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The Epic Interactive Encyclopedia 1998
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Epic Interactive Encyclopedia, The - 1998 Edition (1998)(Epic Marketing).iso
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Respiration
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1992-09-03
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Respiration is another name for breathing,
which we all do, all the time, on average 16
times per minute. On average, each breath
holds about 500ml of air, although the
maximum an adult pair of lungs can hold is
about 5 litres. Most parts of the body use
glucose as a source of energy. As glucose is
broken down by the body to make energy,
oxygen is used up, and a gas called carbon
dioxide is produced. Respiration has two
functions. The first is to provide oxygen for
the cells to use. The second is to remove the
carbon dioxide which the body produces. Both
of these processes take place in the lungs.
The lungs are like great sponges full of air
and blood. The gap between the air and the
blood is very small, only a few microns
thick, so that oxygen from the air can seep
into the blood (a process called diffusion)
and carbon dioxide from the blood can seep
out into the air, where it is breathed out.
These processes are happening side by side,
all the time. Control of respiration happens
in a part of the brain called the brainstem.
Oddly, the desire to breathe is provided, not
by lowering of the level of oxygen in the
blood, but by an increase in the level of
carbon dioxide. If you hold your breath for a
while, the discomfort you soon begin to feel
is due to the rising level of carbon dioxide
in your blood, not because the oxygen is all
used up. Air is drawn into the lungs through
a collection of tubes, the airways. The
largest of these is the trachea, or windpipe.
This divides into two main bronchi, one for
each lung. Each bronchus divides further into
many bronchioles, which split up into tiny
airways which supply the furthest parts of
the lung. The tiniest airways end in little
spaces called alveoli. Each alveolus is
surrounded by a network of fine blood
vessels, and it is here that the gas exchange
takes place. During respiration, air is drawn
into the lungs by movements of the diaphragm,
which is a muscular sheet which forms the
bottom of the chest cavity. When the
diaphragm contracts, it flattens and air is
sucked in. When it relaxes, air flows out by
the elastic recoil of the lungs. When extra
large breaths are needed, the whole rib cage
moves upwards and forwards, greatly
increasing the space inside the chest for air
to move into, and aiding the diaphragm in
drawing air into the lungs. Occasionally, the
diaphragm begins to twitch for no apparent
reason. When this happens, the result is
hiccups!
Subject by: Dr Aidan M. O'Donnell