The bronchial arteries (Fig. 3.49) and veins constitute the “nutritive” vascular system of the pulmonary tissues (bronchial walls and glands, walls of large vessels, and visceral pleura). They interconnect within the lung with branches of the pulmonary arteries and veins.
The bronchial arteries originate from the thoracic aorta or one of its branches:
A single right bronchial artery normally arises from the third posterior intercostal artery (but occasionally, it originates from the upper left bronchial artery).
Two left bronchial arteries arise directly from the anterior surface of the thoracic aorta—the superior left bronchial artery arises at vertebral level TV, and the inferior one inferior to the left bronchus.
The bronchial arteries run on the posterior surfaces of the bronchi and ramify in the lungs to supply pulmonary tissues.
The bronchial veins drain into: either the pulmonary veins or the left atrium, and into the azygos vein on the right or into the superior intercostal vein or hemiazygos vein on the left.
Structures of the lung and the visceral pleura are supplied by visceral afferents and efferents distributed through the anterior pulmonary plexus and posterior pulmonary plexus (Fig. 3.50). These interconnected plexuses lie anteriorly and posteriorly to the tracheal bifurcation and main bronchi. The anterior plexus is much smaller than the posterior plexus.
Branches of these plexuses, which ultimately originate from the sympathetic trunks and vagus nerves, are distributed along branches of the airway and vessels.
Visceral efferents from: the vagus nerves constrict the bronchioles; the sympathetic system dilates the bronchioles.
Superficial, or subpleural, and deep lymphatics of the lung drain into lymph nodes called tracheobronchial nodes around the roots of lobar and main bronchi and along the sides of the trachea (Fig. 3.51). As a group, these lymph nodes extend from within the lung, through the hilum and root, and into the posterior mediastinum.
Efferent vessels from these nodes pass superiorly along the trachea to unite with similar vessels from parasternal nodes and brachiocephalic nodes, which are anterior to brachiocephalic veins in the superior mediastinum, to form the right and left bronchomediastinal trunks. These trunks drain directly into deep veins at the base of the neck, or may drain into the right lymphatic trunk or thoracic duct.
The mediastinum is a broad central partition that separates the two laterally placed pleural cavities (Fig. 3.55). It extends: from the sternum to the bodies of the vertebrae, and from the superior thoracic aperture to the diaphragm (Fig. 3.56).
The mediastinum contains the thymus gland, the pericardial sac, the heart, the trachea, and the major arteries and veins.
Additionally, the mediastinum serves as a passageway for structures such as the esophagus, thoracic duct, and various components of the nervous system as they traverse the thorax on their way to the abdomen.
For organizational purposes, the mediastinum is subdivided into several smaller regions. A transverse plane extending from the sternal angle (the junction between the manubrium and the body of the sternum) to the intervertebral disc between vertebrae TIV and TV separates the mediastinum into the: superior mediastinum, and inferior mediastinum, which is further partitioned into the anterior, middle, and posterior mediastinum by the pericardial sac.
The area anterior to the pericardial sac and posterior to the body of the sternum is the anterior mediastinum. The region posterior to the pericardial sac and the diaphragm and anterior to the bodies of the vertebrae is the posterior mediastinum. The area in the middle, which includes the pericardial sac and its contents, is the middle mediastinum (Fig. 3.57).