The pleura is the serous membrane, which lines the walls of the pulmonary cavities and lungs. It is composed of a single layer of mesothelial cells. The pleura is divided into two areas including the visceral pleura, which envelops the lungs, and the partial pleura, which surrounds the thorax, diaphragm and chest wall. A minimal amount of fluid separates the two layers of pleura, thus allowing smooth movement of the lung within the chest cavity.
In Our Own Words
The pleura is a thin, delicate membrane that lines the wall of the chest cavity and the lungs. There are two pleura areas: The outer pleura lines the walls of the chest cavity and the diaphragm (i.e., a muscle located in the chest that assists with breathing). The inner pleura is also called the visceral pleura and lines the lungs.
In between the two pleura areas is a small amount of fluid. This fluid acts as a lubricant to help the lungs move smoothly in the chest. This movement permits the lungs to expand and contract during breathing. When the pleural area contains more than the small amounts of lubricative fluid needed, this is referred to as a pleural effusion.