During respiration oxygen enters the lungs and diffuses from there into the bloodstream. The muscles surrounding the ribcage cause compression on the lungs to enable it to empty (exhale) and fill (inhale). The carbon dioxide from the process exits the body via the exahale. The path of the air is: nasal cavity, pharynx, trachea, primary bronchi, seoncary bronchi, teritary bronchi, bronchioles, and finally alveoli (which is where the gas exchange takes place). This exchange of gas happens via diffusion.
