29.0 GI: INTESTINE AND ANAL REGION
a) Define and use properly the following words: Small intestine, Duodenum, Jejunum,
Ileum, Villi, Simple columnar with microvilli, Enterocytes, Crypts of Lieberkuhn, Brush
border, Digestive enzymes, Goblet cells, Argentaffin cells, Stem cells (crypt cells),
Paneth cells, Lamina propria, Smooth muscle, Lymphatics, Central lacteal, Triglycerides,
Lymphoid tissue, Peyer's patches, Lymphoid nodules, Submucosa, Meissner's plexus,
Enteric nervous system , Parasympathetic nerve, Nerve cell bodies, Brunner's glands
(submucosal glands), Compound tubular gland, Muscularis externa, Inner circular, Outer
longitudinal, Large intestine, Appendix, Cecum, Colon, Mucous cells, Rectum, Anus,
Anal glands, Sweat glands, Circumanal glands, Anal sacs.
b) Describe and associate basic structure/function for the following: all structures listed
above.
c) Identify by microscopy: Small intestine, Duodenum, Jejunum, Ileum, Villi, Simple
columnar with microvilli, Enterocytes, Crypts of Lieberkuhn, Brush border, Goblet cells,
Argentaffin cells, Stem cells (crypt cells), Lamina propria, Smooth muscle, Lymphatics,
Central lacteal, Lymphoid tissue, Peyer's patches, Lymphoid nodules, Submucosa,
Meissner's plexus, Enteric nervous system, Parasympathetic nerve, Nerve cell bodies,
Brunner's glands (submucosal glands), Compound tubular gland, Muscularis externa,
Inner circular, Outer longitudinal, Large intestine, Cecum, Colon, Mucous cells, Rectum,
Anus, Anal glands, Sweat glands, Circumanal glands, Anal sacs.
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GI: INTESTINE AND ANAL REGION
I.
ANATOMY
1. Small intestine
a. Duodenum; segment of the intestine that is attached to the stomach.
b. Jejunum; longest segment of the intestine.
c. Ileum joins to the cecum and colon.
2. different regions of the small intestine cannot be easily distinguished histologically
3. The small intestine leads into the large intestine, which leads into the rectum, and the
rectum attaches to the anal region.
II.
UNIQUE STRUCTURAL FEATURES OF SMALL INTESTINE MUCOSA.
1. Villi consisting of surface epithelium and a lamina propria core.
a. Project from the surface.
b. Epithelium is simple columnar with microvilli.
i. They are called enterocytes.
ii. Enterocytes tend to stain darker than epithelial cells lining the pyloric
stomach.
iii. The villi are one of the characteristic features of the small intestine.
iv. The villi tend to have a serrated appearance.
2. Crypts of Lieberkuhn (intestinal glands).
a. Located at the termination of the villi.
b. Extend into the lamina propria.
III.
SURFACE EPITHELIUM.
1. Absorbing cells (enterocytes).
a. The major cell present
b. Tall columnar epithelium with a brush border.
i. Brush border has digestive enzymes that breakdown digested material.
c. They will absorb amino acids, fat, and carbohydrates.
d. Absorption occurs by different means.
i. Passive diffusion.
ii. Facilitated diffusion.
iii. Active transport.
e. Destruction of these cells results in malabsorption and diarrhea.
2. Goblet cells
a. Differ from respiratory tract “mucous cells”;
i. secrete mucus, of a different composition from the respiratory tract
mucous cell
ii. here the secretion is more lipid
b. The small intestine has fewer goblet cells than the large intestine. The cells
secrete “mucus”.
3. Argentaffin cells
a. you do not need to identify
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IV.
CRYPT EPITHELIUM
1. Crypts extend from the base of the villi into the lamina propria.
2. Stem cells (crypt cells)
a. Give rise to the goblet and enterocyte cells
b. proliferate here and move up the villus
c. Rapid turnover of the cells of the villus; thus a lot of cell division and
differentiation
3. Argentaffin cells (you do not need to identify)
4. Paneth cells (you do not need to identify)
V.
LAMINA PROPRIA
1. Loose connective tissue; it surrounds the glands:
2. forms a core of villi.
3. Contains smooth muscle cells
a. helps the villi to move in the lumen.
4. Contains blood vessels, lymphatics
a. central lacteal plays an integral role in absorbing long chain triglycerides
5. Numerous white blood cells are present
6. Extensive lymphoid tissue;
a. helps to filter out foreign particles from the digested material.
7. Peyer's patches
a. Collection of 5-7 lymphoid nodules
b. Usually seen in the ileum.
c. They can bulge into the submucosa.
VI.
SUBMUCOSA
1. Meissner's plexus
a. Part of the enteric nervous system
i. parasympathetic nerve
b. Nerve cell bodies
2. Brunner's glands (submucosal glands)
a. Compound tubular gland
b. Since they are tortuous, will see cross sections.
c. Predominantly in the duodenum (but may extend into jejunum).
d. Series of ducts that terminate on the surface.
e. Can be mucus, serous, or mixed.
VII.
MUSCULARIS EXTERNA
1. Inner circular layer.
a. To mix the luminal content
2. Outer longitudinal layer
a. To propel the luminal content along the tract
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VIII.
FUNCTION OF THE SMALL INTESTINE.
1. Digestion and absorption.
2. Endocrine role.
IX.
LARGE INTESTINE.
1. Consists of the appendix, cecum, colon, and rectum.
a. Can't distinguish histologically the different regions.
2. Mucosa
a. Villi are NOT present.
b. Crypt of Lieberkuhn is deeper than in small intestine.
c. Increased proportion of Goblet cells (20-30%).
i. One characteristic feature to differentiate it from the small intestine or
stomach.
ii. Increased number of goblet cells, as one moves distally
d. Simple columnar epithelium lining it.
e. The lamina propria contains a large amount of lymphatic tissue.
i. Won't have huge aggregates.
ii. Get focal lymphatic tissue.
f. Muscularis externa
3. Terminal region
a. Epithelium becomes stratified squamous at the anal-rectum junction.
b. Epithelium becomes keratinized near the anal opening.
c. Species differences
i. Anal columns, glands, and anal sacs are present in some species.
4. Function
a. Not absorptive because there are no villi.
b. Plays an integral role in water reabsorption.
c. Produces mucus.
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