Small Intestine

Ernest H. Rosenbaum, MD 
Adapted for the Canadian edition by Hartley Stern, MD 

The small intestine is the longest segment of the gastrointestinal tract, making up three quarters of its total length. Yet malignant tumors are much less common in this organ than they are in the esophagus, stomach and large bowel. Of all the gastrointestinal tumors diagnosed, only 1.5 percent are found in the small intestine. Fewer than 50 new cases of and about 10 to 15 deaths from cancer of the small intestine are seen annually in Canada. Most patients are over 45, and 60 percent are men.
    There are many reasons for the lower incidence. Cancer-causing agents have less contact with the surface membranes because of the rapid transit time of food through the small bowel compared with the colon. And, since the stool is still liquid, there is less mechanical injury to the membranes.
    The inner surface of the small intestine secretes a large amount of gamma globulin that protects the lining against disease. Benzpyrene hydrolase, which can detoxify carcinogens, is found in large amounts in the lining (mucosa) of the small intestine. Finally, the contents of the small bowel are alkaline, which reduces the production of carcinogens from bile and prevents the formation of nitrosamines, environmental carcinogens that are formed only under acidic conditions.