Parietal cell

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Parietal cell

Parietal cells, or oxyntic cells, are the stomach

Stomach

In most mammals, the stomach is a hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication....
epithelium

Epithelium

In biology and medicine, epithelium is a Biological tissue composed of cell s that line the cavities and surfaces of structures throughout the body....
cell

Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
s that secrete gastric acid

Gastric acid

Gastric acid is one of the main secretions of the stomach, together with several enzymes and intrinsic factor. Chemically it is an acid solution with a pH of 1 to 2 in the stomach lumen , consisting mainly of hydrochloric acid , and large quantities of potassium chloride and sodium chloride ....
and intrinsic factor

Intrinsic factor

Intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the terminal ileum....
.

etal cells produce gastric acid

Gastric acid

Hydrochloric acid

Hydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong acid mineral acid and has major industrial uses....
) in response to histamine

Histamine

Histamine is a biogenic amine involved in local immune system as well as regulating physiological function in the gut and acting as a neurotransmitter....
(via H₂ receptor

Receptor (biochemistry)

In biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling molecule may attach....
s), acetylcholine

Acetylcholine

The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including homo sapiens....
(M₃

Muscarinic acetylcholine receptor M3

The muscarinic acetylcholine receptor M3, also known as the cholinergic receptor, muscarinic 3, is a muscarinic acetylcholine receptor....
receptors) and gastrin

Gastrin

In humans, gastrin is a hormone that stimulates secretion of gastric acid by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the stomach, duodenum, and the pancreas....
(CCK2 receptor

Cholecystokinin B receptor

The Cholecystokinin B receptor is a human protein that is also known as CCKBR or CCK2, with CCK2 now being the IUPHAR-recommended name....
s).

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Acid production

Parietal cells produce gastric acid

Gastric acid

Hydrochloric acid

Hydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong acid mineral acid and has major industrial uses....
) in response to histamine

Histamine

Histamine is a biogenic amine involved in local immune system as well as regulating physiological function in the gut and acting as a neurotransmitter....
(via H₂ receptor

Receptor (biochemistry)

In biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling molecule may attach....
s), acetylcholine

Acetylcholine

The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including homo sapiens....
(M₃

Muscarinic acetylcholine receptor M3

The muscarinic acetylcholine receptor M3, also known as the cholinergic receptor, muscarinic 3, is a muscarinic acetylcholine receptor....
receptors) and gastrin

Gastrin

Cholecystokinin B receptor

The Cholecystokinin B receptor is a human protein that is also known as CCKBR or CCK2, with CCK2 now being the IUPHAR-recommended name....
s). The histamine receptors act by increasing intracellular cAMP

CAMP

CAMP may stand for:* Cyclic adenosine monophosphate * Cathelicidin* Campaign Against Marijuana Planting* Central Atlantic Magmatic Province...
, 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

Canaliculus (parietal cell)

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....
) from which the HCl is secreted by active transport

Active transport

Active transport is the mediated process of moving particles across a biological membrane against a Concentration_gradient#In_biology . If the process uses chemical energy, such as from adenosine triphosphate , it is termed primary active transport....
into the stomach. The enzyme hydrogen potassium ATPase

Hydrogen potassium ATPase

Gastric hydrogen potassium ATPase is also known as H+/K+ ATPase...
(H⁺/K⁺ ATPase) is unique to the parietal cells and transports the H⁺ against a concentration

Concentration

In chemistry, concentration is the measure of how much of a given chemical substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent....
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
Enzyme

Enzymes are biomolecules that catalysis chemical reactions. Almost all enzymes are proteins. In enzymatic reactions, the molecules at the beginning of the process are called Substrate , and the enzyme converts them into different molecules, the products....
carbonic anhydrase
Carbonic anhydrase

The carbonic anhydrases form a family of enzymes that catalyst the rapid conversion of carbon dioxide to bicarbonate and Hydronium ions, a reaction that occurs rather slowly in the absence of a catalyst....
converts one molecule of carbon dioxide
Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
and one molecule of water indirectly into a bicarbonate
Bicarbonate

In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid. Its chemical formula is HCO3−....
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
Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
(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
Hydrogen potassium ATPase

Gastric hydrogen potassium ATPase is also known as H+/K+ ATPase...
.

The resulting highly-acidic environment causes protein

Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
s from food to unfold (or denature

Denaturation (biochemistry)

Denaturation is a process in which proteins or nucleic acids lose their structure by application of some external stress or compound for example, treatment of proteins with strong acids or bases, high concentrations of inorganic salts, organic compound solvents , or heat....
), exposing the peptide bond

Peptide bond

A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amine group of the other molecule, thereby releasing a molecule of water ....
s that link together amino acids. HCl also activates pepsin

Pepsin

Pepsin is an enzyme that is released by the gastric chief cells in the stomach and which degrades food proteins into peptides. Pepsin was discovered in 1836 by Theodor Schwann who also coined this enzyme's name from the Greek language word pepsis, meaning digestion ....
, an endopeptidase, allowing it to help digestion by breaking specific peptide bonds, a process known as proteolysis

Proteolysis

Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion....
. Furthermore, the sudden increase in gastric acid secretion following a meal can cause a physiological phenomenon called an alkaline tide

Alkaline tide

Alkaline tide refers to a condition, normally encountered after eating a meal, when stomach acid is released into the stomach causing a temporary increase in pH of the blood....
, 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

Secretion

Secretion is the process of, elaborating and releasing Chemical compound from a cell , or a secreted chemical substance or amount of substance. In contrast to excretion, the substance may have a certain function, rather than being a waste product....
acid in response to three types of stimuli

Stimulus (physiology)

In physiology, a stimulus is a detectable change in the internal or external environment. When a stimulus is applied to a sensory receptor, it elicits or influences a Reflex action via Transduction ....
:

H₂ histamine
Histamine

Histamine is a biogenic amine involved in local immune system as well as regulating physiological function in the gut and acting as a neurotransmitter....
receptors (most significant contribution)
parasympathetic activity via the Vagus nerve
Vagus nerve

The vagus nerve is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem and extends, through the jugular foramen, down below the head , to the neck, chest and abdomen, where it contributes to the innervation of the viscera....
and enteric nervous system
gastrin
Gastrin

In humans, gastrin is a hormone that stimulates secretion of gastric acid by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the stomach, duodenum, and the pancreas....
(least significant contribution, but note that histamine secretion by ECL cells is due in part to gastrin)

Upon stimulation, adenylate cyclase

Adenylate cyclase

Adenylate cyclase is a lyase enzyme....
is activated within the parietal cells. This increases intracellular cyclic AMP

Cyclic adenosine monophosphate

Cyclic adenosine monophosphate is a second messenger that is important in many biological processes. cAMP is derived from adenosine triphosphate and used for intracellular signal transduction in many different organisms....
, which leads to activation of protein kinase A. Protein kinase A phosphorylates proteins involved in the transport of H⁺/K⁺ ATPase

Hydrogen potassium ATPase

Gastric hydrogen potassium ATPase is also known as H+/K+ ATPase...
from the cytoplasm to the cell membrane

Cell membrane

The cell membrane is the interface between the cellular machinery inside the cell and the fluid outside.It is a semipermeable lipid bilayer found in all cell ....
. This causes resorption of K⁺ ions and secretion of H⁺ ions. The pH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
of the secreted fluid can fall 'by' 0.8.

Intrinsic factor

Parietal cells also produce intrinsic factor

Intrinsic factor

Intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the terminal ileum....
. Intrinsic factor is required for the absorption of vitamin B

Cyanocobalamin

Cyanocobalamin is an especially common vitamer of the Vitamin B12. It is the most famous vitamer of the family, because it is chemically the most air-stable, and it is the easiest to crystallize and therefore easiest to purify after it is produced by bacterial fermentation....
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

Nucleotide

Nucleotides are molecules that comprise the structural units of RNA and DNA. Additionally, nucleotides play central roles in metabolism. In that capacity, they serve as sources of chemical energy , participate in cell signaling , and are incorporated into important cofactors of enzymatic reactions ....
metabolism in the bone marrow

Bone marrow

Bone marrow is the flexible biological tissue found in the hollow interior of bones. In adults, marrow in large bones produces new blood cells....
.

Diseases of parietal cells

Peptic ulcer
Peptic ulcer

A peptic ulcer, also known as ulcus pepticum, PUD or peptic ulcer disease, is an ulcer of an area of the gastrointestinal tract that is usually acidic and thus extremely painful....
s 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
Pirenzepine

Pirenzepine is used in the treatment of peptic ulcers, as it reduces gastric acid secretion and reduces muscle spasm. It is in a class of drugs known as muscarinic receptor antagonists - acetylcholine being the neurotransmitter of the parasympathetic nervous system which initiates the rest-and-digest state , the result being an increase in g...
or H₂ antihistamine
Antihistamine

An H1 antagonist is a histamine antagonist of the histamine H1 receptor that serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergy....
s can reduce acid secretion. Proton pump inhibitor
Proton pump inhibitor

Proton pump inhibitors are a group of Medications whose main action is a pronounced and long-lasting reduction of gastric acid production. They are the most potent inhibitors of acid secretion available today....
s are more potent at reducing gastric acid production since that is the final common pathway of all stimulation of acid production.

In pernicious anemia
Pernicious anemia

Pernicious anemia is a form of megaloblastic anemia due to vitamin B-12 Avitaminosis, caused by impaired absorption of vitamin B-12 due to the absence of intrinsic factor in the setting of atrophic gastritis, and more specifically of loss of stomach parietal cells....
, autoantibodies
Autoantibody

An autoantibody is an antibody manufactured by the immune system that is directed against one or more of the individual's own proteins.It is derived from the Greek "auto" which means "self", "anti" which means "against" and "body"....
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
Achlorhydria

Achlorhydria and hypochlorhydria refer to states where the production of gastric acid in the stomach is absent or low, respectively. It is associated with various other medical problems....
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
Gastroenteritis

Gastroenteritis is inflammation of the gastrointestinal tract, involving both the stomach and the small intestine and resulting in acute diarrhea....
.

External links

- Digestive System: Alimentary Canal: fundic stomach, gastric glands, lumen"

Parietal cell

Acid production

Intrinsic factor

Diseases of parietal cells

See also

External links