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 food, or no pre-digestion with gastric juices, or both. The gastric lining is usually divided into two regions, an anterior portion lined by fundic glands, and a posterior with pyloric glands. Cardiac glands are unique to mammals, and even then are absent in a number of species. The distributions of these glands vary between species, and do not always correspond with the same regions as in humans. Furthermore, in many non-human mammals, a portion of the stomach anterior to the cardiac glands is lined with epithelium essentially identical to that of the oesophagus. Ruminants, in particular, have a complex stomach,