CG cell is visible near bottom left, and gastrin is labeled as the two black arrows leading from it. The Human Genome Organisation (HUGO is an organization involved in the Human Genome Project, a project about mapping the human genome The Mouse Genome Informatics (MGI website is run by The Jackson Laboratory. HomoloGene, a tool of the National Center for Biotechnology Information (NCBI is a system for automated detection of homologs (similarity attributable to descent The Entrez Global Query Cross-Database Search System is a powerful Federated search engine or Web portal that allows users to search many discrete Health sciences Ensembl is a joint scientific project between the European Bioinformatics Institute and the Wellcome Trust Sanger Institute, which was launched in 1999 in response to the imminent UniProt is the uni versal prot ein resource a central repository of Protein data created by combining Swiss-Prot, TrEMBL PubMed is a free search engine for accessing the MEDLINE database of citations and abstracts of biomedical research articles In Anatomy, the G cell is a type of cell in the stomach that secretes Gastrin.

In humans, gastrin is a hormone that stimulates secretion of gastric acid by the parietal cells of the stomach. Hormones (from Greek ὁρμή - "impetus" are chemicals released by cells that affect cells in other parts of the body Gastric acid is one of the main Secretions of the Stomach, together with several Enzymes and Intrinsic factor. Parietal cells (also called oxyntic cells) are the Stomach Epithelium cells that secrete Gastric acid and Intrinsic factor In Human anatomy, the stomach is a J-shaped hollow muscular organ of the Gastrointestinal tract involved in the second phase of Digestion, following It is released by G cells in the stomach and duodenum. In Anatomy, the G cell is a type of cell in the stomach that secretes Gastrin. In Anatomy of the Digestive system, the duodenum is a hollow jointed tube about 25-30 cm (10-12 in long connecting the Stomach to the Jejunum Its existence was first suggested in 1905 by the British physiologist John Sydney Edkins,^[1][2] and gastrins were isolated in 1964 by Gregory and Tracy in Liverpool. Liverpool ( is a City and Metropolitan borough of Merseyside, England along the eastern side of the Mersey Estuary ^[3]

Physiology

Genetics

The GAS gene is located on the long arm of the seventeenth chromosome (17q21). Chromosome 17 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome ^[4]

Synthesis

Gastrin is a linear peptide hormone produced by G cells of the duodenum and in the pyloric antrum of the stomach. Peptide hormones are a class of peptides that are secreted into the blood stream and have Endocrine functions in living animals In Anatomy, the G cell is a type of cell in the stomach that secretes Gastrin. In Biology, " Antrum " is a general term for a cavity or chamber which may have specific meaning in reference to certain organs or sites in the body In Human anatomy, the stomach is a J-shaped hollow muscular organ of the Gastrointestinal tract involved in the second phase of Digestion, following It is secreted into the bloodstream. Gastrin is found primarily in three forms:

• gastrin-34 ("big gastrin")
• gastrin-17 ("little gastrin")
• gastrin-14 ("minigastrin")

The numbers refer to the amino acid count. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this

Release

Gastrin is released in response to certain stimuli. These include:

• stomach distension
• vagal stimulation (mediated by the neurocrine bombesin, or GRP in the human)
• the presence of partially digested proteins especially amino acids
• hypercalcemia

Gastrin release is inhibited by:

• The presence of acid (primarily the secreted HCl) in the stomach (a case of negative feedback). The vagus nerve (ˈveɪˌgəs (VĀ-gəs (also called pneumogastric nerve or cranial nerve X) is the tenth of twelve paired Cranial nerves, and is the Bombesin is a 14 Amino acid Peptide originally isolated from the Skin of a Frog. Gastrin-releasing peptide, also known as GRP, is a human Gene. Digestion is the breaking down of chemicals in the body into a form that can be absorbed Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Hypercalcaemia (in American English '''Hypercalcemia''' is an elevated calcium level in the Blood. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are Negative Feedback feeds part of a System 's output inverted into the system's input generally with the result that fluctuations are attenuated
• Somatostatin also inhibits the release of gastrin, along with secretin, GIP(gastroinhibitory peptide), VIP, glucagon and calcitonin. Somatostatin (also known as growth hormone inhibiting hormone ( GHIH) or somatotropin release-inhibiting factor ( SRIF) is a Peptide hormone Secretin is a Peptide hormone produced in the S cells of the Duodenum in the Crypts of Lieberkühn. Gastroinhibitory polypeptide s or Gastroinhibitory peptides (GIP are physiologically important in potentiating Insulin release Glucagon is an important Hormone involved in Carbohydrate metabolism. Calcitonin is a 32-amino acid linear polypeptide Hormone that is produced in Humans primarily by the parafollicular (also known as C-cells of the

Function

The presence of gastrin stimulates parietal cells of the stomach to secrete hydrochloric acid (HCl)/gastric acid. Parietal cells (also called oxyntic cells) are the Stomach Epithelium cells that secrete Gastric acid and Intrinsic factor Secretion is the process of segregating elaborating and releasing chemicals from a cell, or a secreted Chemical substance or amount of substance Hydrochloric acid is the Solution of Hydrogen chloride ( H[[Chlorine Cl]] in water This is done indirectly via binding onto CCK2/gastrin receptors on ECL cells in the stomach, which then responds by releasing histamine, which in turn acts in a paracrine manner on parietal cells stimulating them to secrete H+ ions. Enterochromaffin-like cells or ECL cells are a type of Neuroendocrine cells found in the gastric glands of the Gastric mucosa beneath the Epithelium Histamine is a Biogenic amine involved in local immune responses as well as regulating physiological function in the gut and acting as a Neurotransmitter This is the major stimulus for acid secretion by ECL cells.

Direct binding of gastrin to the parietal cells is involved in parietal cell maturation and fundal growth.

Gastrin also causes chief cells to secrete pepsinogen, the zymogen (inactive) form of the digestive enzyme pepsin. A Gastric chief cell (or peptic cell, or gastric zymogenic cell) is a cell in the Stomach that releases Pepsinogen, gastric lipase and Pepsin is a digestive Protease ( released by the chief cells in the Stomach that functions to degrade food Proteins into A zymogen (or proenzyme) is an inactive Enzyme precursor. A zymogen requires a biochemical change (such as a Hydrolysis reaction revealing the Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Pepsin is a digestive Protease ( released by the chief cells in the Stomach that functions to degrade food Proteins into Pepsinogen is converted to pepsin in a low pH environment, and the HCl provides a suitable environment for its activity. pH is the measure of the acidity or alkalinity of a Solution. It can also increase antral muscle mobility and trophic effect on GI tract and causes promotion of contraction of circular muscle of the stomach. In digestion, gastrin strengthens the antral contractions against the pylorus, and constricts the pyloric sphincter, which has the effect of slowing the rate of gastric emptying.

Gastrin has also been shown to induce production of pancreatic enzymes by acinar cells. The pancreas is a Gland organ in the digestive and Endocrine system of Vertebrates.

It increases gastric blood flow.

Factors influencing secretion

Gastric lumen:

• Stimulatory factors: dietary protein and amino acids, hypercalcemia. Hypercalcaemia (in American English '''Hypercalcemia''' is an elevated calcium level in the Blood. (i. e. during the gastric phase)
• Inhibitory factor: acidity (pH below 3) - a negative feedback mechanism, exerted via the release of somatostatin from δ cells in the stomach, which inhibits gastrin and histamine release. Delta cells (δ-cells or D cells are Somatostatin producing cells They can be found in the Stomach, Intestine and the Islets of Langerhans

Paracrine:

• Stimulatory factor: bombesin
• Inhibitory factor: somatostatin - acts on somatostatin-2 receptors on G cells. Bombesin is a 14 Amino acid Peptide originally isolated from the Skin of a Frog. Somatostatin (also known as growth hormone inhibiting hormone ( GHIH) or somatotropin release-inhibiting factor ( SRIF) is a Peptide hormone in a paracrine manner via local diffusion in the intercellular spaces, but also systemically through its release into the local mucosal blood circulation; it inhibits acid secretion by acting on parietal cells.

Nervous:

• Stimulatory factors: Beta-adrenergic agents, cholinergic agents, gastrin-releasing peptide (GRP)

Circulation:

• Stimulatory factor: epinephrine
• Inhibitory factors:gastric inhibitory peptide (GIP), secretin, somatostatin, glucagon, calcitonin

Role in disease

In the Zollinger-Ellison syndrome, gastrin is produced at excessive levels, often by a gastrinoma (gastrin-producing tumor, mostly benign) of the pyloric antrum or the pancreas. A receptor is cholinergic if it uses Acetylcholine as its Neurotransmitter. Gastrin-releasing peptide, also known as GRP, is a human Gene. Gastric inhibitory polypeptide ( GIP) also known as the glucose-dependent insulinotropic peptide is a member of the secretin family of Hormones Secretin is a Peptide hormone produced in the S cells of the Duodenum in the Crypts of Lieberkühn. Somatostatin (also known as growth hormone inhibiting hormone ( GHIH) or somatotropin release-inhibiting factor ( SRIF) is a Peptide hormone Glucagon is an important Hormone involved in Carbohydrate metabolism. Calcitonin is a 32-amino acid linear polypeptide Hormone that is produced in Humans primarily by the parafollicular (also known as C-cells of the Zollinger-Ellison syndrome is a disorder where increased levels of the hormone Gastrin are produced causing the Stomach to produce excess Hydrochloric acid A gastrinoma is a Tumor that secretes Gastrin. It is frequently the source of the gastrin in Zollinger-Ellison syndrome. Pyloric antrum ( antrum, lesser cul-de-sac) is the initial portion of the pyloric part of the Stomach. The pancreas is a Gland organ in the digestive and Endocrine system of Vertebrates. To investigate for hypergastrinemia (high blood levels of gastrin), a "pentagastrin test" can be performed.

In autoimmune gastritis, the immune system attacks the parietal cells leading to hypochlorhydria (low stomach acidity). Gastritis is an inflammation of the lining of the stomach There are many possible causes Parietal cells (also called oxyntic cells) are the Stomach Epithelium cells that secrete Gastric acid and Intrinsic factor Achlorhydria and hypochlorhydria refer to states where the production of Gastric acid in the Stomach is absent or low respectively This results in an elevated gastrin level in an attempt to compensate for low acidity. Eventually, all the parietal cells are lost and achlorhydria results leading to a loss of negative feedback on gastrin secretion. Achlorhydria and hypochlorhydria refer to states where the production of Gastric acid in the Stomach is absent or low respectively Negative Feedback feeds part of a System 's output inverted into the system's input generally with the result that fluctuations are attenuated

References

Further reading

External links

• Overview at colostate.edu
• Physiology at MCG 6/6ch4/s6ch4_14