Definition: the pleura is a membrane of fibrous tissue covered by a single layer of very flat cells. It covers each lung and lines the containing cavity.
Parts: the pleura is made of 2 parts: visceral part and the parietal part
A. Visceral part: it is moist and shining. It closely covers the lung and adheres to all its surfaces. It provides the lung with a smooth slippery surface that allows it to move freely on the parietal pleura.
B. Parietal pleura: this forms the external wall of the pleura cavity. It adheres to the thoracic wall and diaphragm by connective tissue. It has many parts:
– the costal pleura: this covers the inner surfaces of the sternum, costal cartilages, ribs, intercostal muscles and the sides of the thoracic vertebrae
– mediastinal pleura: this part covers the mediastinum
– the diaphragmatic pleura: this part covers the superior surface of the diaphragm lateral to the mediastinum.
– the cervical pleura: this is the dome-shaped apex of the pleural sac. It is the continuation of the costal and the mediastinal layers of pleura that covers the apex of the lungs.
Arterial supply: the arterial supply of the parietal pleura is from the intercostal, internal thoracic and musculophrenic arteries. The visceral pleura is supplied by the bronchial arteries
Venous drainage: veins from the parietal pleural joins the systemic veins. Veins from the visceral pleural drains into the pulmonary veins.
Lymph drainage: lymph from the parietal pleura drains into the intercostal, parasternal, posterior mediastinal and diaphragmatic nodes. Lymph from the visceral part drains into the nodes in the hila of the lungs.
Clinical correlates:
1. The potential space between the two layers of pleura may be filled with air (pneumothorax), blood (haemothorax) or pus (pyothorax)
2. Fluid can be drained from the pleural cavity by inserting a wide bore needle through an intercostal space.
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