These mechanisms of the gastrointestinal tract (GIT) are up-regulated by the vagus nerve of the parasympathetic nervous system (PNS), which carries out the majority of its functions by the release of neurotransmitter Acetylcholine (Ach), and to a lesser extent gastrin releasing peptide (GRP) protein. On the contrary, the functions of GIT are down-regulated by the activation sympathetic nervous system (SNS), which carries out its functions mostly via neurotransmitter epinephrine.Meal consumption causes distention of the stomach, leading to stimulation of the parasympathetic vagus nerve in the gastric mucosa, which causes the release of GRP protein. In gastrinoma, GRP protein causes larger than normal amounts of gastrin secretion, which leads to hyperplasia of the parietal cells. Hyperplasia of parietal cells causes an abnormal release of HCl into the duodenum, which causes the ulcers of the duodenum. Excessive HCl production also causes hyperperistalsis, a condition marked by excessive rapidity of the passage of food through the stomach and intestine and inhibits the activity of lipase, causing severe fatty diarrhea known as steatorrhea. Evenly the long-standing hyper-secretion of gastrin stimulate proliferation of the enterochromaffin like cells (ECL). These cells are found along the side the gastric lumen of the digestive tract. They play a main role in regulation of gastric secretion and motility when stimulated by nervous system. These cells in return will undergo progressive dysplastic changes starting with hyperplasia to neoplasia throughout the gastrointestinal tract.
They are characterized by gastric hypersecretion that results in peptic ulcers and diarrhea; this condition is known as Zollinger–Ellison syndrome (ZES). Research
Recently, research studies have been conducted to seek new medical advances in relation to gastrinoma and Zollinger–Ellison syndrome. The recent studies have shown improved understanding of pathogenesis of pancreatic neuroendocrine tumors, classifications of those tumors, new treatments/preventions to control the gastrin levels in the gastrointestinal tract, and the best and safest surgical approaches. The study concluded that the wide use of proton pump inhibitors itself might further induce hypergastrinemia (increased gastrin levels in circulatory system) by feedback inhibition. The body will try to induce further release when gastrin level is depleted. Some of the new treatments might include medication that is directed towards the liver such as embolization, chemoembolization, and radioembolization in addition to the currently offered treatments such as chemotherapy, somatostatin analogs. Other treatments that are still in phase three of clinical trials include liver transplantation and peptide-radioreceptor therapy. See also
Pancreatic endocrine tumor

References
External links
Emedicine