Where is gastrin produced, and what stimulates its production?

Gastrin is a hormone of peptide origin that is secreted by the G cells in the pyloric antrum of the stomach, the duodenum and the pancreas, as a response to certain stimulus, like meals.

Its main function, is to activate the parietal cells of the stomach in order for them to start producing stomach acids, particularly HCI (hydrochloric acid), in order for digestion of proteins, and other such molecules, to be carried out. Another function of gastrin, aside from accelerating the production of gastric acid, is to stimulate stomach motility to ensure better mixing of the stomach acids with the contents in it for better digestion.

The reasons for why the production of gastrin is stimulated are: when the antrum of the stomach is distended, the presence of partially digested proteins, particularly amino acids, and finally, certain illnesses like hypercalcemia.