Define the Absorption of Amino Acid

Proteins are absorbed in the form of amino acids. Amino acid transport occurs 'only in the presence of simultaneous sodium transport. Carrier systems are present in the brush border of the epithelial cells. Amino acids are also transported by sodium gradient mechanism. The carrier has a receptor site for both an amino acid molecule and a sodium ion. Only when both sites are filled, the carrier will move to the interior of the cell. The sodium diffusion to the cell interior pulls the carrier and its attached amino acids to the interior where amino acids are trapped. They diffuse through the sides or base of the cell into the portal blood. There are four different carrier systems - one transports neutral amino acid, second one transports basic amino acid, third transports acidic amino acids and the fourth transports proline and hydroxyproline.