The Pleura

The pleura is a thin membrane of connective tissue, lie on the either side of the mediastinum within the chest cavity. Each pleura has two layers parietal pleura and the cervical pleura.

Parietal pleura

The parietal pleura, which lines the thoracic wall, covers the thoracic layer of the diaphragm, and the lateral aspect of the mediastinum, and extends into the root of the neck to line the undersurface of the supra-pleural membrane at the thoracic outlet. 

Cervical pleura

The cervical layer of the mediastinum covers outer surfaces of the lungs and extends deep into the depths of the interlobar fissures.

The two layers of the pleura become continuous with each other forming cuff of the pleura, near to the hilum of the lung. The cuff of pleura hangs down to allow movement of the blood vessels and bronchi during respiration, this structure is referred to as pulmonary ligament.

Between these two layers, a small space is situated called pleural cavity. To avoid confusion with thorax cavity it is referred to as pleural space. Pleural space contains a fluid, usually 5 to 10ml in normal conditions. It acts as the lubricant between two layers. 

Nerve supply of the pleura

The pleura is innervated by both sensory nerves and autonomic nerves, depending on the surface which it covers.

The parietal pleura is sensitive to pain, temperature, touch and pressure and is supplied as follow:

The mediastinal pleura is supplied by the phrenic nerves.

The costal pleura is segmentally supplied with intercostal nerves.

The mediastinal pleura is supplied over the domes by the phrenic nerves and around the periphery by lower six intercostal nerves.

The cervical pleura is insensitive to the pain, touch, and pressure but is sensitive to the stretch. It receives autonomic nerve supply from the pulmonary plexus.

Pleural effusion

It is a condition during which the fluid in the pleural cavity increases abnormally due to any inflammation and malignancy or impairs the drainage of the fluid, resulting in decreased lung expansion, sound and dullness on percussion over the effusion. 

The presence of 300ml of fluid in the costodiaphragmatic recess in an adult is sufficient to enable its clinical detection.

Pleurisy

Inflammation of the pleura secondary to the inflammation of the lung results in the pleural surface becoming coated with inflammatory exudate, causing the surfaces to be roughened. This roughening produce friction, resulting in severe pain, this medical condition is referred to as pleurisy.