Pleura
Last reviewed: 23.04.2024
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Pleura (pleura) is a thin serous membrane enveloping each lung (visceral pleura) and lining the walls of its pleural cavity (parietal pleura). It is formed by a thin connective tissue base covered with a flat epithelium (mesothelium) located on the basal membrane. Mesothelium cells are flat in shape, have a lot of microvilli on the apical surface, slightly developed organelles. The connective tissue base is formed by layers of collagen and elastic fibers alternating like lattices; contains separate bundles of smooth myocytes and a small number of cells of connective tissue.
It covers the parenchyma of the lungs, the mediastinum, the diaphragm and lining the inner surface of the chest. The parietal and visceral pleurae are covered with a single layer of flat mesothelial cells.
Visceral (pulmonary) (pleura visceralis, s.pulmonalis) covers the lungs from all sides, firmly fuses with its surface, enters the gap between the lobes. On the anterior and posterior surfaces of the lung root, the visceral passes into the parietal (mediastinal) pleura. From the root of the lung, the anterior and posterior leaves of the visceral pleura form a vertically oriented fold - the ligamentous ligament (lig.pulmonale) that descends up to the diaphragm. This ligament is located in the frontal plane between the medial surface of the lung and the parietal pleura leaf adjacent to the mediastinum.
The parietalis (pleura parietalis) is a continuous leaflet that forms a receptacle for the lung in each half of the thoracic cavity, fusing with the inner surface of the thoracic cavity and the mediastinal surface. In the parietal, the rib, mediastinal and diaphragm parts are distinguished.
In parietal mesothelial cells are located directly on the layer of connective tissue. In the visceral layer of mesothelial cells is located on a thin connective layer, which is associated with a deeper layer of connective tissue (the main connective tissue layer). Between the main layer of the visceral pleura and the borderline subpleural layer of the lung, the vascular layer is located. In the vascular layer there are lymphatic vessels, veins, arteries, capillaries, the diameter of the capillaries considerably larger than the diameter of the capillaries in other tissues of the body, which helps maintain low capillary pressure in the visceral pleura. There are differences in the ratio of blood and lymph vessels in the visceral and parietal pleura. In parietal 2-3 times more lymph vessels than blood vessels, in visceral - the ratio of the reverse - the blood vessels more than the lymphatic. The most active is the intercostal (costal) pleura, in it there are lymphatic "hatches" of round or oblong form, through which the lymph vessels of the parietal (costal) pleura are connected with the pleural cavity.
The pleura costalis covers the inner surface of the ribs and intercostal spaces from the inside. In front of the sternum and behind - in the spine the rib goes into the mediastinal pleura.
The mediastinal (pleural mediastinalis) limits the mediastinal organs on the lateral side, separating them from the pleural cavity of the corresponding lung (right or left). The mediastinal pleura proceeds from the inner surface of the sternum in front to the lateral surface of the vertebral column from behind. Mediastinal is fused with the pericardium, in the region of the lung root it passes into the visceral pleura.
At the top of the head 1 of the rib, the rib and mediastinal pleura intersect into each other, forming a dome of the pleura (cupula pleurae). The subclavian artery and the vein adjoin the dome of the pleura from the front and medially. Below the rib and mediastinal pleura pass into the diaphragmatic pleura. The diaphragmatic (pleura diaphragmatica) covers the diaphragm from above, except for its central portions, to which the pericardium is attached.
The pleural cavity (cavitas pleuralis) is located between the parietal and visceral in the form of a narrow neck, it contains a small amount of serous fluid moistening the pleura leaf, which helps to reduce the friction of the visceral and parietal pleura sheets against each other during respiratory movements of the lungs. In the areas of the transition of the costal pleura to the mediastinal and into the diaphragmatic pleura, there are cavities in the pleural cavity - pleural pockets (sinuses). They are the reserve spaces of the pleural cavity, which are filled with the lungs by breathing. Pleural sinuses (recessus pleurales) can be places of accumulation of serous or other fluid in diseases or lesions of the lung, pleura. The rib-diaphragmatic sinus (recessus costodiaphragmaticus) is located at the site of the transition of the rib pleura to the diaphragmatic one. Its maximum depth (9 cm) corresponds to the level of the middle axillary line. The diaphragm-mediastinapic sinus (recessus phrenicomediastindlis) is a shallow sagittally oriented cleft of the pleural cavity at the site of the transition of the lower part of the diaphragmatic pleura into the mediastinal cavity. The costal mediastinal sinus (recessus costomediastinalis) is a small gap located at the transition of the anterior rib of the rib pleura to the mediastinal.
The blood supply of the parietal is carried out by the vessels of the great circle of blood circulation. The rib pleura is provided with branches of the intercostal arteries, the mediastinal pleura - the pericardio-diaphragmatic artery, the diaphragmatic pleura - the upper diaphragmatic and muscular-diaphragm arteries.
The visceral pleura is supplied with blood from the system of bronchial arteries and the pulmonary artery.
Normally, the parietal and visceral leaves are separated by a very thin layer of liquid. It is established that, according to the law of transcapillary exchange Starling, normally the fluid moves from the capillaries of the parietal pleura to the pleural cavity, and then absorbed by the visceral pleura (Ligt, 1983).
[Topography of the pleura
The dome is located on the right and left 1.5-2 cm above the clavicle. The front and back borders of the parietal correspond to the boundaries of the right and left lungs. The lower border of the parietal pleura is located on one rib (2-3 cm) below the corresponding border of the lung. Passing down and lateral, the lower border of the rib pleura crosses the VII rib in the middle clavicular line, the VIII rib - along the anterior axillary, the IX rib - along the middle axillary, X - the back axillary, XI - along the scapula, and at the level XII the rib in the back border. The front borders of the right and left rib pleura extend from the II to IV ribs almost parallel to each other, and diverge at the top and bottom, forming interpleural fields. The upper interpleural field is turned top down, located behind the sternum handle. In this field there is a thymus. The lower interpleural field is triangular in shape, located behind the lower half of the sternum and the adjacent cartilage of the IV and V ribs. In the lower interpleural field, the anterior surface of the heart is covered with the pericardium to the anterior thoracic wall.
The pleura in the newborn is thin, loosely connected to the hilar fascia, mobile in respiratory movements of the lungs. Upper inter pleural space wide (occupied by large thymus). In the pleural cavity, with aging, adhesions (adhesions) appear between the parietal and visceral sheets of the pleura. The lower border in the elderly is slightly lower than at the age of 30-40.