Final answer:
The correct answer to what is predominantly absorbed into circulation after protein digestion is amino acids, dipeptides, and tripeptides, which are broken down in the small intestine and absorbed through active transport.
Step-by-step explanation:
After protein digestion, the predominant product absorbed into circulation are amino acids, dipeptides, and tripeptides. Protein digestion begins in the stomach with enzymes such as pepsin and continues in the small intestine with enzymes like trypsin, chymotrypsin, and various peptidases. These processes break down proteins into smaller peptides and free amino acids. Through active transport mechanisms that are linked to the active transport of sodium, these breakdown products are absorbed primarily in the duodenum and jejunum. Dipeptides and tripeptides are transported actively into the absorptive epithelial cells, where they are further broken down into amino acids before being released into the capillary blood. The correct answer to the question is D. AA, Dipeptides, and Tripeptides.