Serous membranes encapsulate the lungs and the thoracic cavity. This lining is known as pleura. The visceral pleura is adjoined to the outside of the lung, but also protrudes into each of the lobular fissures. The thoracic walls and the diaphragm are lined with parietal pleura. The boundary of the mediastinum is created by the continuation of the parietal pleura, as well as the space between the lungs.


The pleural cavity, which is little more than a slit, is positioned between the visceral and parietal pleura. The pleura houses liquid, which enables the internal organs to easily move past each other during the course of breathing. The pleural ligament refers to the reflection of the layers of pleura which extend inferiorly. These are found at the root of each lung. The primary responsibility of the pleural ligaments is to provide support for the lungs.

The lungs are basically held fast to the thoracic wall thanks to the way the moist membranes of both the visceral and parietal pleura stick together. The interpleural space, also known as the pleural cavity, which is positioned between these two membranes is nothing more than slight layer of fluid which is produced by the membranes. This creates suction, similar to two wet pieces of glass lying flush against each other. The pleural cavity does not really exist in a healthy body. In order for the cavity to develop, the body either must die or there must be a significant disease attacking the area.


Image: Pleurae

The lungs and the thoracic cavity enlarge and shrink in unison during breathing because the lungs are held to the thoracic wall via suction. The pleural cavity, the pericardial cavity, the mediastinum, and the thoracic cavity create the four compartments of the thorax. The lungs are housed within the pleural cavity while the heart is housed within the pericardial cavity.


The mediastinum is responsible for providing protection for the esophagus, thoracic duct, segments of the respiratory tract, major vessels, and some nerves. This compartmentalization helps to protect the visceral organs within the various cavities from harm. Infections are typically not able to travel from on compartment to another, wounds can shut down one section and leave the other three in full function, and organ damage is typically restricted to just one organ. Pleurisy, a serious infection of the pleura, will typically only affect one side of the cavity while a knife wound can shut down only one the affected segment.
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