The main goal of the respiratory system is to bring fresh in so that you can extract oxygen from it, and blow used air out so that you can rid of carbon dioxide which is the end product of carbon metabolism inside our bodies.

呼吸系统的主要功能是,吸入新鲜空气,以便获得空气中的氧气,呼出废气,以便排出二氧化碳,二氧化碳是人体内碳代谢的终产物

耶鲁公开课 - 生物医学工程探索课程节选