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Pleural cavity
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In human anatomy, the pleural cavity is the body cavity that surrounds the lungs. The lungs are surrounded by the pleurae, a serous membrane which folds back upon itself to form a two-layered, membrane structure. The thin space between the two pleural layers is known as the pleural space; it normally contains a small amount of pleural fluid. The outer pleura (parietal pleura) is attached to the chest wall. The inner pleura (visceral pleura) covers the lungs and adjoining structures, i.e.
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Encyclopedia
In human anatomy, the pleural cavity is the body cavity that surrounds the lungs. The lungs are surrounded by the pleurae, a serous membrane which folds back upon itself to form a two-layered, membrane structure. The thin space between the two pleural layers is known as the pleural space; it normally contains a small amount of pleural fluid. The outer pleura (parietal pleura) is attached to the chest wall. The inner pleura (visceral pleura) covers the lungs and adjoining structures, i.e. blood vessels, bronchi and nerves.
The parietal pleura is highly sensitive to pain; the visceral pleura is not, due to its lack of sensory innervation.
Functions
The pleural cavity, with its associated pleurae, aids optimal functioning of the lungs during respiration. The pleurae are coated with lubricating pleural fluid which allows the pleurae to slide effortlessly against each other during ventilation. Surface tension of the pleural fluid also leads to close apposition of the lung surfaces with the chest wall. This physical relationship allows for optimal inflation of the alveoli during respiration. Movements of the chest wall, particularly during heavy breathing, are coupled to movements of the lungs since the closely opposed chest wall transmits pressures to the visceral pleural surface and, hence, to the lung itself.
Development of the pleural cavity
Comparative Anatomy
In humans, there is no anatomical connection between the left and right pleural cavities, so in cases of pneumothorax, the other lung will still function normally unless there is a tension pneumothorax which may collapse the contralateral parenchyma, blood vessels and bronchi.
Blood supply
In humans, the visceral pleura receives its blood supply from the bronchial circulation.
Pleural fluid
Pleural fluid is a serous fluid produced by the pleurae. In normal pleurae, most fluid is produced by the parietal circulation (intercostal arteries) via bulk flow and reabsorbed by the lymphatic system. Thus, pleural fluid is produced and reabsorbed continuously. In a normal 70 kg human, a few milliliters of pleural fluid is always present within the intrapleural space. Larger quantities of fluid can accumulate in the pleural space only when the rate of production exceeds the rate of reabsorption. Normally, the rate of reabsortion increases as a physiological response to accumulating fluid, with the reabsorption rate increasing up to 40x before significant amounts of fluid accumulate within the pleural space. Thus, a profound increase in the production of plural fluid, or some blocking of the reabsorbing lymphatic system, is required for fluid to accumulate in the pleural space.
When accumulation of pleural fluid is noted, cytopathologic evaluation of the fluid, as well as clinical microscopy, microbiology, chemical studies, tumor markers, pH determination and other more esoteric tests are required as diagnostic tools for determining the causes of this abnormal accumulation. Even the gross appearance, color, clarity and odor can be useful tools in diagnosis. The presence of heart failure, infection or malignancy within the pleural cavity are the most common causes that can be identified using this approach.
In spite of all the diagnostic test available today, many pleural effusions remain idiopathic in origin. This can be quite vexing to the patient, family and phisicians involved. If severe symptoms persist, more invasive techniques my be required. In spite of the lack of knowledge of the cause of the effusion, treatment my be required to relieve the most common symptom, which is dyspnea, as this can be quite disabling. Thoracoscopy has become the mainstay of invasive procedures as closed pleural biopsy has fallen into disuse.
See also
*Pleural disease
Additional images
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