Question

All of the following statements about bronchial circulation are true, except:

• A. It contributes about 2% of systemic circulation
• B. It contributes to gaseous exchange
• C. It causes venous admixture of blood
• D. It provides nutritive function to the lung

Hint:

Bronchial circulation feeds lung tissue; which job actually belongs to the pulmonary circulation?

Answer 1

The Correct Option is B

Step 1: The lung has two circulations. The pulmonary circulation carries deoxygenated blood from the right ventricle and is responsible for gas exchange. The bronchial circulation is a small part of the systemic circulation that nourishes the lung tissue itself.

Step 2: Check each statement. The bronchial arteries carry about 1 to 2% of the systemic cardiac output, so option A is true. The bronchial circulation supplies oxygen and nutrients to the bronchi, bronchioles, connective tissue and pleura, that is its nutritive role, so option D is true.

Step 3: Part of the bronchial venous blood (which is deoxygenated systemic blood) drains into the pulmonary veins. This adds a small amount of poorly oxygenated blood to the freshly oxygenated pulmonary venous blood, producing a physiological venous admixture (one cause of the normal small alveolar to arterial oxygen difference). So option C is true.

Step 4: Gas exchange (oxygenation of venous blood) is the job of the pulmonary circulation across the alveolar capillary membrane, NOT the bronchial circulation. So saying the bronchial circulation contributes to gaseous exchange is false, and that is the except answer.

Answer: B. Contributes to gaseous exchange