Submucosa

Submucosa is a layer of tissue found in the walls of many tubular organs, most notably the gastrointestinal tract, located between the mucosa and the muscularis externa. It consists of loose to dense connective tissue rich in collagen and elastic fibers, with embedded blood vessels, lymphatics, and nerves. The submucosa also contains glands in certain regions and a network of nerves known as the submucosal nerve plexus (Meissner’s plexus), which is part of the enteric nervous system and regulates vascular tone, glandular secretions, and the activity of the muscularis mucosae.

In the gastrointestinal tract, the submucosa provides vascular and lymphatic support to the mucosa and allows some mobility of the mucosa relative to the muscular layers. The muscularis mucosae, a thin layer of smooth muscle, lies just internal to the submucosa and is controlled in part by the submucosal plexus.

Glandular elements vary by region. In the esophagus, submucosal glands (esophageal glands) may be present to secrete mucus. In the duodenum, Brunner’s glands are located in the submucosa and secrete alkaline mucus to protect the mucosa from gastric acid. Lymphoid tissue such as Peyer’s patches may extend into the submucosa of parts of the small intestine.

Clinical notes: the submucosa is a focus in procedures like endoscopic submucosal dissection, which relies on lifting the mucosa away from this layer. Inflammation or tumors can involve the submucosa, and various submucosal tumors can arise within or beneath this layer.