Most of the activity occurs in the small intestine. Digestion begins in the mouth and continues in the stomach. The actual digestion of the food happens in the small intestine with the help of pancreatic juices and bile juices. About 90% of the nutrients that enter the bloodstream happen here. In the duodenum, the first part of the small intestine, the semi-digested food called chyme mixes with the digestive juices to transform the food into its simplest form.