Digestion 0.5% hydrochloric acid (HCl), which lowers the pH to the desired pH of 1-3. Acid release is also triggered by acetylcholine and histamine. The intestinal phase has two 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. Protein digestion occurs in the stomach and duodenum in which 3 main enzymes, pepsin secreted by the stomach and trypsin and chymotrypsin secreted by the pancreas, break down food
Stomach the stomach through its lining. This includes: The parietal cells of the human stomach are responsible for producing intrinsic factor, which is necessary for the absorption of vitamin B12. B12 is used in cellular metabolism and is necessary for the production of red blood cells, and the functioning of the nervous system. The movement and the flow of chemicals into the stomach are controlled by both the autonomic nervous system and by the various digestive hormones of the digestive system: Other than gastrin, these hormones all act to turn off the stomach action. This is in response to food products