HUMAN BIOLOGY

the RespiRatoRy system 189

get rid of the accumulating debris. Eventually scar tissue
forms and can block parts of the respiratory tract.
In an otherwise healthy person, even acute bronchitis is
treatable with antibiotics. When inflammation continues,
however, scar tissue builds up and the bronchi become
chronically clogged with mucus. Also, the walls of some
alveoli break down and become surrounded by stiffer
fibrous tissue. The result is emphysema, in which the
lungs are so distended and inelastic that gases cannot be
exchanged efficiently (Figure 10.19). Running, walking,
even exhaling can be difficult. About 1.3 million people in
the United States have emphysema.
Emphysema is a type of chronic obstructive pulmonary
disorder, or CoPD. Smoking, frequent colds, and other
respiratory ailments sometimes make a person susceptible
to COPD. COPD can develop over 20 or 30 years. By the
time the problem is diagnosed, however, the lungs often
are permanently damaged.
asthma is a disorder in which the bronchioles suddenly
narrow when the smooth muscle in their walls contracts in
strong spasms. At the same time, mucus gushes from the
bronchial epithelium, clogging the constricted passages
even more. Breathing can become extremely difficult so
quickly that the victim may feel in imminent danger of
suffocating. Triggers include allergens such as pollen, dairy
products, shellfish, pet hairs, flavorings, or even the dung
of tiny mites in house dust. In susceptible people, attacks
also can be triggered by noxious fumes, cold air or water,
stress, strenuous exercise, or a respiratory infection. Afri-
can Americans have a greater risk of developing asthma.
While the reasons aren’t fully understood, the incidence of
asthma in the United States has grown rapidly in the last
several decades. Some health experts believe that increased
air pollution is at least partly to blame.
Many asthma sufferers rely on aerosol inhalers, which
squirt a fine mist into the airways. A drug in the mist
dilates bronchial passages and helps restore free breath-
ing. Some devices contain powerful steroids that can harm
the immune system, so inhalers should be used only with
medical supervision.

Figure 10.20 a mask that delivers pressurized air can prevent

episodes of sleep apnea.

malfunctioning breathing controls

cause apnea

As described in Section 10.6, breathing usually is on “auto-

pilot,” controlled by the brain’s respiratory center. In some

situations, however, a person can fail to breathe in the usual

pattern. In the interrupted breathing called apnea, breathing

stops briefly and then resumes spontaneously. During cer-

tain times in the normal sleep cycle, breathing may stop for

1 or 2 seconds or even minutes—in extreme cases, as often

as 500 times a night. This sleep apnea can be a contributing

factor in heavy snoring. Sufferers are not only tired during

the day; their risk of stroke and heart attack is increased

because apnea episodes cause a spike in blood pressure.

Sleep apnea is common in the elderly, because the

mechanisms for sensing a change in oxygen and carbon

dioxide levels gradually become less effective over the

years. Also, aging lungs become less elastic, so ventilation

becomes less efficient. Obese people often have a problem

with sleep apnea because fat deposits in the neck obstruct

the airways. For people with serious sleep apnea, wearing

a mask that delivers pressurized air is a common treatment

(Figure 10.20).

© Brian Chase/Shutterstock.com

Figure 10.19 Emphysema ravages the lungs. a Lung from

a person with emphysema. B Close-up of emphysema’s

damage in lung tissue. The black color is typical of

emphysema caused by smoking.

a

B

A: Southern Illinois University/Science Source;

B: Dr. E. Walker/Science Source

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