Information about 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 consisting mainly of hydrochloric acid (HCl), and small quantities of potassium chloride (KCl) and sodium chloride (NaCl).
Gastric acid is produced by parietal cells (also called oxyntic cells) in the stomach. Its secretion is a complex and relatively energetically expensive process. Parietal cells contain an extensive secretory network (called canaliculi) from which the gastric acid is secreted into the lumen of the stomach. These cells are part of epithelial fundic glands in the gastric mucosa. The pH of gastric acid is 2 to 3 in the human stomach lumen, the acidity being maintained by the proton pump H+/K+ ATPase. The parietal cell releases bicarbonate into the blood stream in the process, which causes the temporary rise of pH in the blood, known as alkaline tide.
The resulting highly acidic environment in the stomach lumen causes proteins from food to lose their characteristic folded structure (or denature). This exposes the protein's peptide bonds.The chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen and renin). The gastric acid activates pepsinogen into pepsin - this enzyme then helps digestion by breaking the bonds linking amino acids, a process known as proteolysis. In addition, many microorganisms have their growth inhibited by such an acidic environment which is helpful to prevent infection.
The highest concentration that it reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is about 0.8, but the acid gets diluted in the stomach lumen to the pH between 2 and 3.
At first, negative chloride ions and sodium ions get secreted actively from the cytoplasm of the parietal cell into the lumen of the canaliculus. This creates a negative potential of -40 mV (millivolts)to -70 mV across the membrane that enables the diffusion of potassium ions and a small number of sodium ions from the cytoplasm into the canaliculus.
Another step is the production of hydrogen ions in the cytoplasm of parietal cells. The enzyme carbonic anhydrase catalyses the reaction between carbon dioxide and water, in which carbonic acid is produced. This acid immediately dissociates into hydrogen ions and hydrogen carbonate ions. The hydrogen ions leave the cell by the aid of H+/K+ ATPase antiporter.
At the same time sodium ions are actively reabsorbed. This means the largest amount of secreted K+ and Na+ ions return into the cytoplasm. In the canaliculus, secreted hydrogen and chloride ions combine into HCl and are then secreted into the lumen of the oxyntic gland.
There are three phases in the secretion of gastric acid: 1. The cephalic phase: 30% of the total gastric acid to be produced is stimulated by anticipation of eating and the smell or taste of food 2. The gastric phase: 60% of the acid secreted is stimulated by the distention of the stomach with food. Plus, digestion produces proteins, which causes even more gastrin production 3. The intestinal phase: the remaining 10% of acid is secreted when chyme enters the small intestine, and is stimulated by small intestine distention.
The production of gastric acid in the stomach is tightly regulated by positive regulators and negative feedback mechanisms. Four types of cells are involved in this process: parietal cells, G cells, D cells and enterochromaffine-like cells. Besides this, the endings of the vagus nerve (X) and the intramural nervous plecus in the digestive tract influence the secretion significantly.
Nerve endings in the stomach secrete two stimulatory neurotransmitters: acetylcholine and gastrin-releasing peptide. Their action is both direct on parietal cells and mediated through the secretion of gastrin from G cells and histamine from enterochromaffine-like cells. Gastrin acts on parietal cells directly and indirectly too, by stimulating the release of histamine.
The release of histamine is the most important positive regulation mechanism of the secretion of gastric acid in the stomach. Its release is stimulated by gastrin and acetylcholine and inhibited by somatostatin.
The carbonic acid instantly dissociates into carbon dioxide and water, then gets eliminated through urine.
In Zollinger-Ellison syndrome and hypercalcemia, there are increased gastrin levels, leading to excess gastric acid production, which can cause gastric ulcers.
In diseases featuring excess vomiting, patients develop hypochloremic metabolic alkalosis (decreased blood acidity by H+ and chlorine depletion).
..... Click the link for more information.
Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the formula NaCl.
..... Click the link for more information.
..... Click the link for more information.
Physiology
)
Diagram summarising control of stomach acid secretion, emphasising interaction between the body and antrum.
The resulting highly acidic environment in the stomach lumen causes proteins from food to lose their characteristic folded structure (or denature). This exposes the protein's peptide bonds.The chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen and renin). The gastric acid activates pepsinogen into pepsin - this enzyme then helps digestion by breaking the bonds linking amino acids, a process known as proteolysis. In addition, many microorganisms have their growth inhibited by such an acidic environment which is helpful to prevent infection.
Secretion
The gastric acid secretion happens in several steps. Chloride and hydrogen ions are secreted separately from the cytoplasm of parietal cells and get combined into HCl only in their canaliculi. Gastric acid is then secreted into the lumen of the oxyntic gland and gradually reaches the main stomach lumen.The highest concentration that it reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial blood, but almost exactly isotonic with other bodily fluids. The lowest pH of the secreted acid is about 0.8, but the acid gets diluted in the stomach lumen to the pH between 2 and 3.
At first, negative chloride ions and sodium ions get secreted actively from the cytoplasm of the parietal cell into the lumen of the canaliculus. This creates a negative potential of -40 mV (millivolts)to -70 mV across the membrane that enables the diffusion of potassium ions and a small number of sodium ions from the cytoplasm into the canaliculus.
Another step is the production of hydrogen ions in the cytoplasm of parietal cells. The enzyme carbonic anhydrase catalyses the reaction between carbon dioxide and water, in which carbonic acid is produced. This acid immediately dissociates into hydrogen ions and hydrogen carbonate ions. The hydrogen ions leave the cell by the aid of H+/K+ ATPase antiporter.
At the same time sodium ions are actively reabsorbed. This means the largest amount of secreted K+ and Na+ ions return into the cytoplasm. In the canaliculus, secreted hydrogen and chloride ions combine into HCl and are then secreted into the lumen of the oxyntic gland.
There are three phases in the secretion of gastric acid: 1. The cephalic phase: 30% of the total gastric acid to be produced is stimulated by anticipation of eating and the smell or taste of food 2. The gastric phase: 60% of the acid secreted is stimulated by the distention of the stomach with food. Plus, digestion produces proteins, which causes even more gastrin production 3. The intestinal phase: the remaining 10% of acid is secreted when chyme enters the small intestine, and is stimulated by small intestine distention.
Regulation of secretion
Gastric acid production is regulated by both the autonomic nervous system and several hormones. The parasympathetic nervous system, via the vagus nerve, and the hormone gastrin stimulate the parietal cell to produce gastric acid, both directly acting on parietal cells and indirectly, through the stimulation of the secretion of the hormone histamine from enterochromaffine-like cells (ELC). Vasoactive intestinal peptide, cholecystokinin, and secretin all inhibit production.The production of gastric acid in the stomach is tightly regulated by positive regulators and negative feedback mechanisms. Four types of cells are involved in this process: parietal cells, G cells, D cells and enterochromaffine-like cells. Besides this, the endings of the vagus nerve (X) and the intramural nervous plecus in the digestive tract influence the secretion significantly.
Nerve endings in the stomach secrete two stimulatory neurotransmitters: acetylcholine and gastrin-releasing peptide. Their action is both direct on parietal cells and mediated through the secretion of gastrin from G cells and histamine from enterochromaffine-like cells. Gastrin acts on parietal cells directly and indirectly too, by stimulating the release of histamine.
The release of histamine is the most important positive regulation mechanism of the secretion of gastric acid in the stomach. Its release is stimulated by gastrin and acetylcholine and inhibited by somatostatin.
Neutralization
In the duodenum, gastric acid is neutralized by sodium bicarbonate. This also blocks gastric enzymes that have their optima in the acid range of pH. The secretion of sodium bicarbonate from the pancreas is stimulated by secretin. This polypeptide hormone gets activated and secreted from so-called S cells in the mucosa of the duodenum and jejunum when the pH in duodenum falls below 4.5 to 5.0. The neutralization is described by the equation:- : HCl + NaHCO3 → NaCl + H2CO3
The carbonic acid instantly dissociates into carbon dioxide and water, then gets eliminated through urine.
Safety mechanisms
There are several safety mechanisms that prevent the damage of gastric epithelium. Nonetheless, when due to different reasons these fail (e.g. because of excess acid production), this can lead to heartburn or peptic ulcers.Role in disease
In hypochlorhydria and achlorhydria, there is low or no gastric acid in the stomach, potentially leading to problems as the disinfectant properties of the gastric lumen are decreased. In such conditions, there is greater risk of infections of the digestive tract (such as infection with Vibrio or Helicobacter bacteria).In Zollinger-Ellison syndrome and hypercalcemia, there are increased gastrin levels, leading to excess gastric acid production, which can cause gastric ulcers.
In diseases featuring excess vomiting, patients develop hypochloremic metabolic alkalosis (decreased blood acidity by H+ and chlorine depletion).
Pharmacology
The proton pump enzyme is the target of proton pump inhibitors, used to increase gastric pH in diseases which feature excess acid. H2 antagonists indirectly decrease gastric acid production. Antacids neutralize existing acid.External links
See also
Digestive system, physiology: gastrointestinal physiology | |
|---|---|
| Enteric nervous system | Meissner's plexus - Auerbach's plexus |
| Exocrine | Chief cells (Pepsinogen) - Parietal cells (Gastric acid, Intrinsic factor) - Goblet cells (Mucus) |
| Endocrine/paracrine | G cells (gastrin), D cells (somatostatin) - ECL cells (Histamine) - enterogastrone: I cells (CCK), K cells (GIP), S cells (secretin) |
| Border | Brunner's glands - Paneth cells - Enterocytes |
| Fluids | Saliva - Bile - Intestinal juice - Gastric juice - Pancreatic juice |
| Processes | Swallowing - Vomiting - Peristalsis (Interstitial cell of Cajal) - Migrating motor complex - Borborygmus - Gastrocolic reflex - Segmentation contractions - Defecation |
Secretion is the process of segregating, elaborating, and releasing chemicals from a cell, or a secreted chemical substance or amount of substance.
Eukaryotic cells have a highly evolved process of secretion.
..... Click the link for more information.
Eukaryotic cells have a highly evolved process of secretion.
..... Click the link for more information.
In anatomy, the stomach is a bean-shaped hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. The word stomach is derived from the Latin stomachus, which derives from the Greek word
..... Click the link for more information.
..... Click the link for more information.
Enzymes are proteins that catalyze (i.e. accelerate) chemical reactions.[1] In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products.
..... Click the link for more information.
..... Click the link for more information.
Intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B 12 later on in the terminal ileum.
..... Click the link for more information.
..... Click the link for more information.
ACID (Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably. In the context of databases, a single logical operation on the data is called a transaction.
..... Click the link for more information.
..... Click the link for more information.
This article is about chemical solutions. For other uses, see Solution (disambiguation).
In chemistry, a solution is a homogeneous mixture composed of two or more substances...... Click the link for more information.
hydrochloric acid is the aqueous (water-based) solution of hydrogen chloride gas (HCl). It is a strong acid, the major component of gastric acid and of wide industrial use. Hydrochloric acid must be handled with appropriate safety precautions because it is a highly corrosive liquid.
..... Click the link for more information.
..... Click the link for more information.
The chemical compound potassium chloride (KCl) is a metal halide composed of potassium and chlorine. In its pure state it is odorless. It has a white or colorless vitreous crystal, with a crystal structure that cleaves easily in three directions.
..... Click the link for more information.
..... Click the link for more information.
- For sodium in the diet, see salt.
Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the formula NaCl.
..... Click the link for more information.
Parietal cells (also called oxyntic cells) are the stomach epithelium cells which secrete gastric acid and intrinsic factor.
..... Click the link for more information.
Acid production
Parietal cells produce gastric acid (hydrochloric acid) in response to histamine (via H2..... Click the link for more information.
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, eg for secretion. The membrane of parietal cells is dynamic; the numbers of canaliculi rise and fall according to secretory need.
..... Click the link for more information.
..... Click the link for more information.
epithelium is a tissue composed of a layer of cells. Epithelium lines both the outside (skin) and the inside cavities and lumen of bodies. The outermost layer of our skin is composed of dead stratified squamous, keratinized epithelial cells.
..... Click the link for more information.
..... Click the link for more information.
The fundus glands (or fundic glands, or gastric 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.
..... Click the link for more information.
They are simple tubes, two or more of which open into a single duct.
..... Click the link for more information.
The gastric mucosa is the mucous membrane layer of the stomach which contains the glands and the gastric pits. It is thick and its surface is smooth, soft, and velvety.
..... Click the link for more information.
..... Click the link for more information.
..... Click the link for more information.
A lumen (pl. lumina) is an inner space, lining or cavity.
..... Click the link for more information.
- The interior of a vessel within the body, such as the small central space in an artery or vein, or any of their relating vessels through which blood flows.
..... Click the link for more information.
proton pump is an integral membrane protein that is capable of moving protons across the membrane of a cell, mitochondrion, or other subcellular compartment.
..... Click the link for more information.
Function
..... Click the link for more information.
Identifiers
Symbol ATP4B
Entrez 496
HUGO 820
OMIM 137217
RefSeq NM_000705
UniProt P51164
Other data
EC number 3.6.3.10
Locus Chr. 13 q34 Gastric hydrogen potassium ATPase is also known as H+/K+
..... Click the link for more information.
Symbol ATP4B
Entrez 496
HUGO 820
OMIM 137217
RefSeq NM_000705
UniProt P51164
Other data
EC number 3.6.3.10
Locus Chr. 13 q34 Gastric hydrogen potassium ATPase is also known as H+/K+
..... Click the link for more information.
bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid.
The bicarbonate ion (hydrogen carbonate) is an anion with the empirical formula HCO3
..... Click the link for more information.
Chemical properties
The bicarbonate ion (hydrogen carbonate) is an anion with the empirical formula HCO3
..... Click the link for more information.
Alkaline Tide refers to a condition, normally encountered after eating a meal, when stomach acid is released into the stomach that causes a temporary increase in pH of the blood. This is a natural bodily function.
..... Click the link for more information.
..... Click the link for more information.
Proteins are large 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 residues.
..... Click the link for more information.
..... Click the link for more information.
Denaturation is the alteration of a protein or nucleic acid's shape through some form of external stress (for example, by applying heat, acid or alkali), in such a way that it will no longer be able to carry out its cellular function.
..... Click the link for more information.
..... Click the link for more information.
A peptide bond is a chemical bond that is formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O).
..... Click the link for more information.
..... Click the link for more information.
Pepsin is a digestive protease (EC 3.4.23.1 ) released by the chief cells in the stomach that functions to degrade food proteins into peptides.
According to American Heritage Dictionary, pepsin derives from the Greek word pepsis, meaning digestion (
..... Click the link for more information.
According to American Heritage Dictionary, pepsin derives from the Greek word pepsis, meaning digestion (
..... Click the link for more information.
Enzymes are proteins that catalyze (i.e. accelerate) chemical reactions.[1] In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products.
..... Click the link for more information.
..... Click the link for more information.
amino acid is a molecule that contains both amine and carboxyl functional groups. In biochemistry, this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent.
..... Click the link for more information.
..... Click the link for more information.
Proteolysis is the directed degradation (digestion) of proteins by cellular enzymes called proteases or by intramolecular digestion.
..... Click the link for more information.
Purposes
Proteolysis is used by the cell for several purposes...... Click the link for more information.
microorganism (also spelled as microrganism) or microbe is an organism that is microscopic (too small to be seen by the human eye). The study of microorganisms is called microbiology.
..... Click the link for more information.
..... Click the link for more information.
An infection is the detrimental colonization of a host organism by a foreign species. In an infection, the infecting organism seeks to utilize the host's resources to multiply (usually at the expense of the host).
..... Click the link for more information.
..... Click the link for more information.
Arteries are muscular blood vessels that carry blood away from the heart.[1] All arteries, with the exception of the pulmonary and umbilical arteries, carry oxygenated blood.
The circulatory system is extremely important for sustaining life.
..... Click the link for more information.
The circulatory system is extremely important for sustaining life.
..... Click the link for more information.
This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.
Herod_Archelaus
