The lung is a magnificent organ that performs a multitude of vital functions every second of our lives. Breathing is the most essential of these functions. With each breath, the lungs take in oxygen and remove carbon dioxide.

The air (oxygen) we breathe enters the lungs via the main windpipe (trachea), which branches into two main tubes supplying the right and left lung, respectively. These tubes progressively branch 22 additional times to form more than 100,000 smaller tubes (bronchi, bronchioles ) and more than 300 million air sacs ( alveoli ), which are only about 0.3 mm in diameter.

Thus, the surface area of the lungs is huge -- larger than the surface of a person's skin. In fact, if all the airways and air sacs of a person's lungs were laid flat on the ground, they would cover more than 100 square yards, which is larger than the size of a tennis court. Because the walls of these air sacs are 1/50th the thickness of tissue paper and are bathed with millions of tiny blood vessels called capillaries, there is an easy and efficient exchange of oxygen and carbon dioxide between the body and the environment.