Pulmonary pleurae

Pulmonary pleurae
Lung detail showing the pleurae. The pleural cavity is exaggerated since normally there is no space between the pulmonary pleurae.
Details
Pronunciation	/ˈplʊərə/
System	Respiratory system
Nerve	Intercostal nerves, phrenic nerves, vagus nerve
Identifiers
Latin	pleurae pulmonarius
MeSH	D010994
TA98	A07.1.02.001
TA2	3322
TH	H3.05.03.0.00001
FMA	9583
Anatomical terminology [edit on Wikidata]

The pulmonary pleurae (sg.: pleura)^[1] are the two flattened sacs ensheathing each lung, locally appearing as two opposing layers of serous membrane separating the lungs from the mediastinum and the inside surfaces of the surrounding chest walls.

The portion of the pleura that covers the surface of each lung is often called the visceral pleura. This can lead to some confusion, as the lung is not the only visceral organ covered by the pleura. The pleura typically dips between the lobes of the lung as fissures, and is formed by the invagination of lung buds into each thoracic sac during embryonic development.^[2] The portion of the pleura seen as the outer layer covers the chest wall and is often called the parietal pleura. It lines the inner surfaces of the thoracic cavity on each side of the mediastinum, and can be subdivided into mediastinal (covering the lateral surfaces of the fibrous pericardium, oesophagus and thoracic aorta), diaphragmatic (covering the upper surface of the diaphragm), costal (covering the inside of rib cage) and cervical (covering the underside of the suprapleural membrane) pleura. The visceral and the mediastinal parietal pleurae are connected at the root of the lung ("hilum") through a smooth fold known as pleural reflection, and a bell sleeve-like extension of visceral pleura hanging under to the hilum is known as the pulmonary ligament.

Between the two layers of the pleura is what historically has been referred to as a potential space, which in reality is an actual space of about 15 μm. This is called the pleural cavity (also pleural space).^[2] It contains a tiny amount of serous fluid (pleural fluid) secreted by the pleurae, at a pressure below the atmospheric pressure under healthy conditions. The two lungs, each bounded by a two-layered pleural sac, almost fill the thoracic cavity.