Gastrinomas are gastrin-releasing tumours in the pancreas and small intestine. Gastrin normally circulates in the blood, causing the stomach to secrete enough acid needed for digestion. If exposed to too much gastrin, the stomach releases excess acid, leading to the formation of severe ulcers in the stomach and small intestine. Too much gastrin can also cause serious diarrhoea. The ulcers caused by gastrinomas are much more dangerous than typical stomach or intestinal ulcers; left untreated, they can cause rupture of the stomach or intestine and even death.