Final answer:
The absorption of amino acids in the small intestinal epithelial cells is primarily through secondary active transport, utilizing specific carrier systems and linked to sodium ion transport. It does not rely on bile or leak channels, and multiple amino acids can be absorbed simultaneously when part of dipeptides or tripeptides.
Step-by-step explanation:
The absorption of amino acids across the apical membrane of a small intestinal epithelial cell mainly happens via secondary active transport. This is a process where the transport of amino acids is coupled with the transport of sodium ions (Na+). Most proteins are absorbed in the form of amino acids or short chains called dipeptides or tripeptides that are actively transported; however, prior to entering the capillary blood, they are broken down into free amino acids through diffusion. The absorption of amino acids is an uphill process and involves specific carrier systems for different amino acids, such as those for neutral, basic, acidic amino acids, and imino acids like proline.
It does not depend on a gradient established by leak channels, nor does it require the solubilization actions of bile, as bile is mainly involved in the emulsification and digestion of dietary fats, not amino acids. Furthermore, amino acids can be absorbed more than one at a time when they are part of dipeptides or tripeptides.