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

Carbon dioxide moves from the circulatory system to the respiratory system primarily in the lungs, specifically at the alveoli. In the alveoli, carbon dioxide diffuses from the blood in the capillaries into the air sacs due to the concentration gradient, where it is then exhaled. This exchange occurs as oxygen from the inhaled air moves in the opposite direction, entering the bloodstream.