Small intestine & ampulla

General

Histology-small intestine



Last author update: 20 January 2022
Last staff update: 20 January 2022

Copyright: 2003-2022, PathologyOutlines.com, Inc.

PubMed Search: Histology[TI] small bowel[TIAB]

Kenechukwu Ojukwu, M.D., M.P.P.
Danielle Hutchings, M.D.
Page views in 2021: 13,372
Page views in 2022 to date: 17,877
Cite this page: Ojukwu K, Hutchings D. Histology-small intestine. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/smallbowelnormalhistology.html. Accessed December 7th, 2022.
Definition / general
  • Extends from gastric pylorus to ileocecal valve
  • Layers include mucosa, submucosa, muscularis propria (externa), subserosa and serosa (described luminal to external)
  • Functions relies on the structure of mucosal villi and crypts, lined by columnar cells
Essential features
  • Extends from gastric pylorus to ileocecal valve
  • Composed of duodenum, jejunum and ileum
  • Layers include mucosa, submucosa, muscularis propria (externa), subserosa and serosa (described luminal to external)
  • Villi lined by columnar absorptive cells and goblet cells
  • Crypts comprise the lower portion of mucosa and contain Paneth cells, endocrine cells and undifferentiated (immature) crypt cells
Terminology
  • Small bowel
  • Duodenum, jejunum, ileum
Physiology
  • Villi are the location for digestion and absorption of food into the columnar cells (Gastrointest Endosc Clin N Am 2017;27:1)
  • Crypts secrete ions and water and deliver IgA and antimicrobial peptides to the lumen
  • Cell division and renewal occur in crypts
  • Mucous cells generate adherent mucous layer that protects the epithelium and allows uptake of nutrients
  • Terminal ileum absorbs intrinsic factor vitamin B12 complexes
Gross description
  • Small intestine is approximately 6 - 7 m in length (Gastrointest Endosc Clin N Am 2017;27:1)
  • Duodenum:
    • Retroperitoneal, except for first part
    • Common bile duct and pancreatic duct enter the second part of the duodenum at the ampulla of Vater
    • Suspensory duodenal ligament (ligament of Treitz) divides duodenum from jejunum
  • Jejunum and ileum:
    • Intraperitoneal
    • Transition between the jejunum and ileum is not clearly defined
    • Wall of jejunum is thicker due to prominent circular mucosal folds (folds of Kerckring / plicae circulares) (Gastrointest Endosc Clin N Am 2017;27:1)
  • Small intestine ends at the ileocecal valve
Gross images

Contributed by Danielle Hutchings, M.D.
Jejunum

Jejunum

Microscopic (histologic) description
  • Mucosa:
    • Contains villi (finger-like projections) with central blood vessels, lymphatics
    • Layers are epithelium, lamina propria and muscularis mucosa
  • Villi:
    • Tallest in the jejunum, may be shorter or show more variability in height in duodenum
    • Surface lined by microvilli
    • Villus to crypt length ratio is 3 - 5:1
    • Lined by primarily columnar absorptive cells and goblet cells
    • Scattered intraepithelial lymphocytes (T cells), usually 1 lymphocyte per 5 enterocytes
    • Villi may be shorter and distorted next to lymphoid aggregates
    • In a biopsy, 4 normal villi in a row suggests normal villous architecture
    • Each villus contains an arteriole with capillary network, veins and a central lymphatic with numerous nerve fibers
  • Absorptive cells:
    • Enterocytes
    • Microvilli on luminal surface (brush border) and underlying mat of microfilaments (terminal web)
  • Microvillus:
    • 1.5 - 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
  • Paneth cells:
    • Populate crypt bases and increase in number from proximal to distal intestine
    • Strongly eosinophilic, pyramidal cells with zymogenic or secretory cell characteristics
    • Supranuclear Golgi complex contains large, chunky apical membrane bound eosinophilic granules
    • Granules contain various proteins involved in host defenses including lysozyme, secretory phospholipase A2 and alpha defensins / cryptdins (World J Gastrointest Pathophysiol 2017;8:150)
  • Crypts of Lieberkühn:
    • Lower 20% of epithelium, contain undifferentiated (immature) crypt cells, Paneth cells, scattered goblet cells and endocrine cells
    • 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 and mast cells
  • Submucosa:
    • Contains connective tissue, blood vessels, lymphatics, submucosal (Meissner) plexus
    • Brunner 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) plexus between these layers
    • Plexus also contains interstitial cells of Cajal, ganglion cells, fibroblasts (Am J Surg Pathol 2003;27:228)
  • Serosa:
    • Contains mesothelial lining, loose connective tissue
  • Endocrine cells:
    • Contain fine eosinophilic granules with secretory proteins
    • Cytoplasmic granules are subnuclear (versus supranuclear granules in Paneth cells)
  • Peyer patch:
    • Lymphoid aggregates randomly distributed around circumference of the small intestine (partially mucosal, partially submucosal) with central germinal center
    • Peyer patch germinal centers are more common in children than adults
    • Increase in number distally in the small bowel and become confluent in the ileum
    • Exogenous dark brown granular pigment may be present within macrophages (Hum Pathol 1987;18:50, Gut 1996;38:390)
Microscopic (histologic) images

Contributed by Danielle Hutchings, M.D.
Layers of small intestine

Layers of small intestine

Villi

Villi

Paneth cells

Paneth cells

Brunner glands

Brunner glands


Peyer Patches

Peyer Patches

Submucosa

Submucosa

Muscularis propria

Muscularis propria

Microvilli and goblet cells

Microvilli and goblet cells

Negative stains
Electron microscopy description
  • Each microvillus contains a core bundle of vertically oriented, polarized actin filaments extending from the tip of the microvillus to the base of the terminal web
Electron microscopy images

Images hosted on other servers:

Microvillus of small intestine

Videos

Small intestine: histology

Board review style question #1

What is the location and function of the submucosal mucous glands shown above?

  1. Duodenum, secrete bicarbonate ions, glycoproteins, pepsinogen II
  2. Duodenum, secrete proteins involved in host defense (e.g. alpha defensins / cryptdins)
  3. Ileum, secrete proteins involved in host defense (e.g. alpha defensins / cryptdins)
  4. Jejunum, secrete bicarbonate ions, glycoproteins, pepsinogen II
Board review style answer #1
A. Duodenum, secrete bicarbonate ions, glycoproteins, pepsinogen II. Brunner glands are located in the duodenum and secrete bicarbonate ions, glycoproteins and pepsinogen II.

Comment Here

Reference: Histology - small intestine
Board review style question #2
Resection of what segment of the small intestine puts the patient at risk for vitamin B12 malabsorption?

  1. First part of the duodenum
  2. Ileum
  3. Jejunum
  4. Second part of the duodenum
Board review style answer #2
B. Ileum. In the ileum, surface epithelial cells, specific receptors are present to uptake intrinsic factor vitamin B12 complexes.

Comment Here

Reference: Histology - small intestine
Back to top
Image 01 Image 02