Pleura
The pleurae (sing.: pleura) are two flattened sacs filled with fluid that surround each lung. Each pleura - left and right - is a serous membrane that separates the corresponding lung from the chest wall, the diaphragm and the mediastinum. Although wrapped onto the lung resulting in a double layer, each pleural membrane is a single, continuous structure.
The part of each pleura that covers the surface of the lung is the visceral pleura. The pleura typically dips between the lobes of the lung as fissures, and is formed by the invagination of lung buds into each thoracic sac during embryonic development. The part of the pleura that lines the chest wall, covers the diaphragm and other structures in the mediastinum such as major blood vessels, trachea, esophagus and the fibrous pericardium is the parietal pleura.
The parietal pleura can be subdivided in regions. The cervical pleura goes into the root of the neck; the costal pleura lies next to the ribs; the mediastinal pleura covers the mediastinum, and the diaphragmatic pleura covers the upper surface of the diaphragm.
At the root of the lung the visceral and parietal pleurae meet and form the hilum. A bell sleeve-like extension of the pulmonary pleura hanging under the hilum is known as the pulmonary ligament.
Between the two layers of the pleura is a space of about 15 μm, called the pleural cavity (also pleural space). It contains about 10 ml of serous fluid (pleural fluid) secreted by the pleurae, at an average pressure that is below the atmospheric pressure under healthy conditions. The two lungs, each bounded by a two-layered pleural sac, almost fill the thoracic cavity.
Similar Artists