Parietal cells (also known as oxyntic cells) are
epithelial cells
Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercell ...
in the
stomach
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
that secrete
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
(HCl) and
intrinsic factor
Intrinsic factor (IF), cobalamin binding intrinsic factor, also known as gastric intrinsic factor (GIF), is a glycoprotein produced by the parietal cells (in humans) or chief cells (in rodents) of the stomach. It is necessary for the absorption ...
. These
cells are located in the
gastric glands
The gastric glands are glands in the lining of the stomach that play an essential role in the process of digestion. All of the glands have mucus-secreting foveolar cells. Mucus lines the entire stomach, and protects the stomach lining from the ...
found in the
lining
Lining may refer to:
* Lining (sewing), the process of inserting an inner layer of fabric, fur, or other material
* Lining of paintings, the process of restoration paintings by attaching a new canvas to the back of the existing one
* Brake linin ...
of the
fundus and
body
Body may refer to:
In science
* Physical body, an object in physics that represents a large amount, has mass or takes up space
* Body (biology), the physical material of an organism
* Body plan, the physical features shared by a group of anima ...
regions of the stomach.
They contain an extensive secretory network of
canaliculi from which the HCl is secreted by
active transport
In cellular biology, ''active transport'' is the movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. Active transport requires cellul ...
into the stomach. The enzyme
hydrogen potassium ATPase
Gastric hydrogen potassium ATPase, also known as H+/K+ ATPase, is an enzyme which functions to acidify the stomach. It is a member of the P-type ATPases, also known as E1-E2 ATPases due to its two states.
Biological function and location
The ...
(H
+/K
+ ATPase) is unique to the parietal cells and transports the H
+ against a
concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', '' number concentration'', ...
gradient of about 3 million to 1, which is the steepest ion gradient formed in the human body. Parietal cells are primarily
regulated
Regulation is the management of complex systems according to a set of rules and trends. In systems theory, these types of rules exist in various fields of biology and society, but the term has slightly different meanings according to context. Fo ...
via
histamine
Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered ...
,
acetylcholine and
gastrin signalling from both central and local modulators.
Structure
Canaliculus
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 parietal cell membrane 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.
Function
Hydrochloric acid secretion
Hydrochloric acid is formed in the following manner:
* Hydrogen ions are formed from the dissociation of carbonic acid. Water is a very minor source of hydrogen ions in comparison to carbonic acid. Carbonic acid is formed from
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
and water by
carbonic anhydrase.
* The bicarbonate ion (HCO
3−) 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 Alkaline tide refers to a condition, normally encountered after eating a meal, where during the production of hydrochloric acid by the parietal cells in the stomach, the parietal cells secrete bicarbonate ions across their basolateral membranes and ...
phenomenon.
*
Potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosph ...
(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. These pumps are increased in number on luminal side by fusion of tubulovesicles during activation of parietal cells and removed during deactivation. This pump maintains a million-fold difference in proton concentration. ATP is provided by the numerous mitochondria.
![Parietal cells](https://upload.wikimedia.org/wikipedia/commons/5/5a/Parietal_cells.jpg)
As a result of the cellular export of hydrogen ions, the gastric lumen is maintained as a highly acidic environment. The acidity aids in digestion of food by promoting the unfolding (or
denaturing) of ingested
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s. As proteins unfold, the
peptide bonds
In organic chemistry, a peptide bond is an amide type of covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another, along a peptide or protein cha ...
linking component
amino acids are exposed. Gastric HCl simultaneously cleaves
pepsinogen, a
zymogen
In biochemistry, a zymogen (), also called a proenzyme (), is an inactive precursor of an enzyme. A zymogen requires a biochemical change (such as a hydrolysis reaction revealing the active site, or changing the configuration to reveal the activ ...
, into active
pepsin
Pepsin is an endopeptidase that breaks down proteins into smaller peptides. It is produced in the gastric chief cells of the stomach lining and is one of the main digestive enzymes in the digestive systems of humans and many other animals, w ...
, an endopeptidase that advances the digestive process by breaking the now-exposed peptide bonds, a process known as
proteolysis.
Regulation
Parietal cells
secrete 440px
Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical ...
acid in response to three types of
stimuli
A stimulus is something that causes a physiological response. It may refer to:
* Stimulation
** Stimulus (physiology), something external that influences an activity
** Stimulus (psychology), a concept in behaviorism and perception
* Stimulus (eco ...
:
*
Histamine
Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered ...
, stimulates
H2 histamine receptors (most significant contribution).
*
Acetylcholine(ACh), from
parasympathetic activity via the
vagus nerve
The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and righ ...
and enteric nervous system, stimulating
M3 receptors.
*
Gastrin, stimulating
CCK2 receptors (least significant contribution, but also causes histamine secretion by local
ECL cells
Enterochromaffin-like cells or ECL cells are a type of neuroendocrine cell found in the gastric glands of the gastric mucosa beneath the epithelium, in particular in the vicinity of parietal cells, that aid in the production of gastric acid via th ...
)
Activation of histamine through H
2 receptor causes increases in the intracellular
cAMP
Camp may refer to:
Outdoor accommodation and recreation
* Campsite or campground, a recreational outdoor sleeping and eating site
* a temporary settlement for nomads
* Camp, a term used in New England, Northern Ontario and New Brunswick to descri ...
level while ACh through M
3 receptor and gastrin through CCK2 receptor increases intracellular calcium level. These receptors are present on basolateral side of membrane.
Increased cAMP level results in increased protein kinase A. Protein kinase A phosphorylates proteins involved in the transport of
H+/K+-ATPase from the cytoplasm to the
cell membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...
. This causes resorption of K
+ ions and secretion of H
+ ions. The
pH of the secreted fluid can fall by 0.8.
Gastrin primarily induces acid-secretion indirectly, increasing histamine synthesis in
ECL cells
Enterochromaffin-like cells or ECL cells are a type of neuroendocrine cell found in the gastric glands of the gastric mucosa beneath the epithelium, in particular in the vicinity of parietal cells, that aid in the production of gastric acid via th ...
, which in turn signal parietal cells via histamine release and H
2 stimulation. Gastrin itself has no effect on the maximum histamine-stimulated gastric acid secretion.
The effect of histamine, acetylcholine and gastrin is synergistic, that is, effect of two simultaneously is more than additive of effect of the two individually. It helps in non-linear increase of secretion with stimuli physiologically.
Intrinsic factor secretion
Parietal cells also produce a
glycoprotein known as
intrinsic factor
Intrinsic factor (IF), cobalamin binding intrinsic factor, also known as gastric intrinsic factor (GIF), is a glycoprotein produced by the parietal cells (in humans) or chief cells (in rodents) of the stomach. It is necessary for the absorption ...
. Intrinsic factor is required for the absorption of
vitamin B
B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism and synthesis of red blood cells. Though these vitamins share similar names (B1, B2, B3, etc.), they are chemically distinct compounds that often coex ...
in the diet. A long-term
deficiency in vitamin B12 can lead to
megaloblastic anemia
Megaloblastic anemia is a type of macrocytic anemia. An anemia is a red blood cell defect that can lead to an undersupply of oxygen. Megaloblastic anemia results from inhibition of DNA synthesis during red blood cell production. When DNA synth ...
, characterized by large fragile
red blood cells.
Pernicious anaemia
Pernicious anemia is a type of vitamin B12 deficiency anemia, a disease in which not enough red blood cells are produced due to the malabsorption of vitamin B12. Malabsorption in pernicious anemia results from the lack or loss of intrinsic ...
results from autoimmune destruction of gastric parietal cells, precluding the synthesis of intrinsic factor and, by extension, absorption of vitamin B
12. Pernicious anemia also leads to megaloblastic anemia.
Atrophic gastritis
Atrophic gastritis is a process of chronic inflammation of the gastric mucosa of the stomach, leading to a loss of gastric glandular cells and their eventual replacement by intestinal and fibrous tissues. As a result, the stomach's secretion o ...
, particularly in the elderly, will cause an inability to absorb B
12 and can lead to deficiencies such as decreased DNA synthesis and
nucleotide
Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecule ...
metabolism in the bone marrow.
Clinical significance
![GASTRIC PARIETAL CELL ANTIBODIES](https://upload.wikimedia.org/wikipedia/commons/f/f0/GASTRIC_PARIETAL_CELL_ANTIBODIES.jpg)
* ''
Peptic ulcer
Peptic ulcer disease (PUD) is a break in the inner lining of the stomach, the first part of the small intestine, or sometimes the lower esophagus. An ulcer in the stomach is called a gastric ulcer, while one in the first part of the intestines ...
s'' can result from over-acidity in the stomach. Antacids can be used to enhance the natural tolerance of the gastric lining.
Antimuscarinic
A muscarinic receptor antagonist (MRA) is a type of anticholinergic agent that blocks the activity of the muscarinic acetylcholine receptor. The muscarinic receptor is a protein involved in the transmission of signals through certain parts of th ...
drugs such as
pirenzepine
Pirenzepine (Gastrozepin), an M1 selective antagonist, 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 - acetylchol ...
or H
2 antihistamine
Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic (not patented) drug that can be bought without a prescription and provid ...
s can reduce acid secretion.
Proton pump inhibitor
Proton-pump inhibitors (PPIs) are a class of medications that cause a profound and prolonged reduction of stomach acid production. They do so by irreversibly inhibiting the stomach's H+/K+ ATPase proton pump.
They are the most potent inhibitor ...
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 is a type of vitamin B12 deficiency anemia, a disease in which not enough red blood cells are produced due to the malabsorption of vitamin B12. Malabsorption in pernicious anemia results from the lack or loss of intrinsic fa ...
'',
autoantibodies directed against parietal cells or intrinsic factor cause a reduction in vitamin B
12 absorption. It can be treated with injections of replacement vitamin B
12 (
methylcobalamin
Methylcobalamin (mecobalamin, MeCbl, or MeB) is a cobalamin, a form of vitamin B. It differs from cyanocobalamin in that the cyano group at the cobalt is replaced with a methyl group. Methylcobalamin features an octahedral cobalt(III) centre and ...
,
hydroxocobalamin
Hydroxocobalamin, also known as vitamin B12a and hydroxycobalamin, is a vitamin found in food and used as a dietary supplement. As a supplement it is used to treat vitamin B12 deficiency including pernicious anemia. Other uses include treatment ...
or
cyanocobalamin
Cyanocobalamin is a form of vitamin used to treat vitamin deficiency except in the presence of cyanide toxicity. The deficiency may occur in pernicious anemia, following surgical removal of the stomach, with fish tapeworm, or due to bowel ...
).
* ''
Achlorhydria
Achlorhydria and hypochlorhydria refer to states where the production of hydrochloric acid in gastric secretions of the stomach and other digestive organs is absent or low, respectively. It is associated with various other medical problems.
Sig ...
'' is another
autoimmune
In immunology, autoimmunity is the system of immune responses of an organism against its own healthy cells, tissues and other normal body constituents. Any disease resulting from this type of immune response is termed an "autoimmune disease". ...
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.
See also
*
Gastric chief cell
A gastric chief cell (or peptic cell, or gastric zymogenic cell) is a type of gastric gland cell that releases pepsinogen and gastric lipase. It is the cell responsible for secretion of chymosin in ruminant animals. The cell stains basophilic upo ...
*
Digestion
Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...
*
Gastroesophageal reflux disease
Gastroesophageal reflux disease (GERD) or gastro-oesophageal reflux disease (GORD) is one of the upper gastrointestinal chronic diseases where stomach content persistently and regularly flows up into the esophagus, resulting in symptoms and/ ...
*
Discovery and Development of Proton Pump Inhibitors
*
List of human cell types derived from the germ layers
References
External links
Illustration of Chief cells and Parietal cells at anatomyatlases.org* - Digestive System: Alimentary Canal: fundic stomach, gastric glands, lumen"
*
*
Parietal cell antibody
{{Authority control
Epithelial cells
Animal cells
Human cells
Acid secreting cells
Stomach