The
windpipe (trachea) joins the the the upper respiratory
tract to the lungs. If you gently touch the front of your throat you
can feel the trachea. The bottom of the trachea splits into two branches
called bronchi. One enters the right lung and one goes to the left lung.
The bronchial tree's job is to spread the air from the trachea over a very wide area as quickly as possible. The air passing through the windpipe divides into two branches. These divide into twigs called bronchioles. These twigs open into little bags called alveoli.
We have about 300 million alveoli (air sacs) in each lung. The alveoli gives our lungs a huge surface for absorbing oxygen from the air.