Histology of Intestine

Assoc. Prof. Dr. Karim Al-JashamyIMS/MSU 2010

Small Intestine• The small intestine is the site of terminal food

digestion, nutrient absorption, and endocrine

secretion.

• The processes of digestion are completed in the

small intestine, where the nutrients (products of

digestion) are absorbed by cells of the epithelial

lining.

• The small intestine is relatively long—

approximately 5 m—and consists of three

segments: the duodenum, jejunum, and ileum.

These segments have many characteristics

SMALL INTESTINE

• Plicae circularis

• Villus

• Enterocyte

• Brush border (microvilli)

• Crypts of Lieberkuhn

• Brunner glands (Duodenum)

• Peyer’s patches

DUODENUM

Subdivisions of the Small Intestine

Slide 14.22

Duodenum

Attached to the stomach

Curves around the head of the pancreas

Jejunum

Attaches anteriorly to the duodenum

Ileum

Extends from jejunum to large intestineChemical Digestion in the Small Intestine

Source of enzymes that are mixed with chyme

Intestinal cells

Pancreas

Bile enters from the gall bladder

The Small Intestine• Plays key role in digestion and absorption of nutrients

• 90% of nutrient absorption occurs in the small intestine

The Duodenum The segment of small intestine closest to stomach

25 cm (10 in.) long

―Mixing bowl‖ that receives:

• chyme from stomach (Mixture of secretions and food in the

stomach)

• digestive secretions from pancreas and liver

• To neutralize acids before they can damage the absorptive

surfaces of the small intestine

Chemical Digestion in the Small Intestine

Slide 14.23b

Duodenum Histology

Intestinal Villi• A series of fingerlike

projections:

– in mucosa of small

intestine

• Covered by simple

columnar epithelium:

– covered with microvilli

• Intestinal Glands

• Goblet cells between

columnar epithelial cells

• Eject mucins onto

intestinal surfaces

• In the epithelium lining, the villi and crypts of the duodenum, and note the absence of plicae circulares.

• The tall columnar epithelium composed of enterocytes, goblet cells and endocrine cellsthroughout the remainder of the GIT.

• The identify of the lamina propria, muscularis mucosaeand the "packages" of glandular tissue (Brunner's glands) in the connective tissue between the muscularismucosae and muscularisexterna

Duodenum - H&E

• Occasionally can see

ducts of Brunner's gland

which penetrate the

muscularis mucosae and

ascend through the

lamina propria.

• Note that goblet cells are

absent from these ducts.

•

Not be able to identify

endocrine cells in the

H&E stained sections.

The Jejunum

• Is the middle segment of small intestine

• 2.5 meters (8.2 ft) long

• Is the location of most:

– chemical digestion

– nutrient absorption

Segments of the Intestine

• identify plicae circulares, muscularis externa and villi.

• Next identify surface epithelium (simple columnar with goblet cells), crypts, muscularismucosae, submucosa and muscularis externa.

• Crypts will probably be small, short and narrow.

• The connection of the crypt with the lumen of the intestine will not always be visible in the plane of the section.

Plicae circulares

• Transverse folds in intestinal lining, permanent features

Jejunum - H&E

•Accumulations of lymphocytes are

common in the mucosa of the GIT, and

they occur frequently in the small

intestine.

•These specialized parts of the small

intestine are called Peyer's patches

The Ileum

The final segment of small intestine

3.5 meters (11.48 ft) long

Crypt

ENTEROCYTES

Small Int IleumThe ileum has proportionally more goblet cells . Its proportion of goblet

cells generally increases as one progresses down the GI tract,

The ileum also displays an increase in the amount of mucosal lymphoid

tissue, which forms conspicuous clusters of lymph nodules, called

Peyer's patches.

The lymphoid tissue of Peyer's patches may bulge out toward the lumen,

displacing villi, and inward across the muscularis mucosae into the

submucosa.

The epithelium overlying this lymphoid tissue is cuboidal (rather than

columnar as on villi).

These structures, together with other more diffuse lymphoid tissue,

constitute the Gut-Associated Lymphoid Tissues, or GALT.

For more on GALT (or, more generally, MALT for Mucosa-Associated

Lymphoid Tissues)

SI Crypts x20

SI Ileum Peyer’s Patch x4

The Colon

• Mucosa with crypts (glands)

• Glands consist of absorptive cells and

mucus secreting cells

• Muscularis propria is very pronounced

• Longitudinal muscle occurs in 3 bands

(taeniae coli) rather than completely

surrounding tract.

Large Intestine: Microscopic Anatomy

• Colon mucosa is simple columnar epithelium except in the

anal canal

• Has numerous deep crypts lined with goblet cells

• Anal canal mucosa is stratified squamous epithelium

• Anal sinuses exude mucus and compress feces

• Superficial venous plexuses are associated with the anal

canal

• Inflammation of these veins results in itchy varicosities

called hemorrhoids

Histology of Large Intestine

• Colon

• Bundles of longitudinal muscle should be clearly visible on the outside of the colon.

• Plicae circulares are absent from the luminal side of the colon.

• Villi are absent and the crypts appear deeper than the ones you observed in the small intestine.

• Goblet cells are numerous.

• The lamina propria and muscularismucosae may be difficult to distinguish.

• Note also that a thin layer of longitudinal muscle is found between the taenia coli on the outside of the inner circular muscle layer.

• The vermiform appendix • is a small blind-ending diverticulum

from the cecum.

• The most important features of the appendix is the thickening of its wall, which is mainly due to large accumulations of lymphoid tissue in the lamina propria and submucosa.

• Intestinal villi are usually absent, and crypts do not occur as frequently as in the colon.

• There is often fatty tissue in the submucosa.

• The muscularis externa is thinner than in the remainder of the large intestine and, the outer, longitudinal smooth muscle layer of the muscularis externadoes not aggregate into taenia coli.

• Ano-rectal junction, human -van GiesonIdentify in this or another section which contains a junction of two parts of the alimentary canal

• glands are typically not visible in "regular" stomach sections.

• Note that the tubules of the glands branch and that they are lined by an almost homogenous population of mucus-producing cells.