Muscularis mucosae
The lamina muscularis mucosae is a thin layer of muscle of the gastrointestinal tract, located outside the lamina propria, and separating it from the submucosa. It is present in a continuous fashion from the esophagus to the upper rectum. A discontinuous muscularis mucosae–like muscle layer is present in the urinary tract, from the renal pelvis to the bladder; as it is discontinuous, it should not be regarded as a true muscularis mucosae.
In the gastrointestinal tract, the term mucosa or mucous membrane refers to the combination of epithelium, lamina propria, and muscularis mucosae. The etymology suggests this, since the Latin names translate to "the mucosa's own special layer" and "muscular layer of the mucosa".
The muscularis mucosae is composed of several thin layers of smooth muscle fibers oriented in different ways which keep the mucosal surface and underlying glands in a constant state of gentle agitation to expel contents of glandular crypts and enhance contact between epithelium and the contents of the lumen.Additional images
