The pleura is a thin, protective tissue that surrounds the lungs and lines the inner chest cavity. As a serous membrane, it secretes fluid that lubricates and cushions the lungs, enabling smooth movement during breathing. This covering is fundamental for respiratory function.
Anatomy and Location
Each lung is encased within a pleural sac, composed of two primary layers: the visceral pleura and the parietal pleura. The visceral pleura is the inner layer, intimately adhering to the surface of the lung and extending into its fissures. It also covers the blood vessels, bronchi, and nerves entering and exiting the lung at the hilum.
The parietal pleura forms the outer layer, lining the internal surfaces of the thoracic cavity. It attaches to the rib cage (costal pleura), the upper diaphragm (diaphragmatic pleura), and the lateral mediastinum (mediastinal pleura), the central chest compartment containing the heart and other structures.
Between these two pleural layers lies a potential space called the pleural cavity. This cavity normally contains a small amount of pleural fluid, typically a few milliliters, which acts as a lubricant. The right and left pleural cavities are distinct and do not connect, which is important in preventing the spread of infection between the lungs.
Role in Respiration
The pleura plays a significant role in facilitating breathing mechanics. The thin layer of pleural fluid within the pleural cavity allows the visceral and parietal pleura to glide smoothly over each other with minimal friction during breathing. This fluid, containing lubricating macromolecules, reduces friction, improving lung compliance.
The pleural fluid creates a surface tension that helps to keep the visceral and parietal pleura in close contact. This adhesion ensures that as the chest wall and diaphragm expand during inspiration, the lungs are pulled along with them, allowing them to inflate and fill with air. The pleural cavity also maintains a negative intrapleural pressure, which is essential for lung expansion and prevents the lungs from collapsing.
Understanding Pleural Space Issues
Disruptions within the pleural space can significantly impact lung function and breathing. Conditions that involve the accumulation of substances in this potential space can compromise the pleura’s ability to facilitate smooth lung movement.
One such condition is pneumothorax, which occurs when air enters the pleural cavity. This air disrupts the negative pressure that normally keeps the lung expanded, leading to a partial or complete collapse of the lung. Another common issue is pleural effusion, characterized by the buildup of excess fluid in the pleural space. Both pneumothorax and pleural effusion can restrict lung expansion, making breathing difficult and often painful.