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Small bowel (small intestine)

Normal histology


Reviewer: Hanni Gulwani, M.D. (see Reviewers page)
Revised: 8 November 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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Layers:
● Mucosa, submucosa, muscularis propria (externa), subserosa, serosa

Mucosa:
● Contains villi with central blood vessels, lymphatics
● Layers are epithelium, lamina propria, muscularis mucosa

Villi:
● Short and stubby in duodenum, very tall in jejunum, intermediate height in ileum
● Contain microvilli
● Villus to crypt length is 3-5:1
● Lined by primarily columnar absorptive cells and goblet cells
● Usually 1 lymphocyte per 5 enterocytes
● Villi may be short and distorted next to lymphoid aggregates
● 4 normal villi in a row in a biopsy suggests normal villous architecture
● Each villus contains an arteriole with capillary network, veins and a central lymphatic with numerous nerve fibres

Absorptive cells:
● Have microvilli on luminal surface (brush border) and underlying mat of microfilaments (terminal web)

Microvillus:
● 1.5 to 2 µm in length and 100 nm in diameter
● PAS positive, actin-myosin complexes

Goblet cells:
● Occur in crypts and surface absorptive cells
● Decrease towards villus tip, increase in frequency along small intestine (most numerous in lower ileum)
● Columnar in shape, mucus droplet in supranuclear area, secretes mucus, ions and water

Crypts of Lieberkuhn:
● Lower 20% of epithelium, contain undifferentiated (immature) crypt cells, Paneth cells (have large, apical eosinophilic granules containing antimicrobial proteins), scattered goblet cells and endocrine cells
● Are surrounded by pericrypt fibroblast sheath
● Secrete ions, water, IgA, antimicrobial peptides into lumen
● Crypt cells take 3-8 days to migrate to surface
● Allows for rapid repair, but also causes these cells to be sensitive to radiation therapy and chemotherapy

Lamina propria:
● Contains loose connective tissue, lymphocytes, plasma cells, occasional eosinophils, macrophages, mast cells, neutrophils

Submucosa:
● Contains connective tissue, blood vessels, lymphatics, submucosal (Meissner’s) plexus
● Also Brunner’s glands in duodenum

Brunner glands:
● Submucosal mucous glands in duodenum, secrete bicarbonate ions, glycoproteins, pepsinogen II
● Resemble gastric pylorus mucous glands

Muscularis propria (externa):
● Inner circular and outer longitudinal layer, with myenteric (Auerbach’s) plexus between these layers
● Plexus also contains interstitial cells of Cajal (Am J Surg Pathol 2003;27:228), ganglion cells, fibroblasts

Serosa:
● Contains mesothelial lining, loose connective tissue

Endocrine cells:
● Similar to cells in pancreas, biliary tree, lung, thyroid, urethra
● Contain fine eosinophilic granules with secretory proteins
● Nuclei on luminal side of granules, not basal

Micro images
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Brunner glands


Crypts of Lieberkuhn


Enterocyte


Serosa


Villi



Duodenum


Jejunum

End of Small bowel (small intestine) > Normal histology


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