the stomach, presence of food in stomach and increase in pH. Distention activates long and myentric reflexes. This activates the release of acetylcholine which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach to around pH 6.

Finally, the Intestinal phase - This phase has 2 parts, the excitatory and the inhibitory. Partially-digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibers causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes.

Through these three phases of gastric secretion,it makes up the first part of food digestion.