Gastric activity is controlled in three phases: cephalic, gastric, and intestinal. In the gastric phase, the sight, smell, and taste of food increases gastric secretions to prepare the stomach for incoming food.
In the gastric phase, food in the stomach triggers reflexes to increase its secretions and motility. Gastrin is released into the bloodstream due to distension of the stomach (sensed by stretch receptors) and the presence of foods (sensed by chemoreceptors). Gastrin stimulates cells of the stomach to secrete gastric acid. Activation of the parasympathetic vagus nerve further stimulates gastric motility and secretions.
In the intestinal phase of the control of gastric activity, food in the duodenum shuts down stomach secretions and motility. The presence of lipids and carbohydrates stimulate secretion of CCK (cholecystokinin). Decreased pH in the duodenum stimulates secretin release. Together, CCK and secretin inhibit the secretion of gastric acid.
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