Describe the pathway of oxygen getting from the air into the blood in the human body

diaphragm flattens and the chest wall moves up and out to decrease the pressure in the thorax. Inspiration occurs bringing air from the atmosphere into the mouth/nose and down the trachea, into the bronchi, bronchioles then the alveoli. The concentration of oxygen in the blood is lower than in the alveoli so it diffuses across the alveolar epithelium and the capillary epithelium into the arterioles.