The small intestine plays a key role in digestion and absorption. It consists of the duodenum, jejunum, and ileum. The duodenum receives partially digested food from the stomach along with pancreatic and bile secretions to continue digestion. The jejunum is the primary site of nutrient absorption. The ileum has more goblet cells and lymphoid tissue called Peyer's patches. Villi and crypts lined with absorptive enterocytes aid in digestion and absorption throughout the small intestine.

1. Histology of Intestine
Assoc. Prof. Dr. Karim Al-Jashamy
IMS/MSU 2010

2. 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

3. SMALL INTESTINE
• Plicae circularis
• Villus
• Enterocyte
• Brush border (microvilli)
• Crypts of Lieberkuhn
• Brunner glands (Duodenum)
• Peyer’s patches

4. DUODENUM

6. Subdivisions of the Small Intestine
 Duodenum
 Attached to the stomach
 Curves around the head of the pancreas
 Jejunum
 Attaches anteriorly to the duodenum
 Ileum
 Extends from jejunum to large intestine
Chemical Digestion in the Small Intestine
 Source of enzymes that are mixed with chyme
 Intestinal cells
 Pancreas
 Bile enters from the gall bladder
Slide 14.22

7. 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

8. Chemical Digestion in the Small Intestine
Slide 14.23b

11. Duodenum Histology

12. 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

13. Duodenum - H&E
• 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 cells
throughout the remainder of
the GIT.
• The identify of the lamina
propria, muscularis mucosae
and the "packages" of
glandular tissue (Brunner's
glands) in the connective
tissue between the muscularis
mucosae and muscularis
externa

14. • 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.

15. 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

16. Segments of the Intestine

17. Jejunum - H&E
• identify plicae circulares,
muscularis externa and villi.
• Next identify surface epithelium
(simple columnar with goblet
cells), crypts, muscularis
mucosae, 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

19. •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

20. The Ileum
 The final segment of small intestine
 3.5 meters (11.48 ft) long

22. Crypt

23. ENTEROCYTES

24. Small Int Ileum
The 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)

25. SI Crypts x20

26. SI Ileum Peyer’s Patch x4

27. 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.

28. 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

29. Histology of Large Intestine

30. • 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 muscularis
mucosae 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.

31. • 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 externa
does not aggregate into taenia coli.

34. • Ano-rectal junction, human -
van Gieson
Identify 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.