The mouth is where food enters the body (hopefully). We chew the food to break it into smaller pieces for swallowing. Our saliva contains enzymes which aid the process. The sole purpose of this stage is to make the food small enough that we can swallow it. This is called ingestion. Eating is ingestion.
It is important to note the distinction between ingestion and digestion. Ingestion describes the process of food entering the GI Tract. Digestion describes the conversion of food into a form our bodies can process and how it passes into our bloodstream.
Once swallowed, the food travels down the throat and into the stomach. The stomach stores the food while it is broken down into small digestible pieces. The presence of food triggers the release of gastric acid and other enzymes. The acid also helps to kill any bacteria that may have hitchhiked on the food. As with the mouth, the food isn’t digested in the stomach, only broken down into smaller pieces in preparation for digestion.
This process takes about an hour. Once the stomach is finished, the food has become a thick liquid called chyme (yum!) and the stomach passes the chyme onto the small intestine.