The stomach is the primary organ that breaks down food as it enters the digestive system. This organ receives food from the esophagus and eventually directs the partially digested food into the small intestine. It also helps kill harmful bacteria.
The stomach measures roughly 12 inches long and 6 inches wide. It consists of three layers, the innermost of which produces acid that helps break down food into smaller components. The muscles in the stomach aid in mixing the food with acid and enzymes, and these muscles also move food through the stomach. Eventually, the food is mashed into a semi-liquid substance called chyme, at which point it typically enters the small intestine.