Page 590 - Atlas of Histology with Functional Correlations

Paneth cells are located at the base of intestinal glands, characterized by

deep-staining eosinophilic granules in their cytoplasm.

Lymphatic Nodules and Lymphocytic Cells

Peyer patches are aggregations of closely packed, permanent lymphatic

nodules that are found primarily in the wall of the terminal portion of the small
intestine, the ileum. These nodules occupy a large portion of the lamina propria
and submucosa of the ileum. The dispersed lymphocytes and the Peyer patches
constitute the gut-associated lymphoid tissue (GALT) that serves as an
immunologic barrier throughout the gastrointestinal tract.

M cells are specialized epithelial cells that cover the Peyer patches and large
lymphatic nodules; they are not found anywhere else in the intestine. Instead of
microvilli, these cells exhibit numerous apical microfolds, hence the name “M
cells.” M cells phagocytose luminal antigens and transport them to the

lymphocytes and antigen-presenting dendritic cells located in the lamina propria
resulting in adaptive immune responses that produce specific antibodies that are
then transported to the intestinal lumen to eliminate harmful pathogens from its
surface.

Regional Differences in Small Intestine

The duodenum is the shortest segment of the small intestine. Here, the villi are
broad, tall, and numerous, with fewer goblet cells in the epithelium. Branched

duodenal (Brunner) glands with mucus-secreting cells in the submucosa
characterize this region. The glands, however, diminish in number toward the
end of the duodenum.

The jejunum is longer than the duodenum and contains the largest surface

area for the absorption of the digested material. Here, the villi are tall and lined
with simple columnar epithelium composed of absorptive cells and some mucus-
secreting goblet cells. There are also more goblet cells in the epithelium of the
jejunum than in the duodenum. The jejunum does not contain any duodenal
(Brunner) glands or lymphatic nodule aggregations (Peyer patches).

The ileum contains villi that are narrow and short with the epithelium
containing more goblet cells than the duodenum or the jejunum. In addition to
increased numbers of lymphocytes in the lamina propria, the aggregated
lymphatic nodules (Peyer patches) are large and most numerous in the distal

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