Smoker's Lung: Pathology Photo Essay (cont.)
How does emphysema come about?
Simply put, the cigarette smoke attracts inflammatory cells (white blood
cells, including neutrophils, lymphocytes, and macrophages) into the lung. Then,
the inflammatory cells release substances called proteases. The proteases
dissolve the proteins in the alveolar walls (septae) and thereby destroy the
septae. As a result, the alveoli join together (coalesce) to form the larger,
irregular, inefficient air sacs.
It turns out that about half of all smokers develop emphysema. Mild emphysema
is seen occasionally in non-smokers and may be due to passive smoking (exposure
to other people smoking) and industrial air pollution. Severe emphysema,
however, is seen only in smokers or in some people with rare inherited diseases
(e.g., alpha-1-antitrypsin deficiency). Still, it takes about 30 years of
smoking to develop fatal emphysema. This is because people usually don't die
from emphysema until more than 60% of the lung tissue is affected.
Why does smoker's lung look black?
The lung is connected and exposed by the airways to a potentially noxious
outside world. Accordingly, the alveolar spaces normally contain specialized
scavenger cells, called alveolar macrophages. The job of these macrophages is to
engulf (phagocytize) any possibly harmful foreign material that enters the lung
through the airways.
As you can imagine, cigarette smoke contains many impurities that are inhaled
in great numbers directly into the lung. For this reason, the alveolar spaces of
the smoker contain numerous scavenger cells (macrophages) that are filled with
engulfed (phagocytized) particles of impurities and debris, as illustrated in
Figure 5.
Figure 5: SCAVENGER CELLS IN SMOKER'S ALVEOLUS
Under the microscope, with this high magnification, you can actually see the
black and brown engulfed particles in the alveolar scavenger cells. Indeed,
smoker's lung may have so much of this particulate material that the lung
looks gray-black to the naked eye. So, most of the time, you don't need a
microscope to tell if someone is or was a heavy smoker. A naked eye examination
of a smoker's lung usually will reveal an enlarged gray-black lung with
enlarged air spaces (the emphysema, as you saw in Figure 4 and will see again in
Figure 8).
Next: What happens to the airways in chronic bronchitis? »
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