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The
ACADEMY
of
NUTRITION & SUCCESS
Nutrition
The Respiratory System
We live in a world of air, and each and every cell in
the body communicates with the atmosphere by way
of the lungs. What they must receive is oxygen.
In the beginning,
there was less oxygen
in the air than there
is today. Oxygen is
produced by plants
through a process
known as photosynthesis. In this process,
plants use the energy
of the sun to create
sugars (their food
source) from carbon
dioxide in the air and
water in the soil. The
by-product is oxygen.
Also in the beginning, there were fewer plants, but as
plant life flourished, the oxygen level rose, until now
it makes up about 21 percent of the air.
It is converted back
into carbon dioxide
by mammals, like humans. Where this conversion takes place is
in the lungs.
It’s easy to think of
lungs like inflatable
balloons, each essentially a hollow vessel that is filled up with air each
time we breathe. In fact, if you were to cut through a
section of lung, you would find it isn’t hollow at all,
but rather, it resembles a fairly dense sponge.
There is a pair of lungs in most mammals. In hu-
mans, the right lung has three main compartments and
is larger than the left lung, which has two. Neither has
any muscle tissue. Air is drawn into the lungs by a
slight vacuum, a lower atmospheric pressure than that
which surrounds the lungs. When the muscles of the
chest cavity expand, the vacuum makes the lungs expand, and air is pulled in. When the muscles contract,
the air is expelled. The lungs themselves don’t play
an active role in the process.
The air enters through the passages in the mouth
and nose, which funnel the air into the windpipe, a
four-inch tube leading to the lungs. This is an important process because the air must be warmed, moistened, and filtered before it reaches the lungs. As the
air reaches the lungs, the windpipe branches into two
parts, one leading to the right lung, the other to the
left.
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The
ACADEMY
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From here the air follows increasingly smaller and
smaller branches. First it passes through the bronchi,
then the smaller bronchioles, which are only 1/100 of
an inch thick.
Nutrition
cells attach it to hemoglobin to be delivered throughout the body.
It actually isn’t a very efficient system. Although
oxygen makes up about 21 percent of the air, only
slightly more than 4 percent of that oxygen is passed
to the red blood cells during each breath. In other
words, the air you exhale still has nearly 17 percent
oxygen. In addition, we rarely even come close to using the lungs’ full capacity. The lungs can hold a total
of about 8 pints of air, yet during each breath we can
only draw in about one pint.
Air transferring into the blood in the alveoli
It is when the air reaches the alveoli that the action really begins. These tiny sacs are where oxygen
is transferred to the blood for circulation around the
body and carbon dioxide is passed from the blood to
the lungs to be expelled. Each alveolus is covered in
a cobweb of tiny blood capillaries. So dense is this
contact that in an adult the alveoli number in the hundreds of millions, with more than 100 yards of total
surface area.
Across this surface area pass red blood cells, oneby-one, and single-file through the capillaries. Here,
contact takes place across the fine membrane of the
lung, and the single-cell walls of the capillaries. And
the exchange of gases takes place. The process is
physical, and automatic. Gases with lower concentration in solution diffuse to either side of the permeable
membrane that separates the blood and the air. Since
the concentration of oxygen in the lung is higher
(compared to the un-oxygenated blood), it flows to
the area of lesser concentration where the red blood
Still, the system is efficient enough. While we are
lying still, we need about 8 pints of air per minute.
Sitting working at a desk raises the requirement to 17
pints per minute. Walking requires 24 pints per minute, and a fast run requires 50 pints per minute. Thus,
as our activity increases, both the rate at which we
breathe and the depth of our breaths increase. The air
in the lungs is exchanged successively, although we
never quite rid ourselves of all the last breath; a liter
of air is always in the lungs, even after a maximum
exhalation.
The regulation of breathing is a highly complex
process. Partly it is triggered by
chemical stimulation when the
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The
ACADEMY
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Nutrition
NUTRITION & SUCCESS
respiratory center in the brain detects rising levels
of carbon dioxide in the bloodstream. However, this
basic process has an override. In cases where we are
nervous or scared, other areas of the brain can act on
the breathing center, speeding up the rate at which
we take in air even if there isn’t a heightened level of
carbon dioxide. And of course, we can also consciously
override the entire breathing response, like when we
hold our breath (this only works temporarily however;
before the carbon dioxide levels get high enough to
cause fainting, the automatic respiration system will
force breathing to resume.)
The lungs are subject to a number of abuses. At
birth, each of us has bright pink lungs, with no contaminants. As we age, exposure to dust and pollutants
in the air causes a build-up of some of this matter in
our lungs. People living in large cities, in particular,
have large darkened areas of their lungs by the time
they reach adulthood.
Fortunately, the lung is a resilient organ. Smokers
who quit before the age of thirty still have time for
their lungs to regain their original level of efficiency.
However, any smoker that quits at any age will eventually overcome smoker’s hack—plus reduce the possibility of contracting cancer.
As for the pollution in the air, indoor air filters
provide a measure of protection, and avoiding
polluted air outside will help you keep your lungs
relatively clean. That and getting regular exercise
should keep the lungs breathing freely for many years
in the future.
Test your knowledge
Smoking illustrates what prolonged exposure to
pollutants does to the lungs. The persistent hacking
cough of smokers is caused by overactive mucus
membranes that attempt to moisten the lungs to prevent further damage from the searing smoke. This
mucus, in turn, drips into the alveoli. In essence, the
smoker’s hack is the lungs’ way of preventing drowning. With no other mechanism to clear the extra mucus, coughing is the only way to keep the alveoli
clear.
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