Histology Fact Sheet: Gastrointestinal System

The gastrointestinal tract is a continuous long tube.  It is is about nine meters long. The basic histology of the wall is similar throughout the entire gastrointestinal tract. However, there are distinguishing characteristics in each region. For example, brunner's glands are found in the duodenum.

When looking at the histology it can be seen that tThe wall of the gastrointestinal tract has four tunics or layers:

• Mucosa
• Submucosa
• Muscular externa
• Serosa or adventitia

Histology slide of the small intestine
Histology slide courtesy of Education Interactive, Histology Photo CD

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Mucosa

The mucosa is the innermost layer of the GI tract.  The mucosa, or mucous membrane layer, lines the lumen of the digestive tract.

In certain regions, the mucosa develops folds that increase the surface area. Certain cells in the mucosa secrete mucus, digestive enzymes, and hormones. Ducts from other glands pass through the mucosa to the lumen.

Gut associated lymphatic tissue (GALT) is found in the mucosa and sometimes extends into the submucosa.

Epithelium

The mucosa consists of a lining epithelium, lamina propria and muscularis mucosa. The epithelium is usually simple columar epithelium.  In the anus, where thickness for protection against abrasion is needed, the epithelium is stratified squamous epithelium. The stomach and intestines have a thin simple columnar epithelium for secretion and absorption.

Lamina Propria

Lying beneath the epithelium is the lamina propria.  This is loose connective tissue.  The lamina propria is part of the mucosa. 

Muscularis Mucosa

When looking at the histology it can be seen that bBeneath the lamina propria is a thin layer of smooth muscle called the muscularis mucosa. Muscularis mucosa is part of the lamina propria.

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Submucosa

The submucosa is a thick layer of loose connective tissue deep to the mucosa. The submucosa is comprised of dense irregular connective tissue. Within the submucosa are blood vessels, lymphatic vessels and nerve plexuses. Meissner's plexus is located in the submucosa.  Glands may also be found in the submucosa.

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Muscularis Externa

The muscularis externa consists of thick layers of smooth muscle. The smooth muscle responsible for movements of the digestive tract.  The muscle is arranged in two layers, an inner circular layer and an outer longitudinal layer. The myenteric plexus of Auerbach is located in the muscularis externa.The myenteric plexus is between the two muscle layers.

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Serosa/Adventitia

The outer layer of the GI tract is either an adventitia or serosa. The serosa consists of only a single layer of epithelial cells (mesothelium) and underlying connective tissue. The adventitia is the outer layer of the GI tract when it is abutting another organ the posterior abdominal wall.

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Sources:

Histology: A Text and Atlas
Michael H. Ross/Edward J. Reith

http://www.training.seer.cancer.gov; funded by the U.S. National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program, via contract number N01-CN-67006, with Emory University, Atlanta SEER Cancer Registry, Atlanta, Georgia, U.S.A.