736
UNIT FIVE
DANGER! SECONDHAND SMOKE
E
xposure to environmental tobacco smoke (ETS)—also called
secondhand smoke—may be as dangerous as smoking. ETS
has two sources:
sidestream
smoke comes from lit cigarettes,
cigars, or pipes and
mainstream
smoke is exhaled by smokers.
The smoke contains more than 4,000 chemical compounds,
including irritants; carcinogens; mutagens; and many toxins, such as ben-
zene, formaldehyde, vinyl chloride, ammonia, arsenic, and cyanide.
An estimated 53,000 nonsmokers in the United States die each year from
ETS. That includes 46,000 heart disease deaths, 3,400 lung cancer deaths, and
1,900 to 2,700 infant deaths. In children, ETS is also responsible for hundreds
of thousands of cases of lower respiratory infections (bronchitis or pneumo-
nia), worsening asthma and ear infections, and low birth weight. One study
found that two-to-F
ve-year-olds absorb six times as much nicotine as older
children and have higher levels of biomarkers of vascular injury.
Even short exposures are dangerous, to anyone. Experiments that
exposed healthy nonsmokers to a room simulating a smoky bar showed
that just thirty minutes of breathing secondhand smoke activates platelets,
decreases coronary artery blood ±
ow, and produces heart rate variability—
all changes that raise the risk for cardiovascular disease. The normally
smooth endothelial inner lining of blood vessels becomes damaged, and
endothelial progenitor cells that typically travel to such injury sites from
the circulation are impaired. So not only are blood vessel linings damaged,
they cannot readily heal. The e²
ects on progenitor cells persist for at least
twenty-four hours.
The only way to decrease exposure to ETS is to eliminate it. Dividing a
space into smoking and nonsmoking areas is futile, because smoke lingers
for hours. This is why airplanes, restaurants, and many workplaces have been
made smoke-free. In areas where new laws ban smoking in bars, restaurants,
and workplaces, hospital admissions for heart attacks have dropped 20%.
The danger of secondhand smoke, long debated, is now widely accepted, and
new rules and regulations attempt to limit exposure.
19.1
INTRODUCTION
The respiratory system consists of passages that F
lter incom-
ing air and transport it into the body, into the lungs, and to
the many microscopic air sacs where gases are exchanged.
The entire process of exchanging gases between the atmo-
sphere and body cells is called
respiration
(res
pı˘-ra
shun).
It consists of several events:
Movement of air in and out of the lungs, commonly
called breathing, or
ventilation.
Exchange of gases between the air in the lungs and the
blood, sometimes called
external respiration.
Transport of gases by the blood between the lungs and
body cells.
Exchange of gases between the blood and the body
cells, sometimes called
internal respiration.
Oxygen (O
2
) use and production of carbon dioxide (CO
2
)
by body cells as part of the process of
cellular respiration.
19.2
WHY WE BREATHE
Respiration occurs on a macroscopic level—it is a function of
an organ system. However, the reason that body cells must
exchange gases—take up oxygen and release carbon dioxide—
is apparent at the cellular and molecular levels.
RECONNECT
To Chapter 4, Aerobic Reactions, pages 122–124.
Cellular respiration enables cells to harness energy
held in the chemical bonds of nutrient molecules. In aero-
bic reactions, cells liberate energy from these molecules by
removing electrons and channeling them through a series
of carriers called the electron transport chain. At the end of
this chain, electrons bind oxygen atoms and hydrogen ions
to produce water molecules. Without oxygen, these reac-
tions cease.
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