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How the Lungs Work
The lungs provide a very large surface area (the size of
a football field) for the exchange of oxygen and carbon dioxide
between the body and the environment.
A slice of normal lung looks like a pink sponge filled with
tiny bubbles or holes. These bubbles, surrounded by a fine
network of tiny blood vessels, give the lungs a large surface
to exchange oxygen (into the blood where it is carried throughout
the body) and carbon dioxide (out of the blood). This process
is called gas exchange. Healthy lungs do this very well.
Here is how normal breathing works:
- You breathe in air through your nose and mouth. The air
travels down through your windpipe (trachea) then through
large and small tubes in your lungs called bronchial (BRON-kee-ul)
tubes. The larger tubes are bronchi (BRONK-eye), and the
smaller tubes are bronchioles (BRON-kee-oles). Sometimes
the word "airways" is used to refer to the various tubes
or passages that air must travel through from the nose
and mouth into the lungs. The airways in your lungs look
something like an upside-down tree with many branches.
- At the ends of the small bronchial tubes, there are groups
of tiny air sacs called alveoli (al-VEE-uhl-EYE). The air
sacs have very thin walls, and small blood vessels called
capillaries run in the walls. Oxygen passes from the air
sacs into the blood in these small blood vessels. At the
same time, carbon dioxide passes from the blood into the
air sacs. Carbon dioxide, a normal byproduct of the body's
metabolism, must be removed.
The airways and air sacs in the lung are normally elastic—that
is, they try to spring back to their original shape after
being stretched or filled with air, just the way a new rubber
band or balloon would. This elastic quality helps retain
the normal structure of the lung and helps to move the air
quickly in and out. In COPD, much of the elastic quality
is gone, and the airways and air sacs no longer bounce back
to their original shape. This means that the airways collapse,
like a floppy hose, and the air sacs tend to stay inflated.
The floppy airways obstruct the airflow out of the lungs,
leading to an abnormal increase in the lungs' size. In addition,
the airways may become inflamed and thickened, and mucus-producing
cells produce more mucus, further contributing to the difficulty
of getting air out of the lungs.
In the emphysema type of COPD, the walls between many of
the air sacs are destroyed, leading to a few large air sacs
instead of many tiny ones. Consequently, the lung looks
like a sponge with many large bubbles or holes in it, instead
of a sponge with very tiny holes. The large air sacs have
less surface area for the exchange of oxygen and carbon dioxide
than healthy air sacs. Poor exchange of the oxygen and carbon
dioxide causes shortness of breath.
In chronic bronchitis, the airways have become inflamed
and thickened, and there is an increase in the number and
size of mucus-producing cells. This results in excessive
mucus production, which in turn contributes to cough and
difficulty getting air in and out of the lungs.
Most people with COPD have both chronic bronchitis and emphysema.
To read more about this and other lung diseases from the
National Heart, Lung and Blood Institute, please click here:
http://www.nhlbi.nih.gov/health/dci/Browse/Lung.html
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