Gastrin is produced by G cells in the pylorus and the duodenum. Gastrin stimulates the secretion of both parietal and chief cells. It causes the gastric glands to increase their secretory activity and stimulates gastric motility. Saliva, food, and gastric juice are mixed together in the stomach to form chyme. The stomach serves as a reservoir for food before release into small intestine. Gastric juice is secreted into the lumen of the stomach. Gastrin is secreted into the bloodstream.