The upper gastrointestinal tract includes the mouth, esophagus, stomach, and duodenum (also known as the small bowel). This system is essential because it is used by our body to digest food, which is a primary function of life. When food enters the body through the mouth, it is carried by the esophagus to the stomach. The acid in the stomach then churns food into small particles to make them easier to digest. The food particles then enter the duodenum, where bile from the liver and digestive juices from the pancreas react with the food to help the digestive process. Both bile and enzymes are necessary for food digestion. Because the upper gastrointestinal tract serves such an important role in the body, you should address any issues as quickly as possible.