The small bowel is a tubular organ 3–4 m in length, which starts at the pylorus and terminates at the ileocecal valve . In a recent study, the small bowel length measured from the ligament of Treitz to the ileocecal valve was 2.83–3.45 m . It is usually subdivided into the duodenum, jejunum, and ileum. The most proximal portion is the C-shaped duodenum, approximately 25 cm long, which is almost a fixed retroperitoneal structure. Four subdivisions of the duodenum are recognized: the first or superior portion (bulb, D1); the second or descending portion, which includes the papilla of Vater (D2); the third or horizontal portion (D3); and the fourth or ascending portion (D4). At the duodenojejunal flexure (the so-called ligament of Treitz), which is left of the midline at the level of the second lumbar vertebra, the duodenum becomes continuous with the intra-abdominal small intestine. Just by convention, the jejunum comprises the upper two-fifths of the intraperitoneal small intestine, and the distal three-fifths are designated as the ileum. The multiple intra-abdominal coils are mobile; they are attached to the mesentery (Fig. 19.1). The diameter decreases from about 25 mm in the duodenum to 19 mm in the distal ileum .
KeywordsNormal small intestine Normal small bowel Pylorus Duodenum Gastric heterotopia Brunner’s glands Jejunum Ileum Terminal ileum villi Lymph follicles Ligament of Treitz Kerckring’s folds Papilla Ileocecal valve
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