The stomach acts as a reservoir for food, allowing only small portions to pass into the duodenum at a time. When food reaches the stomach, the hormone gastrin is secreted, stimulating cells in the stomach lining to produce hydrochloric acid. The stomach contents become a thin, liquid porridge that mixes with gastric juice so that proteins can be broken down. Gastric juice contains digestive enzymes, hydrochloric acid, and mucus.
Hydrochloric acid creates an acidic environment in the stomach, which is necessary for the activation of the enzyme pepsin, which breaks down protein.
The enzyme is secreted in the form of pepsinogen, which is activated into pepsin by the action of hydrochloric acid. Hydrochloric acid creates an acidic environment that promotes the action of pepsin and kills most bacteria that are sensitive to acidic conditions.
The mucus protects the stomach lining from acid and bacteria. At the same time, the stomach secretes gastric juice. It contracts and mixes food and gastric juice while the contents are slowly pushed toward the duodenum.
A high-carbohydrate meal leaves the stomach within a few hours, a high-protein meal takes longer, and a high-fat meal remains in the stomach for several hours. The reason for this is that the stomach adjusts its activity based on what it releases into the duodenum.
Feel free to take your own notes.