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Gaseous
exchange and breathing in mammals
Adrian
Whyte and Joanna Johnson, Contributor
FROM
OUR last article on respiration, recall
the following terms: Respiration is
a series of reaction which releases
energy from foods in all living cells.
Gaseous
exchange is the exchange of gases
at a respiratory surface.
In
mammals the respiratory surface for
gases is the alveolus of the lungs.
There are numerous alveoli air
sacs, supplied with gases via a system
of tubes (trachea, splitting into
two bronchi one for each lung
and numerous bronchioles) connected
to the outside by the mouth and nose.
The alveoli are air sacs found in
the walls of the lungs. Alveoli provide
a massive surface area through which
gases can diffuse. These gases diffuse
a very short distance between the
alveolus and the blood because the
lining of the lung and the capillary
are both only one cell thick.
(See
top diagram below)
| DIAGRAMS
OF THE RESPIRATORY SYSTEM |
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Breathing
is the mechanism in animals which
brings oxygen to a respiratory surface.
THE
PROCESS OF BREATHING OUT (EXPIRATION/EXHALATION)
1.
Internal intercostal muscles contract
causing the ribs and sternum to move
down and in.
2.
Diaphragm relaxes causing it to move
upwards.
3.
This causes:
*
The volume of the thorax and lungs
to decrease.
*
The pressure in the lungs to increase
causing the air pressure in the alveoli
to be more than the pressure in the
atmosphere.
*
Air is forced out (by the higher internal
pressure).
THE
PROCESS OF BREATHING IN (INSPIRATION/INHALATION)
1.
External intercostal muscles contract
causing the ribs and sternum to move
up and out.
2.
Diaphragm contracts causing it to
move down and flatten.
3.
This causes:
*
The volume of the thorax and lungs
to increase.
*
The pressure in the lungs to decrease
allowing the air pressure in the alveoli
to be less than the pressure in the
atmosphere.
*
Air is forced in (by the higher external
atmospheric pressure).
*
Adrian Whyte and Joanna Johnson
teach Biology at Ardenne High School
masterbio@gmail.com.
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