Although single amino acids are liberated in the intestinal contents, there is insufficient power in the digestive enzymes to render all of the amino acids singly for absorption. Thus, the brush border of the absorptive cell absorbs not only the single amino acids but also di- and tripeptides. In the process of absorbing the peptides, the enterocytes hydrolyze them to their amino acid constituents. There is little evidence that peptides enter the blood stream. There are specific transport systems for each group of functionally similar amino acids.