The bronchial veins are small vessels that return blood from the larger bronchi and structures at the roots of the lungs. The right side drains into the azygos vein

Azygos vein

The azygos vein is a vein running up the right side of the thoracic vertebral column. It can also provide an alternate path for blood to the right atrium by allowing the blood to flow between the venae cavae when one vena cava is blocked.-Structure:...

, while the left side drains into the left superior intercostal vein or the accessory hemiazygos vein

Accessory hemiazygos vein

The accessory hemiazygos vein is a vein on the left side of the vertebral column that generally drains the fifth through eighth intercostal spaces on the left side of the body.-Structure:...

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The bronchial veins are counterparts to the bronchial arteries. The bronchial veins, however, do not return all of the blood supplied by the bronchial arteries; much of the blood that is carried in the bronchial arteries is returned to the heart via the pulmonary veins.