Absorption of large polypeptides, oligopeptides, and free amino acids occurs primarily in which part of the gastrointestinal tract?

Absorption of large polypeptides, oligopeptides, and free amino acids occurs primarily in which part of the gastrointestinal tract?

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

Answer: (B)

The small intestine is the main site because it provides the largest surface area and the right transport mechanisms to move protein-derived nutrients into the bloodstream. Pancreatic proteases and brush-border peptidases break large polypeptides into smaller peptides and amino acids, and the enterocytes lining the villi have specific transporters to take up these units. Di- and tri-peptides are imported by PepT1 and then rapidly hydrolyzed inside the cell, while free amino acids use separate amino acid transporters. This coordinated digestion and absorption system is most active here, so most protein-derived nutrients are absorbed in the small intestine. The stomach mainly aids digestion with acid and enzymes but little absorption, the mouth has negligible absorption, and the large intestine mostly reabsorbs water and electrolytes rather than proteins.

The small intestine is the main site because it provides the largest surface area and the right transport mechanisms to move protein-derived nutrients into the bloodstream. Pancreatic proteases and brush-border peptidases break large polypeptides into smaller peptides and amino acids, and the enterocytes lining the villi have specific transporters to take up these units. Di- and tri-peptides are imported by PepT1 and then rapidly hydrolyzed inside the cell, while free amino acids use separate amino acid transporters. This coordinated digestion and absorption system is most active here, so most protein-derived nutrients are absorbed in the small intestine. The stomach mainly aids digestion with acid and enzymes but little absorption, the mouth has negligible absorption, and the large intestine mostly reabsorbs water and electrolytes rather than proteins.