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Intrinsic factor (IF), cobalamin binding intrinsic factor, [5] also known as gastric intrinsic factor (GIF), is a glycoprotein produced by the parietal cells (in humans) or chief cells (in rodents) of the stomach. It is necessary for the absorption of vitamin B 12 later on in the distal ileum of the small intestine. [6]
A canaliculus is an adaptation found on gastric parietal cells. It is a deep infolding, or little channel, which serves to increase the surface area, e.g. for secretion. The parietal cell membrane is dynamic; the numbers of canaliculi rise and fall according to secretory n
Once in the more neutral duodenum, pancreatic enzymes break down the protective glycoprotein. The freed vitamin B12 then binds to intrinsic factor which is then absorbed by the enterocytes in the ileum. The stomach is a distensible organ and can normally expand to hold about one litre of food. [22]
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.
The parietal cells of the human stomach are responsible for producing intrinsic factor, which is necessary for the absorption of vitamin B12. B12 is used in cellular metabolism and is necessary for the production of red blood cells, and the functioning of the nervous system.
Digestion is the breakdown of large insoluble food compounds into small water-soluble components so that they can be absorbed into the blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream .
Another important secretion of the parietal cells is intrinsic factor. Intrinsic factor is a glycoprotein essential for the absorption of vitamin B12. [1] The parietal cells also produce and release bicarbonate ions in response to histamine release from the nearby ECLs, and so serve a crucial role in the pH buffering system. [11]
As a result, the stomach's secretion of essential substances such as hydrochloric acid, pepsin, and intrinsic factor is impaired, leading to digestive problems. The most common are pernicious anemia possibly leading to vitamin B 12 deficiency; and malabsorption of iron, leading to iron deficiency anaemia. [2]