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Vitamin B 12 is absorbed by a B 12-specific transport proteins or via passive diffusion. [12] Transport-mediated absorption and tissue delivery is a complex process involving three transport proteins: haptocorrin (HC), intrinsic factor (IF) and transcobalamin II (TC2), and respective membrane receptor proteins. HC is present in saliva.
The same cells in the stomach that produce gastric hydrochloric acid, the parietal cells, also produce a molecule called the intrinsic factor (IF), which binds the B 12 after its release from haptocorrin by digestion, and without which only 1% of vitamin B 12 is absorbed. Intrinsic factor (IF) is a glycoprotein, with a molecular weight of 45 kDa.
In pigs it is obtained from the pylorus and beginning of the duodenum; [12] in human beings it is present in the fundus and body of the stomach. [ 13 ] The limited amount of normal human gastric intrinsic factor limits normal efficient absorption of B 12 to about 2 μg per meal, a nominally adequate intake of B 12 .
Transcobalamin I (TC-1), also known as haptocorrin (HC), R-factor, and R-protein is encoded in the human by the TCN1 gene. TC-1 is a glycoprotein produced by the salivary glands of the mouth. It primarily serves to protect cobalamin (Vitamin B12) from acid degradation in the stomach by producing a HC-Vitamin B 12 complex.
One of the superpowers of vitamin B12 is that it is the only water-soluble vitamin that can be stored in the human body, Kitchens points out, and it can remain stored in the liver for several years.
A prescription form of vitamin B12 can be given as an injection, notes the NIH—typically for people with deficiencies who also have problems absorbing vitamin B12 as well as those who have ...
Its main function is to absorb vitamin B 12, bile salts, and whatever products of digestion that were not absorbed by the jejunum. The ileum follows the duodenum and jejunum and is separated from the cecum by the ileocecal valve (ICV). In humans, the ileum is about 2–4 m long, and the pH is usually between 7 and 8 (neutral or slightly basic).
Downing Street and the Foreign Office are preparing to offer the incoming U.S. president an invitation once he is back in the White House, the report said, without citing specific sourcing. The ...