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JEJUNUM

The jejunum has a median external diameter of 4 cm and an internal diameter of 2.5 cm. It has a thicker wall than the ileum, and an extensive arterial blood supply that makes it appear redder than the ileum in the living. The plicae circulares are most pronounced in the proximal jejunum, where they are more numerous and deeper than elsewhere in the small bowel (Fig. 66.5A). They frequently ‘branch’ around the lumen and may appear to be ranged one on top of another, giving the jejunum a characteristic appearance during single contrast radiography (Fig. 66.6). Lymphoid aggregates are almost absent from the proximal jejunum, but are present distally, although they are fewer in number and smaller than in the ileum. Where present, they are usually discoid in shape and impalpable.

  

Fig. 66.5  Typical cross sections through the proximal jejunum (A) and terminal ileum (B). The mesenteric attachment is wider in the jejunum, and two leaves of vessels enter the bowel wall. The latter is also thicker in the jejunum.

  

Fig. 66.6  Barium studies of the jejunum and ileum. A, Barium follow-through. The feathery appearance of the small intestine is due to the plicae circulares and is most prominent in the jejunum. The constrictions are the result of peristalsis. B, Small bowel enema (enteroclysis). The plicae circulares are clearly demonstrated by this technique. C, caecum; I, ileum; J, jejunum; PC, plicae circulares; TI, terminal part of ileum.

In the supine position the jejunum usually occupies the upper left infracolic compartment, extending down to the umbilical region. The first one or two loops often occupy a recess between the left part of the transverse mesocolon and the left kidney. On supine radiological examination, the jejunal loops are characteristically situated in the upper abdomen, to the left of the midline, whereas the ileal loops tend to lie in the lower right part of the abdomen and pelvis. This distribution can be reversed during paralytic ileus or small bowel obstruction due to rotation around the mesenteric attachment following bowel distension.

Jejunal feeding

In situations where the stomach and duodenum are either unsuitable or unavailable for receiving oral nutrition, delivery of prepared feed to the jejunum is possible using either a surgically created jejunostomy or by insertion of a feeding tube. Because the jejunum is highly mobile, it is possible to bring the first or second loop of jejunum into contact with the abdominal wall to create a surgical jejunostomy. Insertion of a fine-bore feeding tube via the nose as far as the jejunum is also possible: the end of the feeding tube must lie beyond the duodenojejunal flexure to prevent reflux of the feed into the duodenum and stomach, and this is usually confirmed by radiological monitoring of the progress of the tube through the duodenum.

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