The term of lung membranes refers to the pleural membranes, which are two thin layers of tissue that line the lungs and chest cavity. The inner layer is called the visceral pleura and the outer layer is called the parietal pleura. Together, these two layers form a protective barrier between the lungs and the chest wall. The pleural membranes also help to keep the lungs inflated and allow for the exchange of oxygen and carbon dioxide.