Page 590 - Atlas of Histology with Functional Correlations
P. 590

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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