The pleura membrane surrounds the lungs. Similar to the pericardial membrane and pericardial cavity, the pleura is a double membrane with a cavity in be-tween (Figure 10.9). The layer in close contact with the lungs is the visceral pleura.
The other layer lines the thoracic cavity, diaphragm, and the mediastinum (other than the hilus) and is known as the parietalpleura. A good analogy of the pleural cavity anatomyis to think of the lung as a fist being pushed into a balloon partly filled with air. The layer of the balloon close to the fist would be the equivalent to the visceral pleura; the other layer, the parietal pleura. The space between the layers, the pleural cavity, is filled with some fluid (pleural fluid) rather than air as in the balloon. The pleural fluid provides lubrication and minimizes friction when the lungs move during breathing.