In the diagram below, which step represents the excretory function of the lungs?

By basic body biology, we inhale oxygen and we exhale carbon dioxide. The lungs are the organs that cause exhalation of carbon dioxide, which are then highly vital to our excretory system. Our lungs have tiny sacs called alveoli which remove carbon dioxide from our bloodstream as they enter our lungs, so our blood is only oxygen-rich as they leave the lungs.