The Pleurae and Pleural Cavities

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Azygos system of veins
| Main Anatomy Index | The lungs
Last updated 30 March 2006
The Pleurae and Pleural Cavities
- 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 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 1st 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.
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
4th costal cartilage.
- Here it passes to the left margin of the sternum and then continues inferiorly to the 6th 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 8th rib in
the midclavicular line, the 10th
rib in the midaxillary line, and the 12th rib at its neck or inferior to it.
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 4th
and 5th 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.
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
| Parietal pleura |
costal: intercostal nerves
mediastinal & diaphragmatic: phrenic nerve |
| Visceral pleura |
autonomic nerves from the pulmonary plexuses |
