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Histology - Small & Large Intestine

Histology - Small & Large Intestine

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Small Intestine: General Features
Includes the duodenum, jejunum, and ileum (which can be remembered with the mnemonic Don't Jiggle It)
Wall Layers
  • Mucosa
    • Villi are finger-like extensions of mucosa
    • Covered in surface columnar epithelial cells, including absorptive enterocytes, from which microvilli extend into the lumen as a brush border.
    • Surface epithelium also secretes surface mucus for protection and lubrication.
    • Villi and microvilli increase surface area for absorption
  • Submucosa
    • Separated from mucosa by muscularis mucosae
  • Muscularis externa
    • Longitudinal and circular layers of smooth muscle
    • Innervated by enteric nervous system
  • Serosa
Circular folds, aka, plicae circulares, (aka, folds of Kerkring)
  • Provide increased surface area for digestion. Recall that continued digestion of foods and absorption of nutrients are key functions of the small intestine.
    • Are most prominent in the middle region of the small intestine (largely absent in colon).
Lacteals
  • Lacteals are the lymphatic structures of the small intestine that absorb lipids, and are in close association with the vasculature.
Tubular intestinal glands/crypts
  • Further increase the surface area of the small intestine.
  • Paneth cells, which are not distinguishable here, reside at the base of the crypts; they secrete antimicrobial peptides that protect enterocytes from bacteria.
Goblet cells
  • Secrete lubrication
Small Intestine: Specifics
Brunner's glands in submucosa of duodenum
Peyer's patches
    • Aggregations of lymphoid tissues with a germinal center surrounded by a dome.
Lymphoid tissues are present in all parts of the gastrointestinal tract (except the stomach), and are collectively referred to as GALT – gut-associated lymphoid tissue. Peyer's patches are most prevalent in the distal section of the small intestine and the colon.
COLON
The large intestine includes the colon, which is subdivided per its direction of travel within the abdominopelvic cavity, and the rectum and anus.
Walls
  • Four layers, continuous with those of small intestine
Tubular glands in mucosa
  • Abundant goblet cells
The large intestine is responsible for absorption of water, salt, vitamins and minerals; though not visible in our sample, the glands are deeper than in the small intestine.
Again, remember that the large intestine does not have circular folds.
Images:
Histology (Mark Braun, MD, & Indiana University: http://medsci.indiana.edu/c602web/602/c602web/toc.htm; http://www.indiana.edu/~anat215/virtualscope2/start.htm)
Clinical correlation: Colitis Ulcerative colitis Psedumembranous colitis

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