The pleura is the serous membrane that covers the lungs. It consists of two layers, referred to as the pleural layers: first, the parietal pleural leaflet (or parietal pleura), is located outside the lungs and separates them from the chest wall; the other, the visceral pleural, which adheres to the inner surface of the lung.

What is the pleura?

The pleura is the serous membrane that covers the lungs. The two pleural layers that form it are in continuous contact with each other: to ensure and facilitate the sliding of the lungs, the pleural layers have a thin film of pleural fluid which is located in the space between the two layers, the presence of which is essential to allow the lungs to follow the movements of the muscles to which they subscribe during breathing. The two sheets delimit the virtual cavity, the pleural cavity, which does not communicate with the exterior or with other organs. Within the pleural cavity, a negative pressure is formed that allows the lungs to expand during inhalation.

The neurovascular supply differs for both layers of the pleura. The innervation of the parietal pleura is provided through the intercostal nerves (innervate the costal and cervical pleura), which causes it to be sensitive to pain, pressure and temperature. The parietal pleura receives blood supply from the intercostal arteries.

On the other hand, the visceral pleura has an autonomic innervation from the pulmonary plexus (network of nerves that extend from the sympathetic trunk and the vagus nerve), which causes it not to be sensitive to pain or temperature. The visceral pleura receives blood supply from the internal thoracic arteries (bronchial circulation), which also supplies the parenchyma of the lungs.

The top of the pleura is called pleural parietal dome: it is placed exactly in the supraclavicular fossa and corresponds to the apex of the lung. From the histological point of view the pleura is regarded as a mesothelium, namely a fabric, which retains features typical both of the endothelium (the thin tissue that internally delimits the lumen in the blood or lymph vessels) and of the epithelia (the tissues that cover the outer surface or line the internal cavities of the body) and therefore, it histologically resembles either or both.

There are several serious disorders that can affect the pleura. These include pleurisy (inflammation of the pleura), pleural effusion (accumulation of excess fluid between the parietal and visceral pleurae), hemothorax (accumulation of blood in the pleural space), empyema (accumulation of pus in the pleural space), chylothorax (rupture of the thoratic duct), fibrothorax (encasement of the lung in fibrin after a severe pleural inflammatory process), and mesothelioma and other tumours that can affect the pleura.

What function does the pleura serve?

The pleural fluid between the pleural layers is essential in preventing the separation of the two layers and lubricates the surface so that the lungs can easily move within the thoracic cavity. The pleural fluid also provides surface tension to keep the lungs close to the thoracic wall. Thus, the pleurae allow the volume of the lungs to change along with the volume of the thoracic cavity and facilitate ventilation.