Parietal cells, or
oxyntic cells, are the
stomachThe stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
epitheliumEpithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s that secrete
gastric acidGastric acid is a digestive fluid, formed in the stomach. It has a pH of 1 to 2 and is composed of hydrochloric acid , and large quantities of potassium chloride and sodium chloride...
and
intrinsic factorIntrinsic factor also known as gastric 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 small intestine...
.
AcetylcholineThe chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
(
M3 receptorsThe muscarinic acetylcholine receptor M1, also known as the cholinergic receptor, muscarinic 1, is a muscarinic receptor.This receptor is found mediating slow EPSP at the ganglion in the postganglionic nerve, is common in exocrine glands and in the CNS.It is predominantly found bound to G proteins...
) and
gastrinIn humans, gastrin is a peptide 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 antrum of the stomach, duodenum, and the pancreas...
(
CCK2 receptorsThe cholecystokinin B receptor also known as CCKBR or CCK2 is a protein that in humans is encoded by the CCKBR gene.This gene encodes a G protein-coupled receptor for gastrin and cholecystokinin , regulatory peptides of the brain and gastrointestinal tract...
). The histamine receptors act by increasing intracellular
cAMPCyclic adenosine monophosphate is a second messenger important in many biological processes...
, whereas the muscarinic and gastrin receptors increase intracellular Ca
2+ levels. Both cAMP and Ca
2+ 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 transportActive transport is the movement of a substance against its concentration gradient . In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose, and amino acids. If the process uses chemical energy, such as from adenosine...
into the stomach. The enzyme
hydrogen potassium ATPaseGastric hydrogen potassium ATPase is also known as H+/K+ ATPase- Function and location :The gastric hydrogen potassium ATPase or H+/K+ ATPase is the proton pump of the stomach and, as such, is the enzyme primarily responsible for the acidification of the stomach contents...
(H
+/K
+ ATPase) is unique to the parietal cells and transports the H
+ against a
concentrationIn chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume 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
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
carbonic anhydraseThe carbonic anhydrases form a family of enzymes that catalyze the rapid interconversion of carbon dioxide and water to bicarbonate and protons , a reversible reaction that occurs rather slowly in the absence of a catalyst...
converts one molecule of carbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and one molecule of water indirectly into a bicarbonateIn inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
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
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....
.
- Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
(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
Gastric hydrogen potassium ATPase is also known as H+/K+ ATPase- Function and location :The gastric hydrogen potassium ATPase or H+/K+ ATPase is the proton pump of the stomach and, as such, is the enzyme primarily responsible for the acidification of the stomach contents...
.
The resulting highly-acid environment causes
proteinProteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s from food to unfold (or
denatureDenaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat...
), exposing the
peptide bondThis article is about the peptide link found within biological molecules, such as proteins. A similar article for synthetic molecules is being created...
s 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
proteolysisProteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...
. Furthermore, the sudden increase in gastric acid secretion following a meal can cause a physiological phenomenon called an
alkaline tideAlkaline 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
secreteSecretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...
acid in response to three types of
stimuliIn physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
:
- H2 histamine
Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...
receptors (most significant contribution)
- parasympathetic activity via the Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
and enteric nervous system
- gastrin
In humans, gastrin is a peptide 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 antrum of 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 cyclaseAdenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell ....
is activated within the parietal cells. This increases intracellular
cyclic AMPCyclic adenosine monophosphate is a second messenger important in many biological processes...
, which leads to activation of protein kinase A. Protein kinase A phosphorylates proteins involved in the transport of
H+/K+ ATPaseGastric hydrogen potassium ATPase is also known as H+/K+ ATPase- Function and location :The gastric hydrogen potassium ATPase or H+/K+ ATPase is the proton pump of the stomach and, as such, is the enzyme primarily responsible for the acidification of the stomach contents...
from the cytoplasm to the
cell membraneThe cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
. This causes resorption of K
+ ions and secretion of H
+ ions. The
pHIn chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of the secreted fluid can fall 'by' 0.8.
Intrinsic factor
Parietal cells also produce
intrinsic factorIntrinsic factor also known as gastric 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 small intestine...
. Intrinsic factor is required for the absorption of
Vitamin B
Parietal cells, or oxyntic cells, are the stomachThe stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
epitheliumEpithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s that secrete
gastric acidGastric acid is a digestive fluid, formed in the stomach. It has a pH of 1 to 2 and is composed of hydrochloric acid , and large quantities of potassium chloride and sodium chloride...
and
intrinsic factorIntrinsic factor also known as gastric 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 small intestine...
.
AcetylcholineThe chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
(
M3 receptorsThe muscarinic acetylcholine receptor M1, also known as the cholinergic receptor, muscarinic 1, is a muscarinic receptor.This receptor is found mediating slow EPSP at the ganglion in the postganglionic nerve, is common in exocrine glands and in the CNS.It is predominantly found bound to G proteins...
) and
gastrinIn humans, gastrin is a peptide 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 antrum of the stomach, duodenum, and the pancreas...
(
CCK2 receptorsThe cholecystokinin B receptor also known as CCKBR or CCK2 is a protein that in humans is encoded by the CCKBR gene.This gene encodes a G protein-coupled receptor for gastrin and cholecystokinin , regulatory peptides of the brain and gastrointestinal tract...
). The histamine receptors act by increasing intracellular
cAMPCyclic adenosine monophosphate is a second messenger important in many biological processes...
, whereas the muscarinic and gastrin receptors increase intracellular Ca
2+ levels. Both cAMP and Ca
2+ 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 transportActive transport is the movement of a substance against its concentration gradient . In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose, and amino acids. If the process uses chemical energy, such as from adenosine...
into the stomach. The enzyme
hydrogen potassium ATPaseGastric hydrogen potassium ATPase is also known as H+/K+ ATPase- Function and location :The gastric hydrogen potassium ATPase or H+/K+ ATPase is the proton pump of the stomach and, as such, is the enzyme primarily responsible for the acidification of the stomach contents...
(H
+/K
+ ATPase) is unique to the parietal cells and transports the H
+ against a
concentrationIn chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume 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
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
carbonic anhydraseThe carbonic anhydrases form a family of enzymes that catalyze the rapid interconversion of carbon dioxide and water to bicarbonate and protons , a reversible reaction that occurs rather slowly in the absence of a catalyst...
converts one molecule of carbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and one molecule of water indirectly into a bicarbonateIn inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
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
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....
.
- Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
(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
Gastric hydrogen potassium ATPase is also known as H+/K+ ATPase- Function and location :The gastric hydrogen potassium ATPase or H+/K+ ATPase is the proton pump of the stomach and, as such, is the enzyme primarily responsible for the acidification of the stomach contents...
.
The resulting highly-acid environment causes
proteinProteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s from food to unfold (or
denatureDenaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat...
), exposing the
peptide bondThis article is about the peptide link found within biological molecules, such as proteins. A similar article for synthetic molecules is being created...
s 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
proteolysisProteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...
. Furthermore, the sudden increase in gastric acid secretion following a meal can cause a physiological phenomenon called an
alkaline tideAlkaline 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
secreteSecretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...
acid in response to three types of
stimuliIn physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
:
- H2 histamine
Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...
receptors (most significant contribution)
- parasympathetic activity via the Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
and enteric nervous system
- gastrin
In humans, gastrin is a peptide 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 antrum of 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 cyclaseAdenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell ....
is activated within the parietal cells. This increases intracellular
cyclic AMPCyclic adenosine monophosphate is a second messenger important in many biological processes...
, which leads to activation of protein kinase A. Protein kinase A phosphorylates proteins involved in the transport of
H+/K+ ATPaseGastric hydrogen potassium ATPase is also known as H+/K+ ATPase- Function and location :The gastric hydrogen potassium ATPase or H+/K+ ATPase is the proton pump of the stomach and, as such, is the enzyme primarily responsible for the acidification of the stomach contents...
from the cytoplasm to the
cell membraneThe cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
. This causes resorption of K
+ ions and secretion of H
+ ions. The
pHIn chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of the secreted fluid can fall 'by' 0.8.
Intrinsic factor
Parietal cells also produce
intrinsic factorIntrinsic factor also known as gastric 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 small intestine...
. Intrinsic factor is required for the absorption of
Vitamin B
Parietal cells, or oxyntic cells, are the stomachThe stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
epitheliumEpithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s that secrete
gastric acidGastric acid is a digestive fluid, formed in the stomach. It has a pH of 1 to 2 and is composed of hydrochloric acid , and large quantities of potassium chloride and sodium chloride...
and
intrinsic factorIntrinsic factor also known as gastric 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 small intestine...
.
AcetylcholineThe chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
(
M3 receptorsThe muscarinic acetylcholine receptor M1, also known as the cholinergic receptor, muscarinic 1, is a muscarinic receptor.This receptor is found mediating slow EPSP at the ganglion in the postganglionic nerve, is common in exocrine glands and in the CNS.It is predominantly found bound to G proteins...
) and
gastrinIn humans, gastrin is a peptide 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 antrum of the stomach, duodenum, and the pancreas...
(
CCK2 receptorsThe cholecystokinin B receptor also known as CCKBR or CCK2 is a protein that in humans is encoded by the CCKBR gene.This gene encodes a G protein-coupled receptor for gastrin and cholecystokinin , regulatory peptides of the brain and gastrointestinal tract...
). The histamine receptors act by increasing intracellular
cAMPCyclic adenosine monophosphate is a second messenger important in many biological processes...
, whereas the muscarinic and gastrin receptors increase intracellular Ca
2+ levels. Both cAMP and Ca
2+ 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 transportActive transport is the movement of a substance against its concentration gradient . In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose, and amino acids. If the process uses chemical energy, such as from adenosine...
into the stomach. The enzyme
hydrogen potassium ATPaseGastric hydrogen potassium ATPase is also known as H+/K+ ATPase- Function and location :The gastric hydrogen potassium ATPase or H+/K+ ATPase is the proton pump of the stomach and, as such, is the enzyme primarily responsible for the acidification of the stomach contents...
(H
+/K
+ ATPase) is unique to the parietal cells and transports the H
+ against a
concentrationIn chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume 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
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
carbonic anhydraseThe carbonic anhydrases form a family of enzymes that catalyze the rapid interconversion of carbon dioxide and water to bicarbonate and protons , a reversible reaction that occurs rather slowly in the absence of a catalyst...
converts one molecule of carbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and one molecule of water indirectly into a bicarbonateIn inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
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
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....
.
- Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
(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
Gastric hydrogen potassium ATPase is also known as H+/K+ ATPase- Function and location :The gastric hydrogen potassium ATPase or H+/K+ ATPase is the proton pump of the stomach and, as such, is the enzyme primarily responsible for the acidification of the stomach contents...
.
The resulting highly-acid environment causes
proteinProteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s from food to unfold (or
denatureDenaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat...
), exposing the
peptide bondThis article is about the peptide link found within biological molecules, such as proteins. A similar article for synthetic molecules is being created...
s 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
proteolysisProteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.-Purposes:Proteolysis is used by the cell for several purposes...
. Furthermore, the sudden increase in gastric acid secretion following a meal can cause a physiological phenomenon called an
alkaline tideAlkaline 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
secreteSecretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...
acid in response to three types of
stimuliIn physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
:
- H2 histamine
Histamine is an organic nitrogen compound involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter. Histamine triggers the inflammatory response. As part of an immune response to foreign pathogens, histamine is produced by...
receptors (most significant contribution)
- parasympathetic activity via the Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
and enteric nervous system
- gastrin
In humans, gastrin is a peptide 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 antrum of 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 cyclaseAdenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell ....
is activated within the parietal cells. This increases intracellular
cyclic AMPCyclic adenosine monophosphate is a second messenger important in many biological processes...
, which leads to activation of protein kinase A. Protein kinase A phosphorylates proteins involved in the transport of
H+/K+ ATPaseGastric hydrogen potassium ATPase is also known as H+/K+ ATPase- Function and location :The gastric hydrogen potassium ATPase or H+/K+ ATPase is the proton pump of the stomach and, as such, is the enzyme primarily responsible for the acidification of the stomach contents...
from the cytoplasm to the
cell membraneThe cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
. This causes resorption of K
+ ions and secretion of H
+ ions. The
pHIn chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of the secreted fluid can fall 'by' 0.8.
Intrinsic factor
Parietal cells also produce
intrinsic factorIntrinsic factor also known as gastric 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 small intestine...
. Intrinsic factor is required for the absorption of
Vitamin B{{ssubVitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins...
in the diet. A long-term deficiency in vitamin B
12 can lead to
megaloblastic anemiaMegaloblastic anemia is an anemia that results from inhibition of DNA synthesis in red blood cell production. When DNA synthesis is impaired, the cell cycle cannot progress from the G2 growth stage to the mitosis stage...
, characterized by large fragile
erythrocyteRed blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...
s. Pernicious Anemia is a condition where intrinsic factor is not produced and leads to the same type of anemia.
Atrophic gastritisAtrophic gastritis is a process of chronic inflammation of the stomach mucosa, leading to loss of gastric glandular cells and their eventual replacement by intestinal and fibrous tissues...
, particularly in the elderly, will cause an inability to absorb B
12 and can lead to deficiencies such as decreased DNA synthesis and
nucleotideNucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
metabolism in the bone marrow.
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 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.
Diseases of parietal cells
- Peptic ulcer
A peptic ulcer, also known as PUD or peptic ulcer disease, is the most common ulcer of an area of the gastrointestinal tract that is usually acidic and thus extremely painful. It is defined as mucosal erosions equal to or greater than 0.5 cm...
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 pirenzepinePirenzepine 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...
or H2 antihistamineAn H1 antagonist is a histamine antagonist of the H1 receptor that serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergic reactions...
s can reduce acid secretion. Proton pump inhibitorProton-pump inhibitors are a group of drugs 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. The group followed and has largely superseded another group of pharmaceuticals with similar...
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 one of many types of the larger family of megaloblastic anemias...
, autoantibodiesAn 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 or hypochlorhydria refers to states where the production of gastric acid in the stomach is absent or low, respectively. It is associated with various other medical problems.-Signs and symptoms:...
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 gastroenteritisGastroenteritis is marked by severe inflammation of the gastrointestinal tract involving both the stomach and small intestine resulting in acute diarrhea and vomiting. It can be transferred by contact with contaminated food and water...
.
See also
- Chief cell
In general, a chief cell is a cell which releases a precursor enzyme. There are two types of chief cells which are most commonly referenced:...
- Fundic glands
The fundus glands are found in the body and fundus of the stomach.They are simple tubes, two or more of which open into a single duct.-Pathology:...
- Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
- Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
- Gastroesophageal reflux disease
Gastroesophageal reflux disease , gastro-oesophageal reflux disease , gastric reflux disease, or acid reflux disease is chronic symptoms or mucosal damage caused by stomach acid coming up from the stomach into the esophagus...
- Discovery and Development of Proton Pump Inhibitors
Proton pump inhibitors block the gastric Hydrogen potassium ATPase and inhibit gastric acid secretion. These drugs have emerged as the treatment of choice for acid-related diseases, including gastroesophageal reflux disease and peptic ulcer disease.-History:Evidence emerged by the end of the...
External links
{{Gastrointestinal physiology}}
{{Human cell types derived primarily from endoderm}}
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