Where do amino acids enter and exit intestinal epithelial cells?

Where do amino acids enter and exit intestinal epithelial cells?

• A. Amino acids enter via multiple sodium-dependent and independent transporters on the apical membrane and exit via basolateral transporters.
• B. Amino acids are absorbed via diffusion across the brush border.
• C. Amino acids are absorbed via vesicular transport only.
• D. Amino acids are absorbed in the colon.

Answer: (A)

Amino acids cross the intestinal lining through a polarized, transporter‑driven process. At the surface facing the lumen (apical membrane), they are taken into enterocytes by multiple transporters, some sodium‑dependent and others sodium‑independent. The sodium gradient that powers many of these uptake processes is maintained by the Na+/K+ ATPase on the basolateral side, providing the energy for apical uptake. Once inside, amino acids exit across the basolateral membrane into the interstitial fluid and into the portal circulation via dedicated basolateral transporters. This pathway is the primary route for small intestine absorption; diffusion across the brush border is not the main mechanism, and the colon is not the primary site of amino acid absorption.

Amino acids cross the intestinal lining through a polarized, transporter‑driven process. At the surface facing the lumen (apical membrane), they are taken into enterocytes by multiple transporters, some sodium‑dependent and others sodium‑independent. The sodium gradient that powers many of these uptake processes is maintained by the Na+/K+ ATPase on the basolateral side, providing the energy for apical uptake. Once inside, amino acids exit across the basolateral membrane into the interstitial fluid and into the portal circulation via dedicated basolateral transporters. This pathway is the primary route for small intestine absorption; diffusion across the brush border is not the main mechanism, and the colon is not the primary site of amino acid absorption.