Mucosa Layers

Expansion

Mucosa (three layers)

1. Epithelium: type varies by site and function
2. Lamina propria: loose connective tissue with capillaries, lymphatics and immune cells
3. Muscularis mucosae: thin smooth muscle producing local folding

Beneath lie the submucosa (denser connective tissue with larger vessels, Meissner plexus, and in some sites glands), the muscularis propria (with Auerbach plexus between its layers), and the serosa or adventitia.

The muscularis mucosae is the critical landmark. Lymphatics are essentially absent in the epithelium and sparse above this layer, so a tumour confined above it has no route for metastasis. This is why:

• Carcinoma in situ and high grade dysplasia can be treated endoscopically
• T1 disease is defined by invasion into the submucosa, at which point nodal spread becomes possible
• Oesophageal and gastric superficial cancers are stratified by depth relative to this layer

Mucosal glands are confined to the mucosa; submucosal glands are found only in the oesophagus and duodenum (Brunner glands), which is a useful identifying feature.