Small Intestine
Author: Dr. R. Menaka
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The intestinal wall consists of...
1. Tunica mucosa
2. Tunica submucosa
3. Tunica muscularis
4. Tunica serosa
1. Tunica mucosa
The tunica mucosa divided into the following layers
i. Lamina epithelium- The surface epithelium is simple and consists of columnar and goblet cells. These simple columnar cells of free surface shows striation. The columnar cells actively participate in the absorptive processes. The goblet cells usually occurs singly and present between the columnar cells. They contain varying amount of mucin. These cells protects the intestinal mucosa against mechanical irritation and noxious effects of the enzymes.
ii. Lamina propria- has a supporting framework of reticular tissue with elastic fibers and smooth muscle bundles. The crypts of Lieburhn are simple tubular glands and tightly packed in the lamina propria. These glands secretes mucus and several enzymes. The epithelium of the gland presents Paneth cells and enterochromaffine cells.
iii. Lamina muscularis- consists of bundles of smooth muscle fibers In certain areas, lamina muscularis may also be interrupted by peyer's patches (Gut associated lympoid nodules).
2. Tunica Submucosa
Form of loose connective tissue and elastic fibers network. The duodenal glands (Brunner's gland) are distributed in the submucosa. The Brunner's glands do not extend the full length of the duodenum in sheep, goats and carnivores, where as in horses, cattle and pigs these glands extend into jejunum.
3. Tunica Muscularis
In all species, the tunica muscularis made up of smooth muscle fibers which are arranged an inner circular layer and outer longitudinal layer. The connective tissue between the two muscle layers contains the mesenteric plexus.
4. Tunica Serosa
A serosa covers the entire small intestine. It consists of a layer of loose connective tissue covered by mesothelium.
Note: Histologically the various regions of the small intestine in the domestic animals are not clearly defined.