An organ system of the body is the digestive system, and three organs within this system are the stomach, small intestine and large intestine. These structures all play crucial roles in the overall digestion of the food we eat. The purpose of digestion is to break down our food into small enough particles that they can be absorbed into our cells. Nutrients are then broken apart to release energy stored within them, so that the energy can be used to fuel our cells. The stomach is an expandable sac into which our food moves after we chew and swallow. Very strong and acidic gastric juices are released into the stomach, causing the digestion of proteins and fats. From here, the partially digested food moves into the small intestine. In its first segment, digestion is completed. In the second segment of the small intestine, nutrients are absorbed through its wall and move into the bloodstream. In the large intestine, excess water is reabsorbed and undigested food matter is changed into feces, which will be excreted from the body.