When you breathe, the airway (respiratory) system supplies oxygen to your blood. Then your blood takes oxygen to all parts of the body.

The nose, mouth, throat (pharynx and larynx), and hollow spaces in the cheeks and around the eyes (sinuses) make up the upper respiratory tract. The trachea (windpipe), breathing tubes (bronchial tubes), bronchioles, and air sacs (alveoli) of the lungs make up the lower respiratory tract.