Where does the majority of protein digestion occur after the stomach?

• A. Duodenum
• B. Large intestine
• C. Mouth
• D. Stomach

Answer: (A)

After the stomach, most protein digestion happens in the duodenum, the first part of the small intestine. Here chyme mixes with pancreatic secretions that include proteases such as trypsin, chymotrypsin, and carboxypeptidases, along with brush-border peptidases on the enterocytes. These enzymes break proteins down into small peptides and amino acids that are ready for absorption. The stomach does initiate protein digestion with pepsin, but that alone doesn’t account for the majority, and the large intestine and mouth contribute little to proteolysis. That combination makes the duodenum the main site for completing protein digestion after the stomach.