The tissues lining (or covering) the lungs are called the pleura. There are two pleura. These can be called pleural membranes. The gap between them is called the pleural space. The pleura are fibrous sheets. They help to protect the lungs. They produce a lubricating fluid that fills the gap between the two pleura. This helps the lungs to move smoothly in the chest when they are inflating and deflating as we breathe.



Mesothelioma is most often diagnosed in the pleura. This is known as pleural mesothelioma. Because it is so close, pleural mesothelioma can also affect the sheet of tissue covering the heart - the pericardium. Doctors call the pericardium the lining, although it is on the outside of the heart. It protects the heart and allows it to move smoothly within the sac that surrounds it. So it does much the same job for the heart as the pleura do for the lungs.