The pleural cavity (lat. Cavitas pleuralis or Cavum pleurae ) or the pleural space is the narrow (capillary) gap (space) in the chest cavity between the wall sheet and the lung covering of the pleura ( pleura ). Since this space is very small, the term pleural space is also used.
A pleural cavity is only found in mammals , except in proboscis . With them, the space between the wall sheet and the lung covering of the pleura is fused by connective tissue . Instead of a pleural cavity, birds have an air sac system .
Physiologically, there is a relative negative pressure in the pleural cavity . The pleural space is filled with a serous fluid (about 5–10 ml in adults) through which the parietal and visceral sheets of the pleura “stick” together. The restoring force of the lungs and the tendency of the thorax to expand counteract each other. The resulting negative pressure in the gap and the adhesive force of the liquid prevent the lungs from collapsing.
The pressure difference from the outside air is at inhalation about -800 Pa in exhalation -500 Pa. The lower pressure during inhalation is explained by the resilience of the organ, which increases when the lungs are “inflated”, due to its elasticity. With strongly forced exhalation (with the support of the auxiliary respiratory muscles such as the chest muscles ), the so-called intrapleural pressure during exhalation can also assume positive values. These can even reach up to +15 kPa (110 mmHg) with a glottic closure (see also Valsalva maneuver ).
- A pathological accumulation of fluids in the pleural cavity is called a hemothorax ( blood ) or chylothorax ( lymph ), respectively .
- A puncture of the pleural cavities is called a pleural puncture (also thoracentesis ).
- When a needle is inserted or the chest wall is injured, the pressure is inevitably equalized and thus a pneumothorax occurs .
- During the Spanish flu , which spread between 1918 and 1920 , autopsies showed that foci of inflammation were found within the lungs , mostly in the lower lobes, and that in many the pleural cavity was suppurated (see pleural empyema ).
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