The small intestine or bowel is part of the digestive tract. It is a long tube (about 30 ft.) that runs from the duodenum (at the outlet from the stomach) to the large intestine. In order to fit into the abdomen, it is wound back and forth within the abdominal cavity. It is where most of the nutrients and water are extracted from food before waste products are excreted. It also separates the digestive bacteria from the bloodstream while being able to pass nutrients to the blood.
There are several diseases, such as colitis, Crohn's disease and irritable bowel syndrome that affect the small intestine. Moreover, any perforation in the bowel will leak contents into the abdominal cavity, causing peritonitis, or the bloodstream, most likely leading to sepsis. Most gunshot victims die from bacteria released by the perforated bowel rather than from any trauma caused by the wound.
The bowel can also suffer blockage, which can be life threatening. Luckily, a large portion of the bowel can be removed and the remaining ends sutured together with very little effect on the patient.