M/C

Any action which causes the ____________ to move ____________ results in inhalation of air into the lungs.
A.the floor of the thoracic cavity; upward
B. the sternum; downward
C. the lateral walls of the thoracic cavity; inward
D. the sternum; upward
E. the ribs; downward


Perfusion/ventilation balancing in the lungs is accomplished by two reflexive mechanisms: bronchoconstriction in response to low alveolar Pco2, and
A. bronchodilation in response to high alveolar Po2 levels.
B. vasoconstriction of pulmonary arterioles in response to low alveolar Po2.
C. vasoconstriction of pulmonary arterioles in response to high alveolar Po2.
D. vasoconstriction of pulmonary arterioles in response to low alveolar Pco2.
E. vasodilation of pulmonary arterioles in response to high alveolar Pco2.

I'm guessing (B)... Not too sure. Here's my responsing:

The effects of carbon dioxide on blood vessels varies in the systemic circulation and pulmonary circulation. In the respiratory system, an area of high CO2 indicates low ventilation, since the CO2 cannot be expelled. In order to divert blood from areas of low ventilation, vasoconstriction occurs. However in the periphery, CO2 causes vasodilation, in order to increase the amonut of blood (containing nutrients and vital oxygen) to the body's tissue.

What are your thoughts?