Final answer:
Proteins are primarily digested in the stomach and small intestine through the action of enzymes like pepsin, trypsin, and chymotrypsin. The secretions for protein digestion, such as pepsin, trypsin, aminopeptidase, and dipeptidase, are stimulated to be released through hormonal control.
Step-by-step explanation:
The digestion of proteins primarily occurs in the stomach and small intestine. In the stomach, the enzyme pepsin, along with hydrochloric acid, breaks down proteins into smaller polypeptides. In the small intestine, pancreatic enzymes such as trypsin and chymotrypsin, as well as brush border enzymes like aminopeptidase and dipeptidase, further break down the polypeptides into amino acids.
The substances secreted for protein digestion are pepsin, trypsin, chymotrypsin, aminopeptidase, and dipeptidase. These secretions are stimulated to be released through hormonal control. When proteins enter the stomach, gastric cells secrete gastrin, which stimulates the release of pepsinogen and hydrochloric acid. In the small intestine, the presence of partially digested proteins triggers the release of secretin and cholecystokinin (CCK), which stimulate the release of pancreatic enzymes and brush border enzymes.