From the esophagus, we get to the stomach, where more mechanical digestion happens (the stomach churns and moves around to further break down food) and more chemical digestion occurs simultaneously. The stomach secretes gastric juices to help break apart the food further and into the nutrients we need that get absorbed later on in the digestive system. The movement of food within the stomach is called segmentation; it’s the mixing motion that basically sloshes food around haha. Within the stomach, we have gastric pits that hold important cells which provide different things to the stomach. Parietal cells are found in the gastric pits, and they secrete hydrogen ions (Hydrochloric acid) that enters the lumen of the stomach to acidify the content. We also have chief cells that secrete an enzyme called pepsinogen that becomes pepsin and helps breakdown proteins. Pepsinogen starts off as a pro enzyme, which is an enzyme that is not yet active, into the stomach. Pepsinogen is then activated by the low pH in the gut and becomes pepsin. Pepsin is what breaks down the proteins found in the stomach. There are also surface epithelial cells that produce a thick coating of mucus, which protects the gastric mucosa from acid and enzymes. Surface epithelial cells also secrete bicarbonate.
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