Gastric acid

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Gastric acid

Gastric acid is one of the main secretion

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....
s of 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....
, together with several 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....
s 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....
. Chemically it is an acid

Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
solution

Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
with a 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 1 to 2 in the stomach lumen

Lumen (anatomy)

A lumen in biology is the inside space of a tubular structure, such as an artery or intestine. By extension, a lumen can also be the inside space of a cellular component or structure, such as the endoplasmic reticulum....
, consisting mainly of hydrochloric 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....
(HCl), and large quantities of potassium chloride

Potassium chloride

The chemical compound potassium chloride is a metal halide Salt 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....
(KCl) and sodium chloride

Sodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the chemical formula SodiumChlorine....
(NaCl).

ric acid is produced by parietal cell

Parietal cell

Parietal cells, or oxyntic cells, are the stomach epithelium cell s that secrete gastric acid and intrinsic factor....
s (also called oxyntic cells) in the stomach.

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Physiology

Gastric acid is produced by parietal cell

Parietal cell

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

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 gastric acid is secreted into the lumen of the stomach. These cells are part of epithelial

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....
fundic glands

Fundic glands

The fundus glands are found in the Body of stomach and Fundus of the stomach.They are simple tubes, two or more of which open into a single duct....
in the gastric mucosa

Gastric mucosa

The gastric mucosa is the mucous membrane layer of the stomach which contains the glands and the gastric pits. In men it is about 1 mm thick and its surface is smooth, soft, and velvety....
. The pH

Proton pump

A proton pump is an integral membrane protein that is capable of moving protons across the cell membrane of a cell , mitochondrion, or other subcellular compartment....
H⁺/K⁺ ATPase

Hydrogen potassium ATPase

Gastric hydrogen potassium ATPase is also known as H+/K+ ATPase...
. The parietal cell releases bicarbonate

Bicarbonate

In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid. Its chemical formula is HCO3−....
into the blood stream in the process, which causes the temporary rise of pH in the blood, known as 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....
.

The resulting highly acidic environment in the stomach lumen 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 lose their characteristic folded structure (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....
). This exposes the protein's 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.The chief cells of the stomach secrete enzymes for protein breakdown (inactive pepsinogen and renin). Gastric acid activates pepsinogen into 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 ....
–this enzyme

Enzyme

Amino acid

In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent....
s, a process known as proteolysis

Proteolysis

Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion....
. In addition, many microorganism

Microorganism

A microorganism or microbe is an organism that is microscopic . The study of microorganisms is called microbiology, a subject that began with Anton van Leeuwenhoek's discovery of microorganisms in 1675, using a microscope of his own design....
s have their growth inhibited by such an acidic environment which is helpful to prevent infection

Infection

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 resources to multiply ....
.

Secretion

Chloride and hydrogen ions are secreted separately from the cytoplasm of parietal cells and mixed in the canaliculi. Gastric acid is then secreted into the lumen of the oxyntic gland and gradually reaches the main stomach lumen.

Chloride and sodium ions are secreted actively from the cytoplasm

Cytoplasm

The cytoplasm is the part of a Cell that is enclosed within the plasma membrane. In eukaryote cells the cytoplasm contains organelles, such as mitochondrion, that are filled with liquid kept separate from the rest of the cytoplasm by biological membranes....
of the parietal cell into the lumen of the canaliculus. This creates a negative potential of -40 mV

Volt

The volt is the SI SI derived unit of electric potential difference or electromotive force, commonly known as voltage. It is named in honor of the Lombard physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery ....
to -70 mV across the parietal cell membrane that causes potassium ions and a small number of sodium ions to diffuse

Diffusion

Molecular diffusion, often called simply diffusion, is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion....
from the cytoplasm into the parietal cell 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....
.

The enzyme 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....
catalyses the reaction between carbon dioxide and water to form carbonic acid

Carbonic acid

Carbonic acid has the Molecular formula H2CO3. It is also a name sometimes given to solutions of carbon dioxide in water , which contain small amounts of H2CO3....
. This acid immediately dissociates into hydrogen and bicarbonate ions. The hydrogen ions leave the cell thru H⁺/K⁺ ATPase

Hydrogen potassium ATPase

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

Antiporter

An antiporter is an integral membrane protein which is involved in secondary active transport of two or more different molecules or ions across a phospholipid membrane such as the plasma membrane in opposite directions....
pumps.

At the same time sodium ions are actively reabsorbed. This means the largest amount of secreted K⁺ and Na⁺ ions return to the cytoplasm. In the canaliculus, secreted hydrogen and chloride ions mix and are secreted into the lumen of the oxyntic gland.

The highest concentration that it reaches in the stomach is 160 mM in the canaliculi. This is about 3 million times that of arterial

Artery

Arteries are blood vessels that carry blood away from the heart. All arteries, with the exception of the pulmonary and umbilical arteries, carry oxygenated blood....
blood

Blood

Blood is a specialized bodily fluid that delivers necessary substances to the body's Cell s ? such as nutrients and oxygen ? and transports waste products away from those same cells....
, but almost exactly isotonic

Isotonic

The term isotonic may refer to;* Isometric exercise and Weight training#Isotonic, Isometric and Plyometric exercises* Isotonic for the term associated with muscle contraction...
with other bodily fluids. The lowest pH of the secreted acid is 0.8, but the acid is diluted in the stomach lumen to a pH between 1 and 3.

There are three phases in the secretion of gastric acid:

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.
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.
The intestinal phase: the remaining 10% of acid is secreted when chyme
Chyme

Chyme is the semifluid mass of partly digested food expelled by the stomach into the duodenum. In other words, chyme is half digested food. Also known as Chymus, it is the liquid substance found in the stomach before passing through the pyloric valve and entering the duodenum....
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

Autonomic nervous system

The autonomic nervous system is the part of the peripheral nervous system that acts as a control system, maintaining human homeostasis in the body....
and several hormone

Hormone

Hormones are chemicals released by cells that affect cells in other parts of the body. Only a small amount of hormone is required to alter cell metabolism....
s. The parasympathetic nervous system

Parasympathetic nervous system

The parasympathetic nervous system is a division of the autonomic nervous system , along with the sympathetic nervous system and enteric nervous system ....
, 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 the hormone 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....
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

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....
from enterochromaffine-like cells (ECL). Vasoactive intestinal peptide

Vasoactive intestinal peptide

Vasoactive intestinal peptide is a peptide hormone containing 28 amino acid residue s and is produced in many areas of the human body including the gut, pancreas and suprachiasmatic nuclei of the hypothalamus in the brain....
, cholecystokinin

Cholecystokinin

Cholecystokinin is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein. Cholecystokinin, previously called pancreozymin, is synthesised by I-cells in the mucosal epithelium of the small intestine and secreted in the duodenum, the first segment of the small intestine, and ca...
, and secretin

Secretin

Secretin is a peptide hormone produced in the S cells of the duodenum in the crypts of Lieberk?hn. Its primary effect is to regulate the pH of the duodenal contents via the control of gastric acid secretion and buffering with bicarbonate....
all inhibit production.

The production of gastric acid in the stomach is tightly regulated by positive regulators and negative feedback

Negative feedback

Negative feedback feeds part of a system's output, inverted, into the system's input; generally with the result that fluctuations are attenuated....
mechanisms. Four types of cells are involved in this process: parietal cells, G cell

G cell

In anatomy, the G cell is a type of cell in the stomach that secretes gastrin. It works in conjunction with gastric chief cells and parietal cells....
s, D cells and enterochromaffine-like cells. Besides this, the endings of the vagus nerve (X) and the intramural nervous plexus in the digestive tract influence the secretion significantly.

Nerve endings in the stomach secrete two stimulatory neurotransmitter

Neurotransmitter

Neurotransmitters are chemistry which relay, amplify and modulate signals between a neuron and another cell . Neurotransmitters are packaged into vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of...
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....
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

Somatostatin

Somatostatin is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G-protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones....
.

Neutralization

In the duodenum

Duodenum

The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum....
, gastric acid is neutralized by sodium bicarbonate

Sodium bicarbonate

Sodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula NaHCO3. Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder....
. This also blocks gastric enzymes that have their optima in the acid range of pH

Pancreas

The pancreas is a gland Organ in the digestive system and endocrine system of vertebrates. It is both an endocrine gland , as well as an exocrine gland, secreting pancreatic juice containing Digestion enzymes that pass to the small intestine....
is stimulated by secretin

Secretin

Secretin is a peptide hormone produced in the S cells of the duodenum in the crypts of Lieberk?hn. Its primary effect is to regulate the pH of the duodenal contents via the control of gastric acid secretion and buffering with bicarbonate....
. This polypeptide hormone gets activated and secreted from so-called S cell

S cell

S cells are cells which release secretin, found in the jejunum and duodenum. They are stimulated by a drop in pH to 4 or below in the small intestine's lumen....
s in the mucosa of the duodenum and jejunum

Jejunum

The jejunum is the middle section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms middle intestine or mid-gut may be used instead of 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

Carbonic acid

Carbonic acid has the Molecular formula H2CO3. It is also a name sometimes given to solutions of carbon dioxide in water , which contain small amounts of H2CO3....
instantly decomposes into 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 water

Water (molecule)

File:Blue-water-pool.jpgWater is the most abundant molecule on Earth's surface, constituting about 70% of the Earth's surface in liquid, solid, and gaseous states....
, then gets eliminated through urine

Urine

Urine is a liquid waste product of the body secreted by the kidneys by a process of filtration from blood called urination and excreted through the urethra....
.

Role in disease

In hypochlorhydria and 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....
, 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
Vibrio

Vibrio is a genus of Gram-negative bacteria possessing a curved rod shape. Typically found in Seawater, Vibrio are Facultative anaerobic organism that test positive for oxidase and do not form spores....
or Helicobacter
Helicobacter

Helicobacter is a genus of Gram-negative bacterium possessing a characteristic helix shape. They were initially considered to be members of the Campylobacter genus, but since 1989 they have been grouped in their own genus....
bacteria).

In Zollinger-Ellison syndrome

Zollinger-Ellison syndrome

Zollinger-Ellison syndrome is a disorder where increased levels of the hormone gastrin are produced, causing the stomach to produce excess hydrochloric acid....
and hypercalcemia, there are increased 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....
levels, leading to excess gastric acid production, which can cause gastric ulcers.

In diseases featuring excess vomiting, patients develop hypochloremic

Chlorine

Chlorine...
metabolic alkalosis

Metabolic alkalosis

Metabolic alkalosis is a metabolic condition in which the pH of the blood is elevated beyond the normal range. This is usually the result of decreased hydrogen ion concentration, leading to increased bicarbonate, or alternatively a direct result of increased bicarbonate concentrations....
(decreased blood acidity by H

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
⁺ and chlorine

Chlorine

Chlorine...
depletion).

Pharmacology

The proton pump enzyme is the target of 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, used to increase gastric pH in diseases which feature excess acid. H₂ antagonists indirectly decrease gastric acid production. Antacid

Antacid

An antacid is any substance, generally a Base or basic salt, which counteracts gastric acid. In other words, antacids are stomach acid neutralization ....
s neutralize existing acid.

Gastric acid

Physiology

Secretion

Regulation of secretion

Neutralization

Role in disease

Pharmacology

See also

External links