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The pulmonary arteries are unusual in so much as they carry unoxygenated, venous blood. The main pulmonary artery that emerges from the right ventricle is termed the pulmonary trunk. The anatomy of the division of the trunk and main branches is discussed in the submenu.
Once the respective pulmonary artery reaches the lung parenchyma, it divides up in tandem with the bronchial tree. Each lobar bronchus, segmental bronchus and lobular bronchus has a separate branch of the respective main pulmonary artery. The artery mirrors the bronchus by entering each division of lung in a roughly central position e.g. at the hilar apex of each bronchopulmonary segment. The artery tends to be sited on the posterior aspect of the respective bronchus.
The pulmonary arteries eventually subdivide into capillaries which are essential to gaseous exchange and also nourish the alveoli but not the bronchi. The bronchi are supplied by the bronchial circulation. There is a small amount of anastomosis between bronchial and pulmonary circulations at the level of the capillaries.