How does the GI system process food?

Digestive enzymes in the mouth, stomach and small intestine break down ingested food, which is then absorbed into the bloodstream through the small intestine. Fiber proceeds undigested through the intestinal tract, and is processed by bacteria in the large intestine.

When a person takes a bite of food, the process of chewing breaks down food particles, while enzymes in the mouth begin chemical digestion. Muscles in the esophagus propel food to the stomach, where hydrochloric acid digests food particles, and stomach muscles churn these particles into a uniform mixture. As this continues, small amounts of food are allowed into the small intestine through the pylori valve.

The upper part of the small intestine uses enzymes and other chemicals to process food molecules, and virtually all nutrients are absorbed through the walls of the intestine into the bloodstream. Most of the water is also absorbed in the small intestine, leaving only 10% of water to be absorbed by the large intestine. Resident bacteria in the large intestine, called normal flora, ferment the remaining food particles, breaking down indigestible components like fiber. Finally, solid waste is expelled through the anus.