bowel
Summary
The bowel (intestines) includes the small intestine (duodenum, jejunum, ileum) and large intestine (colon, rectum, anal canal). The small bowel is primary site of nutrient absorption; the colon absorbs water and electrolytes.
Detail
The gastrointestinal tract from the pylorus to the anus is divided into small and large intestine. The small intestine (6-7 meters long) is composed of the duodenum (site of acid neutralization, bile/pancreatic enzyme entry, iron absorption), jejunum (primary nutrient absorption site), and ileum (vitamin B12 and terminal ileum absorbs bile acids, important for their reabsorption). The large intestine (1.5 meters) consists of the colon and rectum, where water and electrolyte reabsorption occurs and fecal matter is stored. The bowel wall has four layers: mucosa (epithelium + lamina propria + muscularis mucosae), submucosa, muscularis propria (circular + longitudinal muscle), and serosa/adventitia. Peristalsis is coordinated by intrinsic and extrinsic innervation (parasympathetic via vagus increases motility; sympathetic decreases motility). Common board topics include malabsorption syndromes, inflammatory bowel disease, irritable bowel syndrome, and obstruction.
Sources
- First Aid for USMLE Step 1
- Harrison's Principles of Internal Medicine
- Robbins Pathology
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