Where does carbon dioxide move from the circulatory system to the respiratory system apex?

The answer is Alveoli.  Carbon dioxide move from the circulatory system to the respiratory system in the Alveoli.  Alveoli are tiny sacs within our lungs that allow oxygen and carbon dioxide to move between the lungs and bloodstream. The function of the alveoli is to get oxygen into the blood stream for transport to the tissues, and to remove carbon dioxide from the blood stream.

Ibelieve this would be an obstacle.