The pleural cavity is the potential space between the two pleurae (visceral-parietal) of the lungs. The pleura is a serous membrane that folds back on itself to form a two-layer membrane structure. the thin space is known as the pleural cavity and contains a small amount of pleural fluid (a few milliliters in a normal human). the outer pleura is attached to the chest wall (1-9).
The pleural cavity helps the optimal function of the ears during respiration. it transmits chest wall movements to the lungs, particularly during heavy breathing. the closely-approved chest wall transmits pressures to the visceral pleural surface and thus to the lung (10-19).
In humans, there is no anatomical connection between the pleural cavities. the visceral pleura receives its blood supply from the bronchial circulation, and the parietal pleura receives its blood supply from the intercostal arteries. only in cases of pneumothorax (at simultaneous tension) can the contralateral parenchyma and blood vessels collapse. normally the visceral pleura slides over the parietal without sound or pain, but when the pleura is in action sounds can be auscultated. if the fluid then distends the cavity, the sounds disappear and the lung gradually moves toward the heart and the mediastinum toward the lung. ventilate the cavity, rupture of the lung when the elastic tissue of the lung recedes. the pleura crosses the rib in the region above the reflection.
The thoracic (inlet) structures consist of two groups. those of the median plane and those of each side closely related to the cervical parts of the pleurae and the lungs.
The thoracic outlet is wider transversely and slopes downward, thus the vertical extent of the cavity is longer. the diaphragm closes the opening and forms a convex floor for the cavity. centrally, it is flatter. the diaphragm descends towards the costal and vertebral attachments, thus the chest wall rapidly narrows downward (29-39).
The thoracic cavity is divided by the mediastinum. the heart is in the mediastinum, enclosed by the pericardium. the lungs occupy the left-right regions and the pleura covers the corresponding half of the thorax and forms the lateral limit of the mediastinum.
the upper part extends from the thoracic inlet through the lower border of the manubrium sternum. the lower part is subdivided into an anterior part of the pericardium. the pericardium contains the heart and juxtacardiac parts. It is posterior to the body of the sternum and anterior to thoracic vertebrae 5-8. consists of two opposite surfaces of serous membrane (fibrous pericardium-serous pericardium). the fibrous pericardium is compacted with fibrous collagenous tissue. the serous pericardium is a thin layer of flat mesothelial cells that blends with the fibrous pericardium and myocardial tissue.
The mediastinum is the partition between the lungs and includes the mediastinal pleura. It is commonly applied inside between the two pleural sacs, the sternum, and the thoracic spine that extends to the diaphragm.
The superior mediastinum is located between the manubrium sternum and the upper four thoracic vertebrae. it contains the ends of the sternohyoid, the colli muscles, the left common carotid, the brachiocephalic artery, and the aortic arch (32,39-48).
the anterior mediastinum which lies between the sternal body and the pericardium. it contains loose areolar tissue, the sternopericardial ligaments, sometimes part of the thymus gland, and the mediastinal branches of the internal thoracic artery.
The middle mediastinum contains the pericardium, ascending aorta, terminal azygos vein, both pulmonary veins, phrenic nerves, and tracheal bifurcation.
The posterior mediastinum is bounded in front by the tracheal bifurcation, the pericardium, and the superior surface of the diaphragm, and behind by the vertebral column. contains the thoracic aorta, vagus, azygos-hemiazygos vein, and thoracic duct.
Each lung is lined by a delicate serous membrane and the pleura, which is arranged in the investigated sac. a part of the serous membrane is submerged in the fissures between its lobes – the pulmonary pleura. the rest of the membrane lines cover the diaphragm, the parietal pleura. the two layers are continuous with each other around and below the root of the lung, the pleural cavity. the right and left pleural sacs are completely separate and touch each other for a short distance in front, in front of the 2nd and 3rd parts of the sternum, the interval between the two sacs – the mediastinum.
In the front of the thorax, where the parietal pleura is reflected back to the pericardium, the two pleural sacs are in contact. on the upper part of the chest they are separated by an angular interval. from this point the two pleura descend in close contact to the level of the fourth costal cartilage. the lower limit of the pleura is at a level considerably lower than the corresponding limit of the lung, but does not extend to the insertion of the diaphragm. therefore, the thin lower margin of the lung does not extend as low as the line of pleural reflection: the phrenocostal sinus.
The costomediastinal sinus is formed between the two layers of the pleura.
The line along which the right pleura is reflected from the checkerboard wall to the diaphragm begins anterior to and runs posterior to the seventh costal cartilage. the left pleural reflex follows the ascending part of the sixth cartilage and is lower than the right side. the right sac is shorter, wider, and reaches higher on the neck (figures 1, 22, 33, 44, 55, 66, 77, 88, 99, ,1010,,1111,,1212).
