Gastric secretion means secretion of digestive juice by the stomach, there are three phases of gastric secretion - Cephalic, Gastric and Intestinal phase.
Three Phases of gastric secretion
Regulation of secretion of the stomach is of three phases they are: Cephalic phase, Gastric phase and Intestinal phase.
Cephalic phase
This gastric secretion phase happens just before food enters the stomach, and this phase prepares the body for eating and digestion.
- In the cephalic phase, the taste or smell of food, food sensation in the mouth, or thought of food generates and sends nervous signals to the hypothalamus and medulla oblongata.
- This signal causes parasympathetic neurons through the vagus nerves to stimulate hydrochloric acid and pepsin secretion in the stomach.
- The parasympathetic stimulation also secretes gastrin by the stomach.
- This hormone taken through the bloodstream and stimulates the secretion of hydrochloric acid and pepsin.
The stomach acidity is not buffered at this stage by the food thus inhibits parietal (acid secretion) and G cell (gastrin secretion) activity through D cell secretion (somatostatin).
Gastric Phase
This phase takes about three to four hours.
- In gastric phase, food has entered and distended the stomach.
- This distention stimulates a parasympathetic reflex through medulla oblongata, and it directly stimulates the gastric glands and releases more gastric juices.
- If protein is available in the stomach, it binds with hydrogen ions and raises the stomach pH. It, furthermore, lifts the inhibition of gastrin and gastric acid secretion.
- This stimulates G cells to release gastrin, which stimulates parietal cells to secrete gastric acid. This causes a continued secretion of hcl (hydrochloric acid) and pepsin, which lowers the pH to one to three (acidic).
Intestinal Phase
Partially digested food fills the duodenum. This phase has two parts, the excitatory, and the inhibitory.
- In the intestinal phase, chyme has entered the duodenum.
- If the chyme has lipids (digested fat) or has pH below two, gastric secretion is inhibited.
- The lipids and acidic pH (hydrogen ions) inhibits gastric secretion by three stages:
- o firstly, signals medulla oblongata to inhibit stimulation of the gastric glands.
- o Secondly local reflexes through neurons in the gut wall to decrease gastric secretion.
- o thirdly releases three local hormones that pass through the circulation to the gastric glands to inhibit its secretion.