The pleura (also known as the pleural membrane) is a serous membrane made up of two layers: the outer pleura (called the parietal pleura), and the inner pleura (called the visceral pleura). Both layers are covered by mesothelial cells, which are specialized pavement-like cells found in vital organs.
The parietal pleura is in contact with the inside of the ribcage, the mediastinum, and the superior edge of the diaphragm. The mediastinum is a division of the thoracic cavity where the heart and other vital structures are located. The visceral pleura covers the surface of the lungs.
Located between the parietal and visceral pleura is the pleural cavity. This space is filled with a small amount of pleural fluid, which functions to keep each pleura humid and prevents friction when the lungs move during breathing.
Pleural fluid lubricates the pleural membranes. The fluid is produced by blood vessels of the pleural membranes at a rate of approximately 0.6 mL/hour and is absorbed by the parietal pleural lymphatic system at a similar rate. The lymphatic system is a network of blood vessels through which a fluid containing white blood cells (known as lymph) drains from a tissue to the blood. Disturbances in the balance of pleural fluid production and absorption rates can cause harmful accumulation of pleural fluid.
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Try it nowLet's look at the layers of the pleural membrane.
The parietal pleura is 30 to 40 micrometers thick and is in contact with the inside of the ribcage, the mediastinum and the upper surface of the diaphragm. The parietal pleura receives its blood supply from the intercostal arteries (arteries between the ribs). It is sensitive to pain and is highly involved in the formation of parietal fluid.
One of the remarkable features of parietal pleura is the presence of lymphatic stomata over its surface. Stomata are holes that open into the pleural space and function as the primary site of removal of pleural fluid from the pleural space.
The visceral pleura covers the surface of the lungs. It receives its blood supply from the bronchial (lung) circulation. The thickness of the visceral pleura varies over the surface of the lung, ranging from 20 to 80 micrometers. Due to its lack of sensory innervation, the visceral pleura is not sensitive to pain. The visceral pleural connective tissue dissipates stresses in the lung, and minimizes overexpansion of the lung thereby reducing the risk of pneumothorax.
A pneumothorax is a collapsed lung, and occurs when air enters the space between the chest wall and the lung (the pleural cavity). As air accumulates in this space, it pushes on the lung and causes it to collapse. Treatment involves inserting a needle or chest tube into the pleural cavity to remove the excess air. A pneumothorax can occur after a penetrating chest injury. Patients with pneumothorax feel chest pain and shortness of breath.
Pneumothoraxes are classified according to their cause. A primary spontaneous pneumothorax occurs without an apparent cause and in the absence of significant lung disease. A secondary spontaneous pneumothorax occurs in the presence of existing lung disease (e.g. tuberculosis). A traumatic pneumothorax develops from physical trauma.
The main function of the pleura is to provide mechanical protection and a smooth, lubricating elastic surface for the lungs to move during breathing.
The pleural membrane also has secondary functions, such as maintaining homeostasis in the pleural space through immunologic and metabolic responses. For example, during infections in the pleural space, the pleural membrane recruits inflammatory phagocytic cells and allows ready passage of necessary proteins from the blood vessels into the pleural space. Phagocytes are immune cells that provide protection by finding and destroying foreign particles like bacteria or dying cells.
The pleural cavity is a closed space between the visceral and parietal pleura that exists at sub-atmospheric pressure. Pleural cavity pressure is usually lower than the pressure in the lungs. The pressure difference between the pleural space and the alveolar space in the lung is defined as transpulmonary pressure, and is normally positive in value. The positive pressure difference allows the lungs to remain inflated under normal conditions. In humans, there is no anatomical connection between the pleural cavities.
The only mammal without a pleural cavity is the elephant! Instead of a pleural cavity, there is connective tissue. Despite many hypotheses, there is not a convincing explanation for this anatomic peculiarity.
The pleural cavity is located between the visceral pleura and the parietal pleura. It is 10 to 20 micrometers wide and extends completely around the lung.
The pleural cavity supports the optimal functioning of the lungs when breathing. It contains the pleural fluid, which serves as a lubricated space for the lungs to move freely during normal breathing, and transmits movements of the chest wall to the lungs to facilitate heavy breathing.
The pleura is a serous membrane made up of the outer parietal pleura, and the inner visceral pleura. Both layers are covered by mesothelial cells. The surface of each pleura interface is approximately 1000 {eq}cm^2 {/eq}.
The parietal pleura is in contact with the inside of the ribcage, the mediastinum, and the superior surface of the diaphragm. The visceral pleura covers the surface of the lungs. Between the parietal and visceral pleura is the pleural cavity. This space is filled with a small amount of pleural fluid. Pleural fluid lubricates the pleural membrane by keeping the visceral and parietal pleura humid; It also reduces friction between the membrane layers when breathing.
The parietal pleura is sensitive to pain and is highly involved in the formation of parietal fluid. The visceral pleura lacks sensory innervation and therefore is not sensitive to pain. Only the parietal pleura has lymphatic stomata that opens into the pleural space. The visceral pleural connective tissue dissipates stresses in the lung and reduces the risk of a pneumothorax.
The pleura is crucial for the proper functioning of the lung. It provides mechanical protection and allows for a smooth, lubricating elastic surface for the lung movement when breathing.
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The pleural membrane provides protection and a smooth, lubricating elastic surface for lung movement when breathing. It also maintains the normal dynamic homeostasis in the pleural space.
The organs covered by the pleural membrane are the lungs. The pleural cavity is the space between the visceral and parietal pleura.
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