The Stomach's Contribution to the Digestion System
After food is done in the mouth, it goes down a long channel called the esophagus all the way down your body and into the stomach. The stomach uses many enzymes and muscle contractions in order to break down food particles. The enzymes that are secreted in the stomach are called gastric enzymes. Pepsin is the main gastric enzyme. It is produced by the stomach cells called "chief cells" in its inactive form pepsinogen. Pepsinogen is then activated by the stomach acid (HCl) into its active form, pepsin. Pepsin breaks down protein in food into smaller particles, such as polypeptide fragments and amino acids. Protein digestion first starts in the stomach, unlike carbohydrate and lipids, which start their digestion in the mouth. HCl brings pH below 3 to activate the enzyme converting pepsinogen to pepsin and kills microbes. The optimal pH level in which the stomach enzymes work best is from around 1.5-2.2 which is very acidic.