Human digestive system the esophagus at its upper end and to the duodenum at its lower end. Gastric acid (informally "gastric juice"), produced in the stomach plays a vital role in the digestive process, and mainly contains hydrochloric acid and sodium chloride. A peptide hormone, gastrin, produced by G cells in the gastric glands, stimulates the production of gastric juice which activates the digestive enzymes. Pepsinogen is a precursor enzyme (zymogen) produced by the gastric chief cells, and gastric acid activates this to the enzyme pepsin which begins the digestion of proteins. As these two chemicals would damage the stomach wall, mucus is
Digestive biscuit packs sold annually. Digestives are also popular in food preparation for making into bases for cheesecakes and similar desserts. Chocolate digestive biscuits are also available, coated on the underside with milk, dark or white chocolate. Originally produced by McVitie's in 1925 in the UK as the Chocolate Homewheat Digestive, other varieties include the basic biscuit with chocolate shavings throughout (chocolate "chips" in the biscuit mix), or a layer of caramel, mint chocolate, orange-flavoured chocolate, or plain chocolate. American travel writer Bill Bryson described the chocolate digestive as "a British masterpiece". The McVitie's chocolate digestive is the most popular biscuit in