The word "Pleura" is a Greek word which when literally translated, means "side of the body". There are two pleural cavities, located in the thorax and they enclose the lungs. Due to the asymmetrical position of the heart in the mediastinum, the left pleural cavity is slightly smaller than the right pleural cavity. Both cavities, however, are lined by two serous layers, namely the visceral pleura which is also known as the pulmonary pleura and the parietal pleura.
The visceral pleura, lines the surface of the lung tissue, while the parietal pleura lines the thoracic cavity. The parietal pleura is attached to the endothoracic fascia of the chest wall and it is separated from the visceral pleura by a thin layer of serous fluid. The presence of this serous fluid between the two layers of pleura allows for the free sliding motion of the lungs within these cavities, while also allowing the two layers to remain held together through capillary action. The parietal pleura extends down to the level of the twelfth thoracic vertebral body T12 and also extends to the lateral margins of the diaphragm where it is known as the diaphragmatic part of the parietal pleura.
Due to the fact that the total capacity of the pleural cavity is greater than that of the lungs, recesses are present. The dome shape of the diaphragm results in the existence of the costodiaphragmatic recess, which is located over the side of the diaphragm that faces the ribs on either side. Another recess, known as the costomediastinal recess, is located anterior to the pericardium on both the left and right sides of the anterior mediastinum.
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