Each lung is enclosed in a serous pleural sac consisting of two membranes: the parietal pleura and the visceral pleura. The parietal pleura is the thicker of the two membranes and it lines the pulmonary cavities. It adheres to the thoracic wall, the mediastinum and the diaphragm.
The parietal pleura consists of parts that are named according to the different parts of the body that they are in contact with. These include the:
- the costal part
- the mediastinal part
- the diaphragmatic part
- the cervical part
The costal part of the parietal pleura envelops the inner surfaces of the thoracic wall. It is separated from the inner surface of the thoracic wall - including the sternum, ribs, costal cartilages, intercostal muscles and membranes, as well as the sides of the thoracic vertebrae- by a layer called endothoracic fascia. This fascia is a thin layer of loose connective tissue that serves as a separation plane when there is need for surgical separation of the costal pleura from the thoracic wall.
The mediastinal part of the parietal pleura covers the the lateral parts of the mediastinum. It extends upwards into the neck as the cervical pleura and maintains continuity with the costal pleura anteriorly and posteriorly, as well as the diaphragmatic pleura inferiorly. Above the lung root, the mediastinal pleura forms a continuous sheet that continues anteroposteriorly between the sternum and the vertebral column. At the hilum of the lung, it folds laterally onto the root of the lung and continues into the visceral pleura.
The diaphragmatic part of the parietal pleura covers the superior or thoracic surface of the diaphragm on each side of the mediastinum. This, however, excludes the costal attachments at which the diaphragm fuses with the pericardium. The diaphragmatic pleura connects to the muscular fibers of the diaphragm through a thin and more elastic layer of endothoracic fascia known as the phrenicopleural fascia.
The costal part of the parietal pleura covers the apex of the lung. It forms a dome-like structure called the pleural cupula over the apex and reaches its highest point approximately 2-3 cm above the level of the medial third of the clavicle. The cervical pleura is supported by a fibrous extension of the endothoracic fascia known as the suprapleural membrane or Sibson fascia. This fascia attaches to the inner edge of the first rib and the transverse process of the seventh cervical vertebra.
As the parietal pleura abruptly reflects from one wall to another, it forms lines of pleural reflection. These lines mark the boundaries of the pulmonary cavities and include three distinct lines on each side: sternal, costal, and diaphragmatic lines of pleural reflection. These lines of pleural reflection delineate the extent of the pleural cavities.
The blood supply of the parietal pleura is similar to that of the thoracic wall in that it is derived from the intercostal arteries.
The parietal pleura receives innervation the phrenic nerve (C3-C5) and the intercostal nerves (T1-11). This is through from somatic afferent fibers that therefore enable the parietal pleura to have sensitivity to pressure, pain and temperature stimuli.
Latin: pleura parietalis
|Parts of the parietal pleura:
|Blood supply: intercostal arteries
Innervation: Intercostal nerves (T1-T11) and phrenic nerve (C3-C5)
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