Question

Churns and mixes food to a liquid mass (chyme). 3 layers of muscle. Movement of food controlled by cardiac sphincter (into stomach) and pyloric valve (into small intestine). Adds HCL, enzymes, and fluid (gastric juice). Where most protein digestion happens. About 1-2 hours.

Answer 1

The human stomach is critical for protein digestion with the enzyme pepsin and an acidic environment aiding the process. Mechanical digestion occurs through the stomach's churning, producing chyme, with the pyloric sphincter controlling its movement into the small intestine.

Step-by-step explanation:

The subject in question is the human stomach, which is a paramount digestive organ for protein digestion. Within the stomach, the enzyme pepsin plays a vital role in breaking down proteins into smaller polypeptides. This enzyme is secreted by the chief cells in an inactive form known as pepsinogen. When exposed to the highly acidic contents of the stomach, particularly hydrochloric acid produced by parietal cells, pepsinogen is activated into pepsin. This acidic environment also serves to incapacitate many microorganisms present in the consumed food.

Mechanical digestion in the stomach is achieved through the contraction and relaxation of the stomach muscles, resulting in a mixing and churning action that further breaks down the food and mixes it with gastric juices to form chyme. The cardiac sphincter controls the entry of food into the stomach from the esophagus, while the pyloric sphincter regulates the release of chyme into the small intestine for further digestion and absorption of nutrients. After approximately 1-2 hours in the stomach, this partly digested food moves on in a controlled manner, ensuring optimal digestion and absorption downstream in the small intestine.