The gut wall has four layers: the serous layer, the muscular layer, the submucosa, and the mucosa. The outermost layer, the serous, is connective tissue, and the muscular layer is responsible for the movement that keeps food progressing through the GI tract. The mucosal and submucosal layers finish out the final layers. Together, these parts have been termed “the mucosal barrier”—the part of the gut that gets leaky.
