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Unit 19: Biology Part 2 Page 60 of 137
Gases or liquids will always flow chest than outside of it, so air goes
from areas that have high pressure in.
to low pressure. If you’ve ever let
the air out of a balloon, you’ve Gas Exchange in the
seen this in action. The pressure Alveoli
inside the balloon is much higher
than the pressure outside the The process of gas exchange –
balloon. So, if the air can, it will oxygen going into the blood and
flow quickly out of the balloon. carbon dioxide leaving the blood to
be exhaled – also involves
differences in pressure, and is
actually very similar to inhalation
and exhalation. The amount, or
concentration, of oxygen in the air
found in alveoli is much greater
than it is in the blood that has just
come back from the cells of the
body. So, oxygen flows from the
alveoli to the blood, from high to
low concentration. Carbon dioxide
Figure 41 – The air pressure in is simply the opposite. The
a balloon is greater than the air concentration is higher in the blood
pressure outside a balloon, than in the air, so the flow goes
causing the air to flow out of it. from the blood to the alveoli.
A similar thing goes on in the
lungs. When you want to breathe
out, the diaphragm relaxes and
moves up, reducing the size of the
chest. The air pressure is higher in
the chest than outside, so air goes
out. This is called exhalation.
Breathing in, or inhalation, is the
reverse of this. The diaphragm
contracts and moves down, making
more space in the chest. Now the Figure 42 – The difference in
pressure becomes less inside the concentrations of carbon
dioxide (CO 2) and Oxygen (O 2)
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