Pleura

At a glance

English

Pleura

Latin (TA2)

Pleura

System

Respiratory

Region

Thorax

Side

Single, on the midline

About the pleura

Each lung lies in its own closed pleural sac. The membrane has two continuous layers. The visceral pleura is stuck firmly to the surface of the lung and follows it into the fissures between the lobes. The parietal pleura covers the inner face of the thoracic wall, the domed top of the diaphragm and the side of the mediastinum. The two layers meet round the root of the lung at the hilum, and below the root this sleeve hangs down as a double fold called the pulmonary ligament.

The parietal layer is named by region. Costal pleura lines the ribs and intercostal spaces, separated from them by endothoracic fascia. Diaphragmatic pleura covers the dome of the diaphragm. Mediastinal pleura covers the pericardium, aorta, oesophagus and great veins. Cervical pleura, the cupula, rises above the first rib into the root of the neck under a fascial cover, the suprapleural membrane, which makes it vulnerable to needles placed for subclavian lines. Where one part turns into another the lung does not completely fill the space, leaving recesses; the costodiaphragmatic recess at the lower margin is where fluid first collects and where its sharp angle is checked on X-ray.

Between the layers lies the pleural cavity, normally only a film of a few millilitres of fluid. Each layer is a single sheet of mesothelial cells on loose connective tissue. The fluid lets the lung glide over the chest wall, while surface tension and a slightly negative pressure keep the two layers together, so the lung expands when the chest wall and diaphragm move outwards in breathing in.

Supply follows the underlying tissue. The visceral pleura shares the lung's vessels and has only autonomic nerves, so it cannot feel pain. The parietal pleura has somatic nerves, and inflammation of it, pleurisy, produces sharp pain worse on breathing, sometimes felt at the shoulder when the central diaphragm is involved. Fluid in the space, a pleural effusion, or air, a pneumothorax, lets the lung collapse and is drained with a needle or tube; repeated effusions may be treated by sealing the layers together.

Function and supply

Function

Lets the lungs slide smoothly against the chest wall and couples them to it, so that they follow the movements of breathing.

Nerve supply

Visceral pleura: autonomic fibres of the pulmonary plexus, insensitive to pain. Parietal pleura: intercostal nerves for the costal part and periphery of the diaphragm; phrenic nerves for the mediastinal and central diaphragmatic parts.

Blood supply

Visceral pleura: bronchial and pulmonary vessels of the lung surface. Parietal pleura: intercostal, internal thoracic, musculophrenic, pericardiacophrenic and superior phrenic arteries.