high in viscosity. Stomach The enzymes that are secreted in the stomach are gastric enzymes. The stomach plays a major role in digestion, both in a mechanical sense by mixing and crushing the food, and also in an enzymatic sense, by digesting it. The following are enzymes produced by the stomach and their respective function: Pepsin is the main gastric enzyme. It is produced by the stomach cells called "chief cells" in its inactive form pepsinogen, which is a zymogen. Pepsinogen is then activated by the stomach acid into its active form, pepsin. Pepsin breaks down the protein in the food into smaller particles, such as peptide fragments and amino acids. Protein digestion, therefore, primarily starts in the stomach, unlike carbohydrate and lipids, which start their digestion in the mouth (however, trace amounts of the enzyme kallikrein, which catabolises certain protein, is found in saliva in the mouth). Gastric lipase: Gastric lipase is an acidic lipase secreted by the gastric chief cells in the fundic mucosa of the stomach. It has a pH level of 3–6. Gastric lipase, together with lingual lipase, comprise the two acidic lipases. These lipases, unlike alkaline lipases (such as pancreatic lipase), do not require bile acid or colipase for optimal enzymatic activity. Acidic lipases make up 30% of lipid hydrolysis occurring during digestion in the human adult, with gastric lipase contributing the most of the two acidic lipases. In neonates, acidic lipases are much more important, providing up to 50% of total lipolytic activity. Cathepsin F: This is a digestive enzyme of parasitic flukes. Hormones or compounds produced by the stomach and their respective function: Hydrochloric acid (HCl): This is in essence positively charged hydrogen atoms (H+), or in lay-terms stomach acid, and is produced by the cells of the stomach called parietal cells. HCl mainly functions to denature the proteins ingested, to destroy any bacteria or virus that remains in the food, and also to activate pepsinogen into pepsin. Intrinsic factor (IF): Intrinsic factor is produced by the parietal cells of the stomach. Vitamin B12 (Vit. B12) is an important vitamin that requires assistance for absorption in terminal ileum. Initially in the saliva, haptocorrin secreted by salivary glands binds Vit. B, creating a Vit. B12-Haptocorrin complex. The purpose of this complex is to protect Vitamin B12 from hydrochloric acid produced in the stomach. Once the stomach content exits the stomach into the duodenum, haptocorrin