Gastrin
|
|
In humans, gastrin is a hormone that stimulates secretion of gastric acid by the stomach. It is released by G cells in the stomach.
| Contents |
Physiology
Genetics
The GAS gene is located on the long arm of the seventh chromosome (17q21).
Synthesis and release
Gastrin is a linear peptide hormone produced by G cells that are located mainly in the antrum of the stomach and the D cells of the pancreatic islets. It is secreted into the bloodstream. Gastrin is found primarily in three forms: gastrin-34 ("big gastrin"), gastrin-17 ("little gastrin"), and gastrin-14 ("minigastrin"). The numbers refer to the amino acid count.
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 and hypercalcemia. Gastrin release is inhibited by the presence of acid (primarily the secreted HCl) in the stomach (a case of negative feedback). Somatostatin also inhibits the release of gastrin, along with secretin, GIP, VIP, glucagon and calcitonin.
Function
The presence of gastrin stimulates parietal cells of the stomach to secrete hydrochloric acid (HCl). It also causes chief cells to secrete pepsinogen, the zymogen (inactive) form of the digestive enzyme pepsin. Pepsinogen is converted to pepsin in a the low pH environment, and the HCl provides a suitable environment for its activity.
The secretion of gastrin are inhibited by the action of somatostatin released by D cells.
Gastrin has also been shown in induce production of pancreatic enzymes by acinar cells.
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 antrum or the pancreas. To investigate for hypergastrinemia (high blood levels of gastrin), a "pentagastrin test" can be performed.