The pleura is a thin membrane that plays a significant role in the respiratory system. It surrounds each lung and lines the inner chest cavity, ensuring the lungs move smoothly during breathing and facilitating comfortable respiration.
Anatomy of the Pleura
The pleura consists of two layers, forming a closed sac around each lung. The inner layer, the visceral pleura, directly covers the lung surface, extending into the fissures that divide the lung lobes. This layer is thin and delicate, closely adhering to the lung tissue. The outer layer, the parietal pleura, lines the inside of the chest wall, the top of the diaphragm, and the sides of the mediastinum, the central chest compartment.
Between these two pleural layers lies a narrow space called the pleural cavity. This space contains a small amount of serous fluid, secreted by the pleura, which provides lubrication. The arrangement of these layers and the fluid-filled cavity is key to the pleura’s function.
Key Functions of the Pleura
The pleura performs several functions for efficient respiration. The pleural fluid acts as a lubricant, reducing friction between the visceral and parietal pleura as they slide past each other during breathing. This allows for smooth expansion and contraction of the lungs within the chest cavity.
Beyond lubrication, the pleural fluid contributes to surface tension, creating an adhesive force. The slight negative pressure within the pleural cavity, combined with the fluid’s surface tension, keeps the lung surfaces closely apposed to the chest wall. This adhesion ensures that when the chest wall expands during inhalation, the lungs are pulled along, allowing them to inflate fully. This mechanism supports proper lung expansion and efficient gas exchange.
The pleura also provides compartmentalization, as each lung is enclosed within its own pleural sac. This separation prevents the spread of infection or disease from one lung to the other. If one lung is compromised, the other can continue to function independently. This compartmentalization also offers protection, shielding the lung tissue from direct physical trauma.
When Pleural Function is Impaired
When the pleura’s normal function is disrupted, it can impact breathing and cause discomfort. One such condition is pleurisy, also known as pleuritis, which involves inflammation of the pleural membranes. This inflammation causes the normally smooth surfaces of the pleura to become rough, resulting in sharp chest pain that worsens with deep breathing, coughing, or sneezing as the inflamed layers rub against each other.
Another common impairment is pleural effusion, characterized by an abnormal accumulation of fluid in the pleural cavity. While a small amount of fluid is normal, too much can compress the lung, making it difficult for it to expand fully during inhalation. This can lead to symptoms such as shortness of breath and chest pain.
Pneumothorax occurs when air leaks into the pleural cavity, either from the lung or from outside the chest. This air buildup creates pressure on the lung, which can cause it to partially or completely collapse. The presence of air disrupts the negative pressure that normally keeps the lung expanded, leading to breathing difficulties. These conditions highlight the pleura’s role in maintaining healthy respiratory mechanics.