Cambridge International A Level Biology Revision Guide

Cambridge International AS Level Biology
a
b
Figure 9.7 a Photomicrograph of normal lung tissue (× 75). b Photomicrograph of lung tissue from a person with emphysema,
showing large spaces where there should be many tiny alveoli (× 75).
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The loss of elastin makes it difficult to move air
out of the lungs. Non-smokers can force out about
4 dm 3 of air after taking a deep breath; someone with
emphysema may manage to force out only 1.3 dm 3 of air.
The air remains in the lungs and is not refreshed during
ventilation. Together with the reduced surface area for gas
exchange, this means that many people with emphysema
do not oxygenate their blood very well and have a rapid
breathing rate.
As the disease progresses, the blood vessels in the lungs
become more resistant to the flow of blood. To compensate
for this increased resistance, the blood pressure in the
pulmonary artery increases and, over time, the right side
of the heart enlarges.
As lung function deteriorates, wheezing occurs and
breathlessness becomes progressively worse. It may
become so bad in some people that they cannot get out
of bed. People with severe emphysema often need a
continuous supply of oxygen through a face mask to stay
alive. In Figure 9.7 you can see the destruction of alveoli
that occurs in emphysema. In Figure 9.8, you can compare
the appearance of diseased and relatively unaffected lung
tissue in a computerised tomography (CT) scan.
Chronic bronchitis and emphysema often occur
together and constitute a serious risk to health. The
gradual onset of breathlessness only becomes troublesome
when about half of the lungs is destroyed. Only in very
rare circumstances is it reversible. If smoking is given up
when still young, lung function can improve. In older
people, recovery from COPD is not possible. Over 60
million people worldwide have COPD. The WHO predicts
that COPD will become the third leading cause of death
worldwide by 2030.
There are legal controls in many countries on emissions
of pollutants from industrial, domestic and transport
fuels and on conditions in work places. Many countries
have also banned smoking in public places, such as shops,
restaurants and on public transport.
QUESTION
9.4 Summarise the changes that occur in the lungs of
people with chronic bronchitis and emphysema.
Figure 9.8 A CT scan of a horizontal section through the
thorax. The two black regions are the lungs. The right lung is
diseased with emphysema (blue-green areas). The left lung
is relatively unaffected at the level of this scan. You can see a
cross-section of a vertebra at the bottom of the scan.