The lungs are surrounded by two membranes, the pleurae. The outer pleura is attached to the chest wall and is known as the Parietal pleura; the inner one is attached to the lung and other visceral tissues and is known as the Visceral pleura. In between the two is a thin space known as the pleural cavity or pleural space. It is filled with pleural fluid, a serous fluid produced by the pleura.

The pleural fluid lubricates the pleural surfaces and allows the layers of pleura to slide against each other easily during respiration. It also provides the surface tension that keeps the lung surface in contact with the chest wall. During quiet breathing, the cavity normally experiences a negative pressure (compared to the atmosphere) which helps adhere the lungs to the chest wall, so that movements of the chest wall during breathing are coupled closely to movements of the lungs.

The parietal pleura is highly sensitive to pain; the visceral pleura is not. The visceral pleura has a dual blood supply, from the bronchial and pulmonary arteries. In humans, there is no anatomical connection between the left and right pleural cavities, so in cases of pneumothorax (see below), the other hemithorax will still be able to function normally.

Diseases involving the pleura include:

·         Pneumothorax (collapsed lung): air enters the pleural cavity, either from the outside or from the lungs. This can be the result of a penetrating chest wound, or of an internal injury. A tension pneumothorax is where the punctured chest wall forms a one way valve so that air may enter (through the puncture) on inspiration, but cannot exit on expiration. With each breath air builds up in the chest cavity, compressing the lung still further, thus reducing the surface area available for gas exchange. It is a medical emergency.

·         Pleural effusion: fluid accumulates in the pleural space, compressing the lungs. This can result for example from lung cancer, infection or heart failure.

·         Mesothelioma: this is a type of cancer caused by asbestos exposure.

·         Pleurisy: an inflammation of the pleura, especially one causing painful respiration. Pleurisy can be provoked by a variety of infectious and non-infectious causes. The modern term for this is pleuritis, but the older term is still in common use.

From Wikipedia, the free encyclopedia

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