The lungs receive blood from two sets of arteries. The pulmonary arteries follow the bronchi and ramify into capillary networks that surround the alveoli, allowing exchange of oxygen and carbon dioxide. The bronchial arteries derive from the aorta. They supply oxygenated blood to the tissues of the lung that are not in close proximity to inspired air, such as the muscular walls of the larger pulmonary vessels and airways (to the level of the respiratory bronchioles) and the visceral pleurae. The origin of the right bronchial artery is quite variable. It arises frequently from the third right posterior intercostal artery (the ﬁrst right aortic intercostal artery) and descends to reach the posterior aspects of the right main bronchus. It may arise from a common stem with the left inferior bronchial artery, which origi- nates from the descending aorta slightly inferior to the point where the left main bronchus crosses it. Or it may arise from the inferior aspect of the arch of the aorta and course behind the trachea to reach the posterior wall of the right main bronchus.
On the left side, two arteries are typically present, one superior and one inferior. The superior artery tends to arise from the inferior aspect of the aortic arch as it becomes the descending aorta. The inferior artery most often arises near the beginning of the descending aorta toward its posterior aspect. The left bronchial arteries come to lie on the posterior surface of the left main bronchus and follow the branching of the bronchial tree into the left lung.
Some of the more common variations of the bronchial arteries are shown in the lower part of the illustra- tion. The right bronchial artery and the inferior left bronchial artery may come from a common stem arising from the descending aorta. There may be only a single bronchial artery on the left. Supernumerary bronchial arteries may be present, going to either bronchus or both bronchi.
The majority of those who have studied the blood supply of the lungs seem to agree that precapillary anastomoses are present between the bronchial and pulmonary arteries, which can enlarge when either of these two systems becomes obstructed (an event that more commonly affects the pulmonary arteries). Whether these anastomoses are able to maintain full oxygenation of an involved area of lung has not been completely established but would seem likely given the surprisingly low rate of infarction in otherwise normal individuals who experience pulmonary embolism.
Branches of the bronchial arteries spread out on the surface of the lung beneath the pleura where they form a capillary network that contributes to the pleural blood supply.