JEJUNUM
Figure 14­55
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Holdings,
The jejunum is the longest segment of the small intestine, extending from the duodenum to ileum. Most of the nu-
trients generated from the digestive process are absorbed by the columnar intestinal epithelial cells (enterocytes)
LLC.
located in this region.
Not
As in other parts of the small intestine, the jejunum exhibits several ways of increasing the area for absorption.
to
Instead of a straight tube, the jejunum is highly coiled. Folds containing elements of the submucosa and mucosa
be
redistributed
called plicae circulares (or valves of Kerckring) enlarge the surface area of the tube. The mucosa evaginates into
the lumen to form villi to add to the absorptive surface. Finally, the enterocytes themselves have microvilli at their
apical surface, which further enhance the absorptive area.
or
The four major components of the wall of the jejunum are shown here. The mucosa (M), consisting of an epithelial
modified
sheet, underlying loose connective tissue of the lamina propria, and the muscularis mucosae, forms the moist mem-
brane lining the lumen. In this image of the jejunum, the submucosa (SB) forms a thin, dense band under the mu-
in
cosa. The inner circular and outer longitudinal layers of smooth muscle constituting the muscularis externa (ME) are
any
shown. Because the jejunum lies within the peritoneal cavity, it is covered by the simple squamous epithelium and
way
small amount of connective tissue forming the serosa (S). The mesenteric connection of the organ is still attached
without
(arrow).
We have divided the small intestine into its three component segments and have described their features separately.
permission.
Although the histologic characteristics of the duodenum allow it to be identified distinctly from the other two regions,
such is not always the case in trying to identify the jejunum from the ileum. There are similarities in structure shared
by the two segments, and there is a gradual transition between the two.
Ideally, one can say that the jejunum has the most elongated villi of any of the three regions of the small intestine,
an intermediate number of goblet cells, an absence of glands in the submucosa, and an absence of Peyer's patches
to distinguish this region from the duodenum and ileum. However, it is not always possible to apply all of these
criteria with assurance.
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