Pleura of the Lungs

The pleura consists of two layers: the visceral pleura, which lines the external lung surface, and the parietal pleura, the outer layer that contacts the thoracic wall, mediastinum, and diaphragm. These layers are separated by the mediastinum, with each lung enveloped by its respective pleura.

Pleural fluid, secreted by mesothelial cells, lubricates the pleural surfaces to reduce friction during respiration. It creates surface tension that adheres the lungs to the thoracic wall and enables the cohesive property that allows lung expansion with the thoracic wall during breathing, helping the lungs fill with air.

The pleurae compartmentalize the thoracic cavity, isolating major organs to prevent disruption from heart and lung movement. They also limit the spread of infections between organs and create a boundary that protects the moving heart and lungs from interfering with each other's function.

Pleurisy is inflammation of the pleural membranes, often caused by pneumonia. The inflammation roughens the pleural surfaces, causing friction between the visceral and parietal layers during breathing, which results in stabbing pain and discomfort. This condition significantly impacts respiratory comfort.

Air accumulation causes pneumothorax, blood causes hemothorax, and pus causes pyothorax. Pneumothorax often results from chest surgery or penetrating trauma and may lead to total lung collapse. Treatment involves removing the accumulated substance from the pleural space, often using a chest tube to facilitate lung re-expansion.

The right and left lungs are enveloped by their respective pleurae and separated by the mediastinum, a central compartment containing the heart and other structures. The parietal pleura of each side contacts the mediastinum, creating distinct pleural cavities that isolate each lung.

Surface tension created by pleural fluid helps keep the lungs adhered to the thoracic wall, ensuring coordinated expansion during inhalation. This adhesion is critical to pressure relationships in thoracic cavity dynamics, allowing the lungs to expand as the chest cavity enlarges and maintaining the mechanical efficiency of breathing.