The digestive system: People need energy to live. The digestive, circulatory, respiratory and excretory systems are responsible for obtaining this energy. The digestive system involves several parts of our body: mouth, esophagus, stomach, small intestine, large intestine and anus. Digestion begins in your mouth. Your teeth break down the food. Your tongue mixes the food with your saliva. Then, the food goes into the stomach through the esophagus. In your stomach, that food mixes with gastric juices. In the small intestine, our body absorbs the nutrients. The unabsorbed waste in the small intestine moves into the large intestine. Here, water and mineral salts are absorbed. The waste is then expelled through the anus.