The pleura (plural: pleurae) is an exceedingly delicate two-layered serous membrane arranged as a closed, invaginated sac that encloses the lungs and lines the thoracic cavity.
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Terminology
There are many terms related to the pleura 4:
pleural: disease or condition that arises from or involves the pleura
pleura-based: disease or condition that touches the pleura but does not arise from it
subpleural: diseases or conditions that are near to but do not touch the pleura (NB the descriptor "peripheral" is now preferred 4)
extrapleural: external (superficial) to the pleura but not touching the pleura itself
Gross anatomy
The pleura divides into:
visceral pleura: covers the surface of the lung and dips into the fissures between its lobes
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parietal pleura: lines the inner of the chest wall and named according to the site it lines
cervical pleura
costal pleura
diaphragmatic pleura
mediastinal pleura
The visceral pleura is attached directly to the lungs, while the parietal pleura is attached to the opposing thoracic cavity. The space between these two delicate membranes is the pleural space, which contains a small volume of lubricating pleural fluid 4.
The pleural fissures are formed by the visceral pleura separating two adjacent lobes:
accessory fissures: formed within the same lobe
Contraction of the diaphragm causes a relative negative pressure within this space and forces the lungs to expand, resulting in passive inhalation. This process can be made forceful through the contraction of the external intercostal muscles, forcing the rib cage to expand and adding to the relative negative pressure within the pleural space, which causes the lungs to fill with air.
Lines of pleural reflection
The lines of pleural reflection outline where parietal pleura abruptly changes direction as it passes from one wall of the pleural cavity to another. Right and left parietal pleura reflect in an asymmetric manner due to the presence of the heart:
Above the clavicle: the pleura begin approximately 1" above the mid-point of the medial third of the clavicle
2nd rib: both right and left pleural lines descend down the midline
4th rib: left pleural line deviates laterally to accommodate the heart
6th rib: both right and left pleural lines deviate laterally to accommodate the heart
8th rib: both right and left pleural lines pass midclavicular line (MCL)
10th rib: both right and left pleural lines pass midaxillary line (MAL)
12th rib: both right and left pleural lines travel posteriorly around the chest wall
The visceral pleura remains roughly two ribs higher than the lines of pleural reflection in the lower thorax (e.g. visceral pleura crosses MAL at the level of the 8th rib). The surface markings of the lines of pleural reflection are important to know as an incision or puncture along these lines can inadvertently cause a pneumothorax or a hemothorax.
Pleural recesses
The lungs do not completely fill the anterior and posterior regions of pleural cavities resulting in the formation of pleural recesses. These recesses provide potential spaces in which fluid can collect, they include:
costodiaphragmatic recesses (also called costophrenic recesses)
costomediastinal recesses
phrenicomediastinal recesses
vertebromediastinal recesses
Arterial supply
parietal pleura is supplied by the internal thoracic artery, anterior and posterior intercostal arteries, subclavian artery and phrenic arteries
visceral pleura is supplied by the bronchial arteries
Venous drainage
parietal pleura is drained by the internal thoracic, intercostal and phrenic veins
visceral pleura is drained by the pulmonary veins
Lymphatic drainage
lymphatic vessels drain to lymph nodes within the deep pulmonary plexus
Innervation
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parietal pleural
costal pleura: intercostal nerves
mediastinal: phrenic nerves
diaphragmatic pleura: peripherally innervated by the intercostal nerves and centrally innervated by the phrenic nerves
visceral pleura: nerves from the pulmonary plexus
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