histo - large intestines

7/29/2019 Histo - Large Intestines

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Large Intestine

Dr M Ressam Nazir


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Large Intestine

The large intestine is well suited to its main functions

1.Absorption of water and electrolytes

2.Formation of the fecal massfrom undigestible material3.Production of abundant mucus that lubricates the intestinal

surface.

4.Intestinal bacteria also produce certain vitamins like Vit. K and B12


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MUCOSA (Colon)

Lumen is larger than that of small intestine.

Luminal surface of the mucosa is smooth.

No villi or plicae circulares.

In undistended colon, the mucosa and submucosaexhibit temporary folds.

Epithelium simple columnar with numerous goblet cells.

Intestinal glands

Lamina propria lymphatic nodules extending upto the submucosa

Muscularis mucosae


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Epithelium

Simple columnar epithelium

Short irregular microvilli

Goblet cells

Goblet cells are numerous.

Increase in number towards terminal colon

Mucous secreting cells (unicellular glands)


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Submucosa

Connective tissue cells

and fibers

Blood vessels

Nerves, Meissnersplexus

Lymphocytes and

lymphatic nodules


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Muscularis Externa (Colon)

Two layers of smooth

muscle

1. Inner circular muscle layer

continuous in the colon wall

2. Taeniae coli

outer muscle layer

condensed into three broad,

longitudinal bands

Contractions of taeniae coli

produces haustrations in the

wall of colon


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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

and mesentery)

covers the cecum,transverse colon and

sigmoid colon.

small, pendulous

protuberances of

adipose tissue

(appendices epiploicae)


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Appendix


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Appendix

It is a blind evagination of the

cecum near the beginning oflarge intestine.

Small and irregular lumen

Very Irregular, very few and

widely placed crypts

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


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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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MEDICAL APPLICATION

Appendix is a closed sac and its

contents are relatively static, it can

easily become a site of inflammation

(appendicitis).

With the small lumen and relatively thin

wall of the appendix, inflammation and

the growth of lymphoid follicles in the wallcan produce swelling that can lead to

bursting of the appendix.

Severe appendicitis is a medical

emergency since a burst appendix will

produce infection of the peritoneal 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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Recto-anal junction


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Recto-anal junction (7)

The Key Changes

1. Muscularis mucosae and theintestinal glands terminate (3,4)

2. Lamina propria is replaced by

dense irregular connective tissue(2,9)

3. Submucosa merges with CT in the

lamina propria of anal canal (5,9)

4. Internal hemorrhoidal plexus of

veins lie in the mucosa of anal

canal (10)

5. Muscularis Externa

1. Circular layer increases in

thickness in upper region of

anal canal and forms

internal anal sphincter (6)

2. In lower part it is replaced

by skeletal muscles of

external anal sphincter (12)


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The End

histo - large intestines

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