The lungs are nestled in a cavity, shielded by the pleura. The pleura, a form of serous membrane, wraps around each lung. This membrane arrangement consists of two layers: the visceral and parietal pleurae. The visceral pleura lines the surface of the lungIn contrast, the parietal pleura is the outer layer and contacts to the thoracic wall, the mediastinum, and the diaphragm. The hilum is the point of connection between the visceral and parietal layers. The space between the parietal and visceral layers is referred to as the pleural cavity.

In addition to their protective function, the pleurae serve two crucial purposes: the production of pleural fluid and the formation of cavities that protect major organs. Mesothelial cells from both pleural layers are responsible for the secretion of the pleural fluid. This fluid lubricates the pleurae surfaces, minimizing friction and preventing damage during respiration. This fluid also creates surface tension, which helps keep the lungs adhered to the thoracic wall, ensuring that the lungs expand as the chest cavity enlarges during inhalation.Furthermore, the pleurae serve to compartmentalize the thoracic cavity, isolating major organs to prevent disruption from organ movement and limiting the spread of infections.

Inflammation to the visceral and parietal pleural membranes, pleurisy or pleuritis, leads to pain due to a friction between these two pleurae. Air, blood, or pus can also sometimes accumulate in the pleural cavities, a condition known as pneumothorax, hemothorax, or pyothorax, respectively. Pneumothorax, often the result of chest surgery or penetrating chest trauma such as a knife or bullet wound, may lead to total lung collapse. The primary treatment aim involves removing air (or blood) from the pleural space to facilitate lung re-expansion. In some cases, a minor pneumothorax may resolve itself; however, the placement of a chest tube is commonly required to aid the evacuation process.