Gastrin is a hormone that is produced by ‘G’ cells in the lining of the stomach and upper small intestine. During a meal, gastrin stimulates the stomach to release gastric acid. This allows the stomach to break down proteins swallowed as food and absorb certain vitamins. It also acts as a disinfectant and kills most of the bacteria that enter the stomach with food, minimising the risk of infection within the gut.
Additionally, gastrin can stimulate the gallbladder to empty its store of bile and the pancreas to secrete enzymes. Bile and pancreatic enzymes help absorb food in the small intestine.
Gastrin also stimulates growth of the stomach lining and increases the muscle contractions of the gut to aid digestion.
Before a meal, the anticipation of eating stimulates nerves within the brain which signal to the stomach and stimulate the release of gastrin. Gastrin release is also stimulated by the stretching of the stomach walls during a meal, the presence of certain foods (particularly proteins) within the stomach cavity and an increase in the pH levels of the stomach (i.e. the stomach becoming less acidic).
The production and release of gastrin is slowed by the hormone somatostatin, which is released when the stomach empties at the end of a meal and when the pH of the stomach becomes too acidic.
An excess of gastrin can occur due to a gastrin-secreting tumour (gastrinoma, also known as Zollinger-Ellison syndrome) occurring within the small intestine (specifically within the upper part known as a duodenum) or in the pancreas. In gastrinomas, high levels of gastrin moving around the gut stimulate acid release, leading to stomach and small intestine ulcers that may burst. High levels of stomach acid can also cause diarrhoea because the lining of the small intestine becomes damaged.
High levels of circulating gastrin can also occur when the pH of the stomach is high (i.e. not acidic enough), for example, in pernicious anaemia or atrophic gastritis when the stomach lining is damaged and unable to produce and release acid, and during treatment with antacid drugs.
As gastrin also stimulates growth of the stomach lining, it is thought that high gastrin levels may play a role in the development of certain cancers of the digestive tract. However, this has not been proven.
It is rare to have too little gastrin. However, low levels of gastric acid may increase the risk of infection within the gut and may limit the ability of the stomach to absorb nutrients.
Last reviewed: Feb 2018