Introduction gastric acid secretion
Gastric acid secretion is produced in different phases. Hydrogen (H+) and chloride (Cl-) ions are produced separately from the cytoplasm of parietal cells and mixed in the canaliculi. Gastric acid is then secreted into the gastric gland lumens and gradually reaches the stomach lumen.
Different phases of gastric acid secretion:
- Cephalic phase- Approximately 30% of gastric secretion.
- Gastric phase- Approximately 60% of gastric secretion.
- Intestinal phase- Approximately 10% of the gastric secretion.
Approximately 30% of gastric secretion occurs in this phase. When it occurs even before food enters the stomach of the body, especially while it is being eaten.
Stimulation of gastric juice secretion in response to smelling and tasting, chewing, swallowing, and conditioned reflexes in anticipation of food. There are 2 mechanisms that promote the secretion of gastric in the cephalic phase.
The first mechanism is the direct stimulation or sensitization of the parietal cell by vagus nerves, which release Ach and the second mechanism is indirect stimulation of the parietal cells by gastrin. In the indirect path, vagus nerves release such as GRP at the G cells, stimulating or promoting gastrin secretion; gastrin enters the circulation and stimulates the parietal cells to secrete HCl.
Approximately 60% of gastric secretion occurs in this phase. When it occurs once food enters the stomach. This phase is stimulated by the distension of the stomach & the presence of breakdown products of protein compounds, amino acids, & small peptides compounds. There are four mechanisms are involved:
The first 2 mechanisms, which are initiated by the stomach distension, are similar to those utilized in the cephalic phase of gastric acid secretion: Distention causes direct vagal stimulation of the parietal cells & indirect stimulation or sensitization of the parietal cells via gastrin release.
The third mechanism is initiated by distension of the stomach antrum and involves local reflexes that stimulate gastrin release and the fourth mechanism is a direct effect of amino acids & small peptides on the G cells to stimulate the release of gastrin.
Account for only 10% of gastric secretion occurs in this phase. The minor role in the stimulation or sensitization of gastric acid secretion. It has a main role in the inhibition of the secretion of gastric acid. In the early intestinal phase, the presence of food in the duodenum of the body causes the secretion of small amounts of gastric juice by the stomach.
Influences on gastric acid secretion are the reflex and hormonal feedback mechanism initiated from the mucosa of the small intestine. Later, the presence of food in the intestine inhibits gastric secretion.