Muscularis mucosae
Lamina muscularis mucosae
The muscularis mucosae is a thin layer of smooth muscle at the deep border of the mucosa, separating it from the submucosa. It produces small local movements of the mucosa.
Overview
The layer usually has an inner circular and an outer longitudinal sheet of smooth muscle, controlled mainly by the submucosal plexus. Its contractions change the folding of the mucosa, increasing contact with luminal contents. They squeeze secretions out of the gastric glands and intestinal crypts. Strands extending into the villi shorten them rhythmically, which helps pump lymph out of the lacteals.
The muscularis mucosae is an important pathological landmark. Carcinoma confined above it is intramucosal, with a very low risk of metastasis, because lymphatics are sparse in the colonic lamina propria. Invasion through it into the submucosa defines invasive carcinoma.
- Location
Deepest layer of the mucosa throughout the alimentary canal. It is absent or rudimentary in the oral cavity and gallbladder.
Anatomy
- Histology
Two thin layers of smooth muscle (inner circular, outer longitudinal) beneath the bases of the glands and crypts.
Function
- Local movements of the mucosa and villi.
- Helps expel glandular secretions.
- Pumps lymph from the lacteals.
Clinical significance
Invasive vs intramucosal carcinoma
Breach of the muscularis mucosae marks the step from high-grade dysplasia or intramucosal carcinoma to invasive (T1) cancer. It decides between endoscopic and surgical treatment.
Compiled from standard anatomy and physiology references — see the Digestive System sources. For education only; not medical advice.