The absorption of amino acids is active. At present, three main special delivery systems for transporting amino acids have been identified on the small intestine wall, which rotate neutral, acidic or basic amino acids respectively. Generally speaking, neutral amino acids are transported faster than acidic or basic amino acids. Similar to the absorption of monosaccharides, the absorption of amino acids is accompanied by the absorption of sodium. When sodium pump activity is blocked, amino acid transport cannot be carried out. The pathway of amino acid absorption is almost completely through the blood. When protein was absorbed by small intestine, the amino acid content in portal vein blood immediately increased.
It was once thought that protein could only be absorbed by hydrolysis into ammonia. However, in recent years, experiments have shown that there are still dipeptide and tripeptide transport systems at the edge of small intestine striations, so many dipeptides and tripeptides can also be completely absorbed by small intestinal epithelial cells, and the absorption efficiency of peptide transport systems may be higher than that of amino acids. Dipeptides and tripeptides entering cells can be further decomposed into amino acids by dipeptidases and tripeptidases in cells, and then enter the blood circulation.
Can intact protein be absorbed by human intestinal epithelial cells? Many experiments have proved that a small amount of food protein can completely enter the blood, because the absorbed amount is small, which is meaningless from the nutritional point of view; On the contrary, they can often be used as antigens to cause allergic reactions or toxic reactions, which are not good for the human body.