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Parietal cells, or oxyntic cells, are the stomach epithelium cells that secrete gastric acid and intrinsic factor.

Contents 1 Acid production 2 Intrinsic factor 3 Diseases of parietal cells 4 See also 5 References 6 External links

[edit] Acid production

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⁺ act 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, which is the steepest ion gradient formed in the human body.

Hydrochloric acid is formed in the following manner:

• Hydrogen ions are formed from the dissociation of water molecules. The enzyme carbonic anhydrase converts one molecule of carbon dioxide and two molecules of water indirectly into a bicarbonate ion (HCO₃^-) and a hydrogen ion (H⁺).
• The bicarbonate ion (HCO₃^-) is exchanged for a chloride ion (Cl^-) on the basal side of the cell and the bicarbonate diffuses into the venous blood leading to an alkaline tide.
• Potassium (K⁺) and chloride (Cl^-) ions diffuse into the canaliculi.
• Hydrogen ions are pumped out of the cell into the canaliculi in exchange for potassium ions, via the H⁺/K⁺ ATPase.

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 pepsinogen, an endopeptidase, 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 cause a physiological phenomenon called an alkaline tide, which is due to the production and export of bicarbonate from parietal cells. The alkaline tide is neutralized by the action of the pancreatic duct which produces a bicarbonate secretion that is deposited into the lumen of the duct while the byproduct, hydrogen ions, are pumped out the basal membrane into the portal blood stream, thereby neutralizing the bicarbonate from the stomach.

Parietal cells secrete acid in response to three types of stimuli:

• H₂ histamine receptors (most significant contribution)
• parasympathetic activity via the Vagus nerve and enteric nervous system
• gastrin (least significant contribution, but note that histamine secretion by ECL cells is due in part to gastrin)

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.

[edit] Intrinsic factor

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 such as decreased DNA synthesis and nucleotide metabolism in the bone marrow.

[edit] Diseases of parietal cells

• Peptic ulcers can result from over-acidity in the stomach. Antacids can be used to enhance the natural tolerance of the gastric lining. Antimuscarinic drugs such as pirenzepine or H₂ antihistamines can reduce acid secretion. Proton pump inhibitors are more potent at reducing gastric acid production since that is the final common pathway of all stimulation of acid production.

• In pernicious anemia, autoantibodies directed against parietal cells or intrinsic factor cause a reduction in vitamin B12 absorption. It can be treated with injections of replacement vitamin B12 (hydroxocobalamin or cyanocobalamin).

• Achlorhydria is another autoimmune disease of the parietal cells. The damaged parietal cells are unable to produce the required amount of gastric acid. This leads to an increase in gastric pH, impaired digestion of food and increased risk of gastroenteritis.

[edit] See also

• Chief cell

[edit] References

• Ganong, William F. (2001). Review of Medical Physiology (20 ed.). New York: McGraw-Hill. pp. 467–70. ISBN 0-07-112064-5. 

[edit] External links

• Illustration of Chief cells and Parietal cells at anatomyatlases.org
• The Parietal Cell: Mechanism of Acid Secretion at vivo.colostate.edu
• Histology at BU 11303loa - Digestive System: Alimentary Canal: fundic stomach, gastric glands, lumen"
• MeSH Gastric+Parietal+Cells
• Physiology at MCG 6/6ch4/s6ch4_8
• Physiology at MCG 6/6ch4/s6ch4_14
• Parietal cell antibody
• Antibody to GPC

v • d • e Digestive system, physiology: gastrointestinal physiology GI tract Upper GI Exocrine Chief cells (Pepsinogen) · Parietal cells (Gastric acid, Intrinsic factor) · Goblet cells (Mucus) Processes Swallowing · Vomiting Fluids Saliva · Gastric juice Lower GI Enteric nervous system Meissner's plexus · Auerbach's plexus Endocrine/paracrine G cells (gastrin) · D cells (somatostatin) · ECL cells (Histamine) enterogastrone: I cells (CCK) · K cells (GIP) · S cells (secretin) Enteroendocrine cells · Enterochromaffin cell · APUD cell Border Brunner's glands · Paneth cells · Enterocytes Fluids Intestinal juice Processes Segmentation contractions · Migrating motor complex · Borborygmus · Defecation Either/both Processes Peristalsis (Interstitial cell of Cajal) · Gastrocolic reflex · Digestion Accessory Fluids Bile · Pancreatic juice Processes Enterohepatic circulation Abdominopelvic Peritoneal fluid digestive system navs: anat of tract,glands,perit,diaphragm/physio/dev, noncongen/congen/congen of d+w/neoplasia, symptoms+signs/eponymous, proc

v • d • e Human cell types Blood/immune lymphoid: B cell  · T cell (Cytotoxic T cell, Natural Killer T cell, Regulatory T cell, T helper cell) · Natural killer cell myeloid: granulocytes (Basophil granulocyte, Eosinophil granulocyte, Neutrophil granulocyte/Hypersegmented neutrophil)  · Monocyte/Macrophage  · Red blood cell (Reticulocyte)  · Mast cell  · Thrombocyte/Megakaryocyte  · Dendritic cell Endocrine system thyroid (Thyroid epithelial cell, Parafollicular cell)  · parathyroid (Parathyroid chief cell, Oxyphil cell)  · adrenal (Chromaffin cell) · pineal (Pinealocyte) Nervous system glial cells: Glioblast (Astrocyte, Oligodendrocyte) · Microglia Magnocellular neurosecretory cell  · Stellate cell · Boettcher cell pituitary (Gonadotrope, Corticotrope, Thyrotrope, Somatotrope, Lactotroph ) Respiratory system Pneumocyte (Type I pneumocyte, Type II pneumocyte) · Clara cell · Goblet cell · Alveolar macrophage Circulatory system Myocardiocyte · Pericyte Digestive system stomach (Gastric chief cell, Parietal cell) · Goblet cell · Paneth cell G cells · D cells · ECL cells · I cells  · K cells  · S cells Enteroendocrine cells · Enterochromaffin cell · APUD cell liver (Hepatocyte, Kupffer cell) Cartilage/bone/ muscle/ integumentary system bone: Osteoblast · Osteocyte · Osteoclast · teeth (Cementoblast, Ameloblast) cartilage: Chondroblast · Chondrocyte skin/hair: Trichocyte · Keratinocyte  · Melanocyte (Nevus cell) muscle: Myocyte other: Adipocyte  · Fibroblast (corneal keratocyte) · Tendon cell Urinary system Podocyte  · Juxtaglomerular cell  · Intraglomerular mesangial cell/Extraglomerular mesangial cell  · Kidney proximal tubule brush border cell  · Macula densa cell Reproductive system male (Spermatozoon, Sertoli cell, Leydig cell)  · female (Ovum) see also list of distinct cell types in the adult human body  · -cyte