Respiratory System
The respiratory
system brings air into the body and removes carbon dioxide. It includes the
nose, trachea, and lungs. When you breathe in, air enters your nose or mouth
and goes down a long tube called the trachea. The trachea branches into two
bronchial tubes, or primary bronchi, which go to the lungs. The primary bronchi
branch off into even smaller bronchial tubes, or bronchioles. The bronchioles
end in the alveoli, or air sac Oxygen follows this path and passes through
the walls of the air sac and blood vessels and enters the blood stream. At the
same time, carbon dioxide passes into the lungs and is exhaled.