The primary function of the pleural membrane is to separate the two lungs in the human body. It provides a barrier to help keep the two lungs away from each other while remaining air tight, so if one lung is punctured or collapses due to an accident, the other pleural cavity will still be air tight, meaning the other lung will still work normally. The medical reasoning behind this is that the parietal pleura are highly sensitive to pain but the visceral pleura are not. This is due to the fact that it has a dual blood supply, from the bronchial and pulmonary arteries. In humans there is not an anatomical connection between the left and right pleural cavities; this means the pneumothorax, which is the other hemithorax will still be able to function normally. Another important function of the pleural membrane is that it makes breathing easier. There are two separate pleural membranes, the inner and outer pleura. The outer pleura is attached to the chest wall and is identified as the Parietal pleura while the inner one is attached to the lung and other visceral tissues and is seen as the Visceral pleura. The pleural cavity is situated between the two pleura and it is filled with fluid produced by the pleura. This fluid lubricates the pleural surface and allows the two layers to slide against each other easily during respiration. This also provides a surface tension that allows the lung surface to keep in contact with the chest wall. During regular gentle breathing, the cavity normally experiences a negative pressure which holds on the lungs to the chest wall, so the movements of the chest wall during breathing are coupled closely to movements of the lungs and this makes breathing easier.
