Three Phases of Stomach Secretion
Before discussing the three phases of stomach/gastric secretion, it is vital to define stomach secretion. Stomach secretion is the process resulting from eating food, followed by the entry of food in the stomach and small intestine (Walton, 2009). All the three gastric phases can be deduced in the above definition whereby the act of eating food amounts to the cephalic phase, entry of food in the stomach leads to gastric phase and entry of food in the duodenum, the first part of small intestine contributes to intestinal phase. Each phase plays different functions as outlined below:
Cephalic Phase: Cephalic phase is controlled by the brain, and it is initiated by, thought, sight, taste or smell of food. It takes place before the arrival of food in the stomach. Through nerve impulses that originate from cerebral cortex in the brain, the phase stimulates the stomach to secrete gastrin, which in return boosts the release of gastric juice. Gastric juice is responsible for the breaking down of proteins present in the food.
Gastric Phase: Gastric Phase begins immediately upon the entry of food in the stomach. The phases involve the production of three chemicals: gastrin, histamine, and acetylcholine (Ach) all which stimulate stomach walls to increase gastric secretion. It is in this phase where food is formed into chyme before entering the small intestine. Chyme is thick fluid mass, which is halfway digested food.Intestinal Phase: Once the chyme enters the duodenum, small intestine moderates secretion of gastric juice through hormones and nerve impulses. First, the duodenum boosts the secretion of gastric through vagal reflexes that accentuates stomach as well as amino acids and peptides in the chyme to stress duodenum’s G cells to secrete more gastrin, which stimulates the stomach further. However, immediately, the partially digested fats and acid in the duodenum activates inhibitory signals to stop gastric secretion in the stomach.