Human Anatomy and Physiology - N. I. Fedyukovich 2003

Internal Organs
Respiratory System
Pleura and Mediastinum

The Pleura is a thin, smooth serous membrane that envelops each lung.

A distinction is made between the visceral pleura, which is tightly adherent to the lung tissue and extends into the fissures between the lung lobes, and the parietal pleura, which lines the inner walls of the thoracic cavity. At the hilum of the lung, the visceral pleura becomes continuous with the parietal pleura.

The parietal pleura consists of the costal, mediastinal, and diaphragmatic pleura. The costal pleura covers the inner surface of the Ribs and intercostal spaces; near the Sternum and posteriorly near THE Vertebral Column, it becomes continuous with the mediastinal pleura. Superiorly, the costal and mediastinal pleurae merge to form the dome of the pleura (pleural cupula), while inferiorly they transition into the diaphragmatic pleura, which covers the Diaphragm except for its central part where the diaphragm fuses with the Pericardium.

Thus, a slit-like closed space—the pleural cavity—is formed between the parietal and visceral pleurae. This cavity contains a small amount of serous fluid that lubricates the pleural layers during respiratory Movements of the Lungs. At the transitions of the costal pleura into the diaphragmatic and mediastinal pleurae, recesses known as pleural recesses (sinuses) are formed. These recesses serve as reserve spaces for the right and left pleural cavities, as well as reservoirs for the accumulation of pleural fluid in cases of impaired fluid production and absorption.

Between the costal and diaphragmatic pleurae lies the costodiaphragmatic recess; at the transition of the mediastinal pleura into the diaphragmatic, the phrenicomediastinal recess is located; and at the transition of the costal pleura into the mediastinal, the costomediastinal recess is formed.

The surface area of the parietal pleura is larger than that of the visceral pleura. The left pleural cavity is longer and narrower than the right. The superior border of the pleura extends 3— 4 cm above the I rib. Posteriorly, the pleura descends to the level of the HEAD of the XII rib, where it transitions into the diaphragmatic pleura. Anteriorly on the right side, the pleura runs from the sternoclavicular joint down to the VI rib, where it becomes the diaphragmatic pleura. On the left, the parietal pleura runs parallel to the right sheet of its pleura down to the Cartilage of the IV rib, then deviates to the left and transitions into the diaphragmatic pleura at the level of the VI rib. The inferior border of the pleura represents the line of transition from the costal to the diaphragmatic pleura. It crosses the VII rib along the midclavicular line, the IX rib along the midaxillary line, then runs horizontally, crossing the Х and XI ribs, and approaches the vertebral column at the level of the neck of the XII rib, where the inferior border merges into the posterior border of the pleura.

The Mediastinum is a complex of Organs located between the right and left pleural cavities. Anteriorly, the mediastinum is bounded by the sternum; posteriorly, by the thoracic spine; and laterally, by the right and left mediastinal pleurae. Superiorly, the mediastinum extends to the superior thoracic aperture, and inferiorly, to the diaphragm. The mediastinum is divided into two parts: the superior and inferior mediastinum.

The superior mediastinum contains the Thymus, the right and left brachiocephalic Veins, the SUPERIOR VENA CAVA, the arch of the aorta and the vessels arising from it (the brachiocephalic trunk, the left common carotid and subclavian Arteries), the Trachea, the upper part of the Esophagus, the corresponding sections of the Thoracic duct and of the right and left sympathetic trunks, as well as the vagus and phrenic nerves.

The inferior mediastinum contains the pericardium containing The Heart and great vessels, the main Bronchi, the pulmonary arteries and veins, Lymph Nodes, the lower part of the Thoracic Aorta, the azygos and hemiazygos veins, the middle and lower PARTS OF THE esophagus, the thoracic duct, the sympathetic trunks, and the vagus nerves.