pleuraa

Pleurae are the pair of serous membranes that enclose the lungs and line the thoracic cavity. In humans, the pleural system consists of two layers: the visceral pleura, which tightly covers the lungs including their fissures, and the parietal pleura, which lines the inner aspect of the thoracic wall, the diaphragm, and the mediastinum. The visceral and parietal layers are continuous at the lung hilum, and the space between them is the pleural cavity, normally a potential space containing a small amount of lubricating pleural fluid.

The pleural fluid lubricates the pleural surfaces and, together with the negative intrapleural pressure, helps keep the lungs expanded during respiration. The parietal pleura is subdivided into regions corresponding to the chest wall and surrounding structures: the costal, diaphragmatic, mediastinal, and cervical (cupula) pleura. The visceral pleura is innervated primarily by autonomic nerves and is less sensitive to pain, whereas the parietal pleura is supplied by intercostal and phrenic nerves and is a common source of pleural pain when inflamed.

Developmentally, pleurae arise from mesoderm-derived serous membranes of the coelomic cavity. The pleural cavity may contain small amounts of fluid under normal conditions and can become pathologically distended in disease.

Clinical relevance includes pleuritis (pleurisy), pleural effusion (excess fluid in the cavity), pneumothorax (air in the cavity leading to lung collapse), and hemothorax (blood in the cavity). Thoracentesis is a procedure to drain pleural fluid for diagnostic or therapeutic purposes.