Pathophysiology of Small Intestine
The most important functions of the small intestine are digestion and absorption of nutrients. They are achieved by an interaction between intact small bowel motility and gastrointestinal hormones. Clinically recognizable disturbances of small bowel function arise mainly from alterations in the motor activities or interference with digestion and absorption.
Abdominal pain is a common manifestation of several processes involving the small intestine. The pain is often located in the mid abdomen (periumbilical region) but can also be diffuse across the abdomen. Progressive small bowel distention with or without obstruction causes colicky pain in the early stages, which later becomes constant and unrelenting. Invasive bacteria such as Yersinia can invade the terminal ileum, causing severe pain and tenderness mimicking acute appendicitis. Severe postprandial pain that incites fear of eating (sitophobia) is diagnostic of mesenteric ischemia, especially when it is accompanied by weight loss in an atherosclerotic patient. Crohn disease frequently involves the distal small bowel, with deep transmural ulceration and crampy abdominal pain in the right lower quadrant.