The Pleurae and Pleural Cavities

Azygos system of veins | Main Anatomy Index | The lungs

Last updated 30 March 2006

The Pleurae and Pleural Cavities

• A pleural sac surrounds each lung.
• A parietal layer of pleura forms its external wall and a visceral layer the internal wall that invests the lungs.

• The pleura cavity is a separate and closed potential space.
• Normally it contains only a capillary layer of serous fluid with lubricates the two layers of pleura and reduces friction.

The Visceral Pleura

• The moist and shiny visceral (pulmonary) pleura closely covers the lung and is adherent to all its surfaces.
• It provides the lung with a smooth, slippery surface for free movement in the parietal pleura.
• The visceral pleura dips into the fissures of the lungs so that the lobes are covered by it.

• The visceral pleura is continuous with the parietal pleura at the root of the lung, where structures enter and leave it.

The Parietal Pleura

• This is the external wall of the pleura cavity and is adherent to the thoracic wall and diaphragm by connective tissue.
• The parietal pleura is also attached to the pericardium.

• The parietal pleura is given different names according to the parts with which it is associated: costal pleura (ribs and sternum); mediastinal pleura (mediastinum); diaphragmatic pleura (diaphragm); and pleural cupula (apex of the lung).

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The Costal Pleura

• This part of the parietal pleura covers the internal surfaces of the sternum, costal cartilages, ribs, intercostal muscles, and the sides of the thoracic vertebrae.
• It is separated from these structures by a thin layer of connective tissue, called endothoracic fascia.

The Mediastinal Pleura

• This part of the parietal pleura covers the mediastinum.
• It is continuous with the costal pleura anteriorly and posteriorly; with the diaphragmatic pleura inferiorly; and with the cupula or cervical superiorly.

• Superior to the root of the lung, the mediastinal pleura is a continuous sheet between the sternum and vertebral column.

• At the root of the lung, the mediastinal pleura passes laterally, where it encloses the structures in the root, and becomes continuous with the visceral pleura.

• Inferior to the root of the lung, the mediastinal pleura passes laterally as a double layer from the oesophagus to the lung, where it is continuous with the visceral pleura.
• This double layer of pleura is called the pulmonary ligament.
• It is continuous superiorly with the mediastinal pleura and ends inferiorly in a free border.

The Diaphragmatic Pleura

• This part of the parietal pleura covers the superior surface of the diaphragm, lateral to the mediastinum.

The Pleural Cupula or Cervical Pleura

• The pleural cupula is the dome-shaped apex of the pleural sac that is formed by the cervical pleura.
• The pleural cupula is the continuation of the costal and mediastinal layers of pleura that covers the apex of the lung.

• It extends superiorly posterior to the clavicle and 1^st rib and passes through the superior thoracic aperture into the root of the neck.
• Its summit is nearly 3 cm superior to the level of the medial third of the clavicle.

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Pleural Reflections

• These are the relatively abrupt lines along which the parietal pleura folds back or changes direction from one wall of the pleura cavity or another.
• They occur where the costal pleura becomes continuous with the mediastinal pleura anteriorly and posteriorly, and with the diaphragmatic pleura inferiorly.

Sternal Line of Reflection (Anterior Costomediastinal Reflection)

• This is where the costal pleura is continuous with the mediastinal pleura, posterior to the sternum.

• The right and left sternal reflections are indicated by lines that pass inferomedially from the sternoclavicular joints to the anterior median line at the level of the sternal angle.

• On the right side, the sternal line of reflection passes inferiorly in the medial plane to the posterior aspect of the xiphoid process, where it turns laterally.

• On the left side, the sternal line of pleura reflection passes inferiorly in the median plane to the level of the 4^th costal cartilage.
• Here it passes to the left margin of the sternum and then continues inferiorly to the 6^th costal cartilage.

The Costal Line of Pleural Reflection

• This is where the costal pleura is continuous with the diaphragmatic pleura.
• It passes obliquely across the 8^th rib in the midclavicular line, the 10^th rib in the midaxillary line, and the 12^th rib at its neck or inferior to it.

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The Pleural Recesses

• During deep inspiration, the lungs fill the pleural cavities, but during quiet respiration, the lungs do not occupy parts of these cavities.
• Here, portions of the parietal pleura and in contact.
• These potential spaces are called pleura recesses.

The Costodiaphragmatic Recesses

• These are slit-like intervals between the costal and diaphragmatic pleurae on each side.
• They become alternatively smaller and larger as the lungs move in and out of them during inspiration and expiration.

The Costomediastinal Recesses

• These potential spaces lie along the anterior margin of the pleura.
• Here, the costal and mediastinal parts of the parietal pleura come into contact.

• The left recess is larger because of the presence of a semicircular deficiency, the cardiac notch, in the left lung anterior to the pericardium.

• The costomediastinal recesses lie at the anterior ends of the 4^th and 5^th intercostal spaces.
• During inspiration and expiration, a thin tongue-like edge of the left lung, called the lingula (L. dim. of lingua, tongue), slides in and out of the left costomediastinal recess.

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Arterial Supply of the Pleurae

• The arterial supply of the parietal pleura is from the arteries that supply the thoracic wall (intercostal, internal thoracic, and musculophrenic arteries).

• The arterial supply of the visceral pleura is from the bronchial arteries, which are branches of the thoracic aorta.

Innervation of the Pleurae

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