Question

An increase in PCO2 of expired air causes bronchioles to _______. A decrease in the PCO2 of expired air causes bronchioles to _____.

Option 1: Constrict
Option 2: Dilate
Option 3: Remain unaffected
Option 4: Reverse direction

Answer 1

An increase in PCO2 of expired air causes bronchioles to dilate. A decrease in the PCO2 of expired air causes bronchioles to constrict.

Step-by-step explanation:

Ventilation is regulated by the diameter of the airways, whereas perfusion is regulated by the diameter of the blood vessels. The diameter of the bronchioles is sensitive to the partial pressure of carbon dioxide in the alveoli. A greater partial pressure of carbon dioxide in the alveoli causes the bronchioles to increase their diameter as will a decreased level of oxygen in the blood supply. This allows carbon dioxide to be exhaled from the body at a greater rate. On the other hand, a greater partial pressure of oxygen in the alveoli causes the pulmonary arterioles to dilate, increasing blood flow.