9.5. Bronchial Blood Vessels
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There are two left bronchial arteries and one right bronchial artery. These will supply much of the lung parenchyma (i.e. the bronchi, conductive bronchioles and respiratory bronchioles). The bronchial arteries branch further, and each of these smaller branches can be described in relation to the bronchus that they are supplying, e.g. one tertiary bronchial branch will supply one tertiary bronchus. These branches eventually anastomose with the pulmonary arteries that surround the alveoli and alveolar ducts. The two left bronchial arteries (one superior bronchial artery and one inferior bronchial artery) normally arise directly from the ascending aorta, mainly at the level of T5 or T6. The right bronchial artery is slightly different. Remember from Section 4 that the third to eleventh posterior intercostal arteries and the subcostal (T12) artery arise from the descending aorta... well, the right bronchial artery arises from one of the right posterior intercostal arteries, normally the fifth or sixth posterior intercostal artery.
Remember also that the aortic arch crosses the anterior and lateral aspects of the trachea before being renamed the descending aorta, and travelling posterior to the left primary bronchus. So, the left bronchial arteries arise posterior to the bronchi and are often obscured when viewing the thorax from an anterior position.
The bronchial veins are divided into superficial and deep veins. The superficial veins are simply named the left and right bronchial veins. They drain the lung parenchyma surrounding the bronchi and the bronchioles. The right bronchial vein drains into the azygous vein (remember that the azygous vein runs only on the right side). The left bronchial vein drains into the superior hemi-azygous vein (which, if you remember from Section 4, drains into the azygous vein eventually). The azygous vein, at this level, drains into the superior vena cava. The deep bronchial veins drain deep lung parenchyma (e.g. alveoli) and often drain into the pulmonary veins.