Lung Disorders 135Inhaled air fl ows into the trachea in the throat, through the bron-
chial tubes, into the bronchioles, and fi nally into the air sacs. From
there it diffuses through the membranes of the air sacs into the blood
vessels lining the air sacs’ surface. The oxygen is then carried by the
blood vessels to the cells, where it’s used to produce energy and kill off
unfriendly substances such as cancer cells. The waste product from
energy production, carbon dioxide, takes the reverse route. Picked up
by the blood vessels in the intercellular fl uid surrounding the cells, it is
carried by the circulating blood to the same blood vessels encircling the
air sacs into which oxygen from the air sacs fl ows. Once inside the
alveolar sacs, carbon dioxide is expelled from the lungs.
In emphysema, the deterioration of the air sacs interferes with the
exchange of oxygen and carbon dioxide. Airborne pollutants such as
cigarette smoke and industrial exhaust eat up oxygen in the lungs, infl am-
ing the air sacs. Chronically infl amed air sacs eventually rupture and
combine to form large air pockets. The walls of these air pockets aren’t
permeable enough to enable the oxygen to diffuse into the surrounding
blood vessels. As a result, circulating blood, deprived of oxygen, is unable
to deliver enough oxygen to the cells. Moreover, the loss of elasticity in
the air sacs makes it impossible for the lungs to expel all the carbon
dioxide waste-product from cellular metabolism. So the CO 2 remains
trapped inside the alveoli, taking up space intended for oxygen.
The emphysema victim’s scarcely moving chest swells up with the
carbon dioxide that can’t be exhaled. The lungs are also overloaded
with oxygen that isn’t being absorbed into the circulating blood. What
happens to the cells that don’t receive enough oxygen to satisfy their
energy needs? They rob Peter to pay Paul, grabbing one oxygen atom
from each carbon dioxide molecule (CO 2 ), and in doing so, they turn
carbon dioxide into carbon monoxide (CO), a deadly compound, which
further damages the air sacs (alveoli) in the lungs.
Another source of the toxins that contribute to the destruction of the
alveoli in the lungs are metabolic wastes that the liver and kidneys are
too overworked to process. When the liver can’t detoxify poisonous gas
from the colon, the latter is carried by the blood out of the liver and
transported through the bloodstream to the lungs. The lungs become
a dumping ground for the kidneys as well. The gaseous wastes the kid-
neys can’t handle are also carried by the blood to the lungs. Processing
these metabolic wastes is hard on the lungs because they were designed