large intestine histology

8/2/2019 Large Intestine Histology

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LARGE INTESTINE


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Large Intestine


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Large Intestine

The large intestine is wellsuited to its main functions

1. Absorption of water andelectrolytes *****

2. Formation of the fecalmass from undigestiblematerial,

3.Production of abundantmucus that lubricates theintestinal surface.

4. Intestinal bacteria alsoproduce certain vitaminslike vit. K and B12 *****


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COLON


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COLON and CECUM

The wall of the colon has the same basic layers as thesmall intestine.

1. Mucosa

2. Submucosa

3. Muscularis Externa

4. Serosa/ Adventitis


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MUCOSA ( Colon)

Lumen is larger than that ofsmall intestine.**

Luminal surface of the mucosa issmooth**

No villi or plicae circulares ***** In undistended colon, the

mucosa and submucosa exhibittemporary folds**

Epithelium simple columnar with numerous

goblet cells.** Intestinal glands Lamina propria

lymphatic nodules extending uptothe submucosa

Muscularis mucosae


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Mucosa

Epithelium

Simple columnar epithelium

Colonocytes (absorptive cells)

Short irregular microvilli**

Goblet cells

Goblet cells are numerous.**

Increase in number towards terminalcolon

Mucous secreting cells (unicellularglands)


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Submucosa

Connective tissue cells and fibers

Blood vessels

Nerves, Meissners plexus

Lymphocytes and lymphatic nodules


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Muscularis Externa ( Colon )

Two layers of smooth muscle modified

Inner circular muscle layer continuous in the colon wall,

Taeniae coli *****

outer muscle layer condensed into three broad, longitudinal bands Contractions of taeniae coli produces haustrations in

the wall of colon

Outer longitudinal muscle layer very thin often discontinuous found between the taeniae coli

Myenteric (Auerbachs) nerve plexus parasympathetic ganglion cells Found between the two smooth muscle layers of the

muscularis externa


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Serosa (Colon)

Serosa

(visceral peritoneum andmesentery)

covers the cecum, transverse

colon and sigmoid colon. small, pendulous

protuberances of adiposetissue (appendicesepiploicae)**


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MEDICAL APPLICATION- CANCER

Approximately 9095% of malignant tumors of thedigestive system are derived from gastric or intestinalepithelial cells, usually in the large intestine.

Malignant tumors of the colon are derived almostexclusively from its glandular epithelium(adenocarcinomas) and are the second most commoncause of cancer deaths in the United States.


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Appendix


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Appendix

It is a blind evagination of thececum near the beginning oflarge intestine.

Small and irregular lumen*

Very Irregular, very few andwidely placed crypts**

Few goblet cells**

No taeniae coli.**

It has no function in digestion. It is a significant component of

the MALT, with abundantlymphoid follicles in its wall.


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Appendix

Mucosa Epithelium

Simple columnar Few Goblet cells

Lamina Propria Intestinal glands (Crypts of Liberkhun)

Shorter and less dense tubular glands Lymphatic nodules***

Numerous Germinal centers

Extend upto submucosa

Muscularis mucosae- incomplete

Submucosa Numerous blood vessels Muscularis Externa

Inner rcircular smooth muscles Myenteric plexus

Outer longitudinal smooth muscles No taeniea coli**

Serosa- outermost coat


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Appendix- identification points

Ring of lymph nodules

No taenia coli

Fewer crypts

Indistinct muscularismucosae


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MEDICAL APPLICATION

Appendix is a closed sac and itscontents are relatively static, it caneasily become a site of inflammation(appendicitis).

With the small lumen and relativelythin wall of the appendix,inflammation and the growth oflymphoid follicles in the wall canproduce swelling that can lead to

bursting of the appendix. Severe appendicitis is a medical

emergency since a burst appendixwill produce infection of theperitoneal cavity (peritonitis).


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Rectum


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Rectum Temporary longitudinal folds

(core of submucosa covered by mucosa)

Mucosa

Surface Epithelium

Simple columnar cells

Striated border

Goblet cells

Lamina Propria

Intestinal glands

longer, close together, filled with goblet cells

Adipose cells Lymphatic nodules

Muscularis mucosae


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Rectum

Submucosa

Muscularis Externa

Inner circular

Myenteric plexus ( parasympathetic

ganglia)

Outer longitudinal

No taenia coli**

Adventitia/ Serosa

Adventitia covers a portion of rectum,remaining is covered by serosa


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Recto-anal junction


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Recto-anal junction

Permanent longitudinal folds inlower rectum and anal canal analcolumns of Morgagni***

Depressions b/w the anal columnsare called as anal sinuses.

About two cm above the analopening, at the recto-anal junction,the lining of the mucosa is replacedby stratified squamousepithelium.

In this region, the lamina propriacontains a plexus of large veinsthat, when excessively dilated andvaricose, can producehemorrhoids.**


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Recto-anal junction

Muscularis mucosae and theintestinal glands terminate

Lamina propria is replaced bydense irregular connective tissue

Submucosa merges with CT inthe lamina propria of anal canal

Internal hemorrhoidal plexusof veins lie in the mucosa ofanal canal

Muscularis Externa Circular layer increases in thickness

in upper region of anal canal andforms internal anal sphincter

In lower part it is replaced by skeletal

muscles of external anal sphincter


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Recto-anal junction

large intestine histology

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