Tuesday 28 June 2005
parietal cell; parietal cells; oxyntic cells
Definition: Parietal cells, or oxyntic cells, are the stomach epithelium cells that secrete gastric acid and intrinsic factor acetylcholine (M3 receptors) and gastrin (CCK2 receptors).
The histamine receptors act by increasing intracellular cAMP, whereas the muscarinic and gastrin receptors increase intracellular Ca2+ levels.
Both cAMP and Ca2+ act via protein kinases to increase the transport of acid into the stomach.
Gastrin is more important indirectly by increasing histamine synthesis in ECL cells, as gastrin has no effect on the maximum histamin-stimulated gastric acid secretion.
Parietal cells contain an extensive secretory network (called canaliculi) from which the HCl is secreted by active transport into the stomach.
The enzyme hydrogen potassium ATPase (H+/K+ ATPase) is unique to the parietal cells and transports the H+ against a concentration gradient of about 3 million to 1, which is the steepest ion gradient formed in the human body.
Parietal cells also produce intrinsic factor. Intrinsic factor is required for the absorption of Vitamin B12 in the diet.
A long-term deficiency in vitamin B12 can lead to megaloblastic anemia, characterized by large fragile erythrocytes.
Pernicious anemia is a condition where intrinsic factor is not produced and leads to the same type of anemia.
Atrophic gastritis, particularly in the elderly, will cause an inability to absorb B12 and can lead to deficiencies such as decreased DNA synthesis and nucleotide metabolism in the bone marrow.
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 membrane of parietal cells is dynamic; the numbers of canaliculi rise and fall according to secretory need.
This is accomplished by the fusion of canalicular precursors, or "tubulovesicles", with the membrane to increase surface area, and the reciprocal endocytosis of the canaliculi (reforming the tubulovesicles) to decrease it.
parietal cell hyperplasia
- gastric cells