A hormone, produced by G cells in the mucosa of the stomach and first part of the duodenum, that controls the release of gastric juice and stimulates movements of the stomach wall. The secretion of gastrin is stimulated by stretching of the stomach wall due to the presence of food. It is one of the hormones that integrates and controls digestive processes (see also secretin). As gastric juice lowers pH in the stomach, negative feedback tends to inhibit further gastrin secretion.