The respiratory system is the system by which oxygen, essential for life, is taken into the body and the waste product, carbon dioxide,
is expelled from the body. The respiratory system consists of the mouth and nose, airways and lungs.
Air enters through the mouth and nose and passes down the pharynx (throat) and through
the (voice box).
Air then continues down through the trachea (windpipe) which branches into two
bronchi (singular: Bronchus )
to each of the two lungs. The
of the bronchus is called .
The bronchi branch many times until becoming much smaller airways called "bronchioles".
At the end of each bronchiole
are tiny air-filled cavities called alveoli. Each alveolus is surrounded by many blood
oxygen to move
into the bloodstream and carbon dioxide out. This exchange of substances is the primary function of the
See also .