Mucosa, submucosa, muscularis externa and serosa or adventitia
Mnemonic
“Mucosa, Submucosa, Muscularis, Serosa”, from lumen outwards, with the mucosa itself in three:
- Mucosa - epithelium, lamina propria, muscularis mucosae
- Submucosa - containing Meissner’s (submucosal) plexus and the vessels
- Muscularis propria - inner circular, outer longitudinal, with Auerbach’s (myenteric) plexus between them
- Serosa or adventitia
“Submucosal plexus is in the submucosa; myenteric is between the muscle layers”, and “Meissner secretes, Auerbach moves”, since the submucosal plexus controls secretion and blood flow while the myenteric controls motility.
The stomach adds a third, innermost oblique muscle layer, and the oesophagus has adventitia rather than serosa through most of its course, which is one reason oesophageal tumours spread early.
Expansion
From the lumen outwards:
- Mucosa - epithelium, lamina propria and muscularis mucosae
- Submucosa - connective tissue with vessels, lymphatics and the submucosal (Meissner’s) plexus
- Muscularis externa - inner circular and outer longitudinal muscle, with the myenteric (Auerbach’s) plexus between them
- Serosa (where peritoneum covers) or adventitia (where it does not)
The muscularis mucosae is the critical boundary: a tumour confined above it has essentially no access to lymphatics and therefore no metastatic potential, which is why carcinoma in situ can be treated endoscopically.
T staging then follows the layers: T1 invades submucosa, T2 muscularis propria, T3 beyond into subserosa, T4 through the serosa or into adjacent organs.
The absence of a serosa over most of the oesophagus and the posterior rectum is one reason tumours there spread early.