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Additional recommended knowledge
Parietal cells produce gastric acid (hydrochloric acid) in response to histamine (via H2 receptors), 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+ acts via protein kinases to increase the transport of acid into the stomach.
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.
Hydrochloric acid is formed in the following manner:
The resulting highly-acidic environment causes proteins from food to unfold (or denature), exposing the peptide bonds that link together amino acids. HCl also activates pepsin, allowing it to help digestion by breaking specific peptide bonds, a process known as proteolysis. Furthermore, the sudden increase in gastric acid secretion following a meal can causes a physiological phenomenon called the alkaline tide, which is due to the production and export of bicarbonate from parietal cells.
Parietal cells secrete acid in response to three types of stimuli:
Upon stimulation, adenylate cyclase is activated within the parietal cells. This increases intracellular cyclic AMP, which leads to activation of protein kinase A. Protein kinase A phosphorylates proteins involved in the transport of H+/K+ ATPase from the cytoplasm to the cell membrane. This causes resorption of K+ ions and secretion of H+ ions. The pH of the secreted fluid can fall 'by' 0.8.
Parietal cells also produce intrinsic factor. Intrinsic factor is required for the absorption of vitamin B12 in the diet. Atrophic Gastritis, in particular in the elderly, will cause an inability to absorb B12 and can lead to deficiencies.
Diseases of parietal cells
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Parietal_cell". A list of authors is available in Wikipedia.|