The bronchial circulation:

D. All of the above.

DISCUSSION: The bronchial circulation is the primary blood supply for the conducting airways, pulmonary vessels, lymphoid tissue, and squamous cell carcinomas. In conditions such as mitral stenosis, bronchiectasis, or chronic obstructive pulmonary disease, the rich peribronchial venous network that drains the bronchial circulation may expand considerably, creating significant left-to-right shunts. Whenever the pulmonary artery circulation is obstructed, there is a tendency for bronchial circulation to increase; thus, the bronchial circulation is an important consideration during lung transplantation as well as in the surgical treatment of cyanotic congenital heart disease and chronic pulmonary embolism.