The lungs

The Lungs
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.

The lungs are also important in the body's defense against infection and other harmful environmental factors. While the nose is the first line of defense against inhaled harmful materials, the lungs provide the second line of defense. Inhaled particles (smoke, pollution) or infectious agents (bacteria, viruses) pass through the mouth or nose and lodge in the lungs.

Mucus, a sticky fluid produced in the lungs, can trap these inhaled agents and aid the lungs' protective white blood cells (macrophages, neutrophils) in the engulfment and destruction of bacteria and other harmful materials. Coughing is the best way to clear mucus and other materials from the lungs; however, the larger airways have tiny hairlike cells called cilia that aid in this process. The cilia beat with a rhythm fast enough, and a force sufficient enough, to propel mucus and cells up the airways to be coughed out or swallowed. When a person smokes, the cilia are inactivated or destroyed, allowing thick mucus to accumulate and compromise lung defense.


This article was contributed by Dr. Dennis Doherty, co-chairman of the National Lung Health Education Program and Chief of Pulmonary and Critical Care Medicine at the University of Kentucky Medical Center. It provides a basic overview of the lungs and how they function -- information important to understanding the effects of COPD on this vital organ.