We inhale oxygen at the nose.  Then the air travels into the pharynx. The air then travels to the larynx, or voice box. The oxygen now travels into the trachea, or what we call the windpipe. The trachea splits into two tubes called the bronchi, the air then travels into it. One tube goes to each lung and branches into thousands of tiny sacs called bronchioles. Once inside the lungs, oxygen goes into the little sacs called alveoli, which are covered with capilleries that cover them.  The capillaries then bring oxygen into the bloodstream, where it is delivered to other systems