The normal biopsy: Mucosa and submucosa

The digestive tract is a hollow tube consisting throughout of three coats or layers. The first layer, the mucosa, is made up of an epithelial lining which borders on the lumen of the bowel and rests upon a basement membrane, the lamina propria and the muscularis mucosae. The second coat is the submucosa. The muscularis propria, the third layer, is composed of two layers of smooth muscle separated by a thin layer of connective tissue in which the ganglionated myenteric plexus (Auerbach's) can be observed. The subserosa is composed of loose areolar tissue covered by mesothelium where the tract borders on the body cavity (serosa). Endoscopic biopsies are limited to the mucosa and upper part of the submucosa. A good understanding of the normal histology of the mucosa and submucosa is essential for analysis of endoscopic biopsies of the colon.