Serosa (orserous membrane) is a smooth membrane consisting of a thin layer ofcells, found on the outer wall of theorgans of theabdominal cavity known as the serous cavity. It secretes serous fluid, and a thinconnective tissue layer. They secrete a lubricating fluid whichreduces friction frommuscle movement.
Serosa is not to be confused withadventitia, a connective tissue layer which binds together structures rather than reducing friction between them. The serous membrane covering the heart and lining themediastinum is called thepericardium, the serous membrane lining thethoracic cavity and surrounding the lungs is called the pleura, and that lining theabdominopelvic cavity and the viscera is called theperitoneum.
The portions of the gastrointestinal tract that do not have a serosa include the esophagus, as well as the middle and distal rectum.