The mouth, teeth, tongue, and esophagus work to chew food into manageable pieces, passing food into the stomach. Saliva from the salivary glands begins the initial breakdown of food sugars.
The stomach first serves as a holding area for ingested food. Its main purpose is the initial digestion of proteins through acidic and enzymatic secretions. The stomach also secretes a compound that helps the body absorb vitamin B12.
The liver and pancreas are accessory digestive organs. The liver produces bile, which helps the small intestine break down fats. The pancreas secretes a fluid into the small intestine that neutralizes acid from the stomach and provides several important digestive enzymes.
After chyme (a semi-fluid mass of partially digested food) enters the small intestine, digestion of food particles is completed. Afterward, the small intestine walls absorb digested nutrients into the bloodstream and then pass food remains, bacteria, mucus cells, and debris into the large intestine.
The large intestine contains bacteria such as E. coli, which feed on portions of food residue passed from the small intestine. The intestinal wall then absorbs water and electrolytes from the residue and vitamins secreted by the bacteria. The large intestine's main purpose, though, is to push feces out of the body.