Vitamin B12 is a cofactor of enzymes which synthesise tetrahydrofolic acid, which, in turn, is needed for the synthesis of DNA components. An impairment of DNA synthesis will affect rapidly dividing cell populations, among them the haematopoietic cells of the bone marrow, which may result in pernicious anemia . This condition may result from a destruction of the gastric mucosa by e.g. autoimmune gastritis or the resection of large parts of the lower ileum, which is the main site of vitamin B12 absorption, or of the stomach. Mucous neck cells are found between the parietal cells in the neck of the gland. Endocrine cells Endocrine cells are scattered, usually solitary, throughout the epithelium of the gastrointestinal tract.
G cells are most frequent in the middle third of the glands.
They stimulate the secretion of acid and pepsinogen. G cell function is stimulated by nervous input, the distension of the stomach or secretagogues. D cells are found mainly in glands of the pyloric antrum. They inhibit G cells and thereby acid production. D cell function is stimulated by acid in the lumen of the stomach and duodenum.