Development and Anatomy

Bronchial vessels--Bronchial arteries (or major aortico-pulmonary collaterals) arise variably from the descending aorta and the intercostals, or sometimes from the subclavian or internal mammary arteries. They supply the trachea and airways to the level of the terminal bronchioles. Bronchial arteries also supply the visceral pleura, hilar lymph nodes, and walls of large pulmonary arteries and veins. They are smaller than pulmonary arteries, anastomose with the pulmonary arteries distally, and have medias with an internal elastic layer. Intrapulmonary bronchial arteries and veins are located in the subepithelial tissue of the airway. Intrapulmonary bronchial veins drain into the pulmonary veins and left heart. Extrapulmonary bronchial veins drain into systemic veins and the right heart [11].

The above photo shows cartilage at the right, bronchial artery at the center, and lumen at upper left (elastic stain).

Pleura--The pleura, shown here (elastic van Gieson stain), has a simple mesothelial layer of flat to cuboid cells (not seen in this section). Epithelium rests on a thin subepithelial layer [12]. External and internal elastic layers delimit a fibrovascular layer containing bronchial arteries, veins, and lymphatics. The inner elastic layer is continuous with the elastic tissue of alveolar walls. An elastic tissue stain showing disruption of the elastic layers by tumor helps to determine if the tumor has invaded the pleura.

Lymphatics--Lymphatics that anastomose with each other are found in the bronchovascular bundle as far as the terminal bronchiole, in the interlobular septa, and in the pleura [4]. They are absent from the alveolar walls. In contrast to veins, lymphatics have valves, as shown in the photo (arrow). Lymph flow is thought to be toward the hilum. In pulmonary interstitial emphysema of infancy, air that gains access to these channels can dissect widely. Lymph nodes have been found in 6 to 20% of lungs. They may appear as small, discrete nodules, radiographically.