We expel our carbon dioxide. So our lungs are specialized organs that are responsible for carrying out this process of breathing. So inside our lung, inside the lungs, we have many tiny microscopic, specialized saclike structures we call alveoli. And these alveoli are specialized in exchanging oxygen for carbon dioxide. And the lungs ultimately expelled that carbon dioxide to the outside of our body, to the outside environment. Now, the question we're going to explore and answer in this lecture is how the process of breathing, how the process of ventilation actually takes place inside our lungs.