submucosa

The submucosa is a layer of dense irregular connective tissue found beneath the mucosa in hollow organs throughout the body, including the gastrointestinal tract, respiratory tract, and urinary bladder. It provides structural support and connects the mucosa to the underlying muscle layers.

The submucosa contains blood vessels, lymphatic vessels, nerve fibers (including Meissner's plexus in the gut), and in some regions, glands. In the small intestine, Brunner's glands are located in the submucosa and secrete alkaline mucus.

In the intestines, the submucosa houses Meissner's submucosal nerve plexus, which regulates local secretion and blood flow. It also provides the structural scaffold through which nutrients absorbed by the mucosa access the circulatory and lymphatic systems.