The Mediastinal pleura is the thin membrane that lines the chest cavity in the area between the lungs.
The pleura is a two-layered structure: the parietal pleura lines the walls of the chest cage and covers the upper surface of the diaphragm, while the pulmonary pleura, or visceral layer, tightly covers the surface of the lungs. The two layers, which are actually one continuous sheet of tissue, are usually connected to each other. In humans, the pleural cavity is further separated into left and right sides by the heart and pericardial cavity. There is normally a slight amount of watery fluid within the pleural cavity that lubricates the pleural surfaces and allows the lungs to slide freely over the inner surface of the thoracic wall during breathing.
When a lung collapses or develops an infection, a condition known as pleurisy can develop. In this condition, the pleura becomes inflamed and the pleural cavity becomes noticeably larger. Pleurisy can be extremely painful, but can usually be taken care of with medicine.
Mesothelioma is another difficulty that can develop with the pleura. It is a tumor seen most frequently in asbestos workers due to the toxicity of that substance.