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In the gastrointestinal tract, the submucosa is the layer of dense irregular connective tissue or loose connective tissue that supports the mucosa, as well as joins the mucosa to the bulk of overlying smooth muscle (fibers running circularly within layer of longitudinal muscle).
Blood vessels, lymphatic vessels, and nerves (all supplying the mucosa) will run through here. Tiny parasympathetic ganglia are scattered around forming the submucosal plexus (or "Meissner's plexus") where preganglionic parasympathetic neurons synapse with postganglionic nerve fibers that supply the muscularis mucosae. Histologically, the wall of the alimentary canal shows four distinct layers (from the lumen moving out): mucosa, submucosa, muscularis externa, and a serosa or adventitia.
Identification of the submucosa plays an important role in diagnostic and therapeutic endoscopy, where special fibre-optic cameras are used to perform procedures on the gastrointestinal tract. Abnormalities of the submucosa, such as gastrointestinal stromal tumors, usually show integrity of the mucosal surface.
The submucosa is also identified in endoscopic ultrasound to identify the depth of tumours and to identify other abnormalities. An injection of dye, saline, or epinephrine into the submucosa is imperative in the safe removal of certain polyps.
Endoscopic mucosal resection involves removal of the mucosal layer, and in order to be done safely, a submucosal injection of dye is performed to ensure integrity at the beginning of the procedure.
Small intestinal submucosa
Small intestinal submucosa (SIS) is submucosal tissue in the small intestines of vertebrates. SIS is harvested (typically from pigs) for transplanted structural material in several clinical applications, typically biologic meshes. They have low immunogenicity. Some uses under investigation include a scaffold for intervertebral disc regeneration.
Section of the human esophagus. Moderately magnified.
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