Human Anatomy, Part 1 - K. A. Dyubenko, A. K. Kolomiysev, Y. B. Chaykovsky 2002

Special Part
Respiratory System, systema respiratorium [respiratory apparatus, apparatus respiratorius] - General Overview
Thoracic cavity, pleura, mediastinum

The thoracic cavity, cavitas thoracis, is the space bounded by the endothoracic fascia, fascia endothoracica. Inside the thoracic cavity lie the Lungs, covered by the Pleura, and the Mediastinum.

The pleura, pleura, is the serous membrane of the lungs, consisting of a Connective Tissue foundation covered with mesothelium. Two layers of the pleura are distinguished: the visceral (pulmonary) pleura and the parietal pleura, pleura visceralis (pulmonalis) et parietalis. The latter is subdivided into the mediastinal part, pars mediastinalis, which laterally bounds the mediastinum; the costal part, pars costalis, which lines the thoracic wall from the inside; and the diaphragmatic part, pars diaphragmatica. Near the lower edge of the ROOT of the lung, the visceral pleura transitions into the parietal pleura, forming a fold known as the pulmonary ligament, ligamentum pulmonale.

The slit-like space between the parietal and visceral pleurae is called the pleural cavity, cavitas pleuralis. In a healthy individual, this cavity is filled with 1-2 ml of serous fluid. In pathological conditions (such as Pleurisy), The amount of fluid increases significantly. This fluid is secreted by the free surface of mesothelial Cells (mesotheliocytes). Under normal conditions, mesotheliocytes are also responsible for the absorption of this fluid. In pathological states (pleurisy), the volume of fluid increases markedly because the secretion processes outweigh the absorption processes. Three slit-like spaces—known as pleural recesses, recessus pleurales—are formed between the various PARTS OF THE parietal pleura. The largest of these runs archwise between the costal and diaphragmatic pleurae, forming the costodiaphragmatic recess, recessus costodiaphragmaticus. The second lies sagittally between the diaphragmatic and mediastinal pleurae, forming the phrenicomediastinal recess, recessus phrenicomediastinalis. The third is positioned vertically between the costal and mediastinal pleurae, forming the costomediastinal recess, recessus costo-mediastinalis. The pleural recesses serve as reserve spaces into which the lungs expand during maximum inspiration. In pleurisy, fluid accumulates primarily in the pleural recesses and subsequently in the pleural cavity.

The level of the apices of the pleural sacs (the cupula of the pleura, cupula pleurae) corresponds to the level of the apices of the lungs.

The anterior border of the pleural sacs extends from the apices to the sternoclavicular joints. Further down on the right side, it runs to the midline at the level of the sternal angle, from where it descends to the level of the VI-VII Ribs and transitions into the lower border. On the left side, at the level of the VI rib, the anterior border deviates laterally, then descends to the VI rib, where it becomes continuous with the lower border.

The lower border on the right, along the linea medioclavicularis, crosses the VII rib; along the linea axillaris media, the IX rib; along the linea scapularis, the XI rib; and along the linea paravertebralis, the XII rib. On the left side, the lower border runs slightly lower.

The posterior border of the pleural sacs extends from the cupula to the XII rib along the linea paravertebralis.

The mediastinum, mediastinum, is a complex of Organs located between the mediastinal pleurae. Anteriorly, it is bounded by the anterior thoracic wall; posteriorly, by THE Vertebral Column, the necks of the ribs, and the prevertebral fascia; and inferiorly, by the Diaphragm. The mediastinum is divided into the superior mediastinum, mediastinum superius, and the inferior mediastinum, mediastinum inferius, which in turn includes the anterior mediastinum, mediastinum anterius; the middle mediastinum, mediastinum medium; and the posterior mediastinum, mediastinum posterius. The boundary between the superior and inferior mediastinum runs along a conventional horizontal plane passing through the upper margin of the roots of the lungs. The superior mediastinum contains the Thymus or its remnants, the ascending aorta and the aortic arch with its branches, the SUPERIOR VENA CAVA with its tributaries, the Trachea, the Esophagus, the Thoracic duct, sympathetic trunks, vagus nerves, phrenic nerves, and Lymph Nodes.

The anterior mediastinum is located between the body of the Sternum and the Pericardium (Fig. 295). It contains adipose tissue and extensions of the endothoracic fascia, within the layers of which lie the internal thoracic Arteries and Veins, retrosternal and anterior mediastinal lymph nodes. The middle mediastinum contains the pericardium enclosing The Heart, the tracheal bifurcation and main Bronchi, the pulmonary trunk, pulmonary arteries and veins, phrenic nerves accompanied by their pericardiophrenic vessels, and lymph nodes (Fig. 296). The posterior mediastinum is situated between the pericardium and tracheal bifurcation anteriorly and the vertebral column posteriorly. It includes the descending aorta, the azygos and hemiazygos veins, vagus nerves, sympathetic trunks and splanchnic nerves, the esophagus, the thoracic duct, and lymph nodes.