1. protein in food enters the esophagus and stomach through the mouth. Gastric mucosa secretes gastrin, which stimulates gastric cavity wall cells to secrete gastric acid and pepsinogen. Pepsin breaks down protein in food into polypeptide fragments with different sizes. As chyme enters the small intestine, the small intestine stimulates the pancreas to secrete pancreatic juice, and at the same time neutralizes gastric acid, so that the PH value reaches about 7.0. At the same time, the duodenum in the small intestine releases intestinal motilin, which stimulates the pancreas to secrete trypsinogen, chymotrypsin and carboxypeptidase. It can be converted into trypsinogen, which can further decompose the peptide into shorter peptide segments, and finally decompose it into

2, amino acids, and then absorbed by intestinal mucosal epithelial cells into the body.

3. Amino acids are components of protein and play an important role in human nutrition and physiology. People's demand for protein is actually the demand for amino acids.

4. protein, which we ingest from food every day, is finally decomposed into amino acids through the action of enzymes such as pepsin, trypsin, chymotrypsin and carboxypeptidase in the gastrointestinal tract, and then absorbed by intestinal mucosal epithelial cells.