Mechanisms of breathing 1
Mechanisms of breathing
Mechanisms of breathing 2
What you will learn about
in this topic:
1. The function of the respiratory
system
2. The mechanisms of breathing
3. The role of the lungs
4. Alveoli
5. Composition of air inhaled and
exhaled
Mechanisms of breathing 3
Learning objectives
By the end of this presentation you
should be able to:
• Understand the function of the
respiratory system
• Describe the effects of exercise on
breathing
• Explain what happens when you
breathe
Mechanisms of breathing 4
The function of the
respiratory system
The function of the respiratory
system is to get oxygen into the
body and carbon dioxide and waste
products from metabolism out of the
body.
Mechanisms of breathing 5
This happens through the act of
breathing. Breathing in (inhalation)
gets the oxygen in, so it can be
used by the body to release energy.
Breathing out (exhalation) removes
the carbon dioxide so it does not
build up and poison the body.
Mechanisms of breathing 6
The following are all parts of the
respiratory system:
• Air passages
• Lungs
• Diaphragm
Mechanisms of breathing 10
Composition of inspired
and expired air
The air we breathe in is very
different from the air we breathe
out.
The parts that make up inhaled and
exhaled air are called its
composition.
Mechanisms of breathing 11
Percentage of air inhaled:
0.5%
0.5%
20.0%
Key
■ Nitrogen
■ Oxygen
■ Carbon dioxide
■ Other
79.0%
Mechanisms of breathing 12
Percentage of air exhaled:
4.0%
1.0%
16.0%
Key
■ Nitrogen
■ Oxygen
■ Carbon dioxide
■ Other
79.0%
Mechanisms of breathing 13
The link between respiration
and circulation
Oxygen goes from the respiratory
system to the circulatory system
and then back to the respiratory
system.
Mechanisms of breathing 14
Oxygen breathed
in goes through
the mouth or
nose, down the
trachea, into the
lungs and into
the alveoli.
Mechanisms of breathing 15
Oxygen then passes through the
alveoli walls into the red blood cells,
via the capillaries.
Oxygen joins with haemoglobin to
make oxyhaemoglobin.
The oxyhaemoglobin is used by the
working body and is transported by
the circulatory system to cells
needing to release energy.
Mechanisms of breathing 16
Carbon dioxide is produced as a
waste product. This is converted
into a gas and passes back through
the alveoli walls, via the capillaries
into the blood plasma.
The carbon dioxide passes through
the capillary and alveoli walls into
the alveoli. It is then exhaled from
the body.
Mechanisms of breathing 17
Parts of the respiratory system
Mechanisms of breathing 18
The mechanism of breathing
Lungs are not muscle, cannot move
of their own accord and are not
controlled by the central nervous
system.
The key to breathing is the
diaphragm and the intercostal
muscles between the ribs.
Expiration
Mechanisms of breathing 19
When we breathe in (inspiration)
the following happens:
• The diaphragm pulls down
• The intercostal muscles contract
• Air pressure is reduced
• Air is sucked through the tubes
into the lungs
• The chest expands.
Mechanisms of breathing 20
Mechanisms of breathing 21
When we breathe out (expiration)
the opposite happens:
• The diaphragm relaxes into its
dome position
• The intercostal muscles relax
• The chest becomes smaller
• Pressure increases in the lungs
• Air is forced out
Mechanisms of breathing 22
Mechanisms of breathing 23
Task 1
In groups of four, write 13
statements on 13 pieces of card
(one on each card) about the route
of oxygen and carbon dioxide
around the body.
Put your cards in order, starting
and ending with a card marked
‘Oxygen is inhaled’.
Mechanisms of breathing 24
Possible answers to Task 1
• Oxygen passes through the larynx
and trachea.
• Oxygen arrives in the lungs via
the bronchi and bronchioles.
• Oxygen passes to the alveoli and
transfers to the haemoglobin
through the plural membrane
Mechanisms of breathing 25
• The haemoglobin in the red blood
cells binds with the oxygen to
become oxyhaemoglobin.
• The blood travels through the
pulmonary vein to the left side of
the heart.
• The heart pumps the blood through
the aorta to the arteries.
• The arteries carry the oxygenated
blood around the body.
Mechanisms of breathing 26
• The haemoglobin releases the
oxygen at the muscles and
collects the carbon dioxide; the
blood is now considered
deoxygenated.
• The veins carry the deoxygenated
blood.
• The deoxygenated blood arrives
at the heart.
Mechanisms of breathing 27
• The heart pumps the
deoxygenated blood back to the
lungs via the pulmonary artery.
• The carbon dioxide passes across
the pleural membrane and into
the alveoli.
• The carbon dioxide passes
through the trachea and is
exhaled.
Mechanisms of breathing 28
The role of the lungs
The lungs are
positioned inside
the chest cavity
and are protected
by the ribcage.
Mechanisms of breathing 29
The action of breathing means that
the lungs are constantly moving in
and out. To protect them from any
friction due to the movement, the
pleural membrane forms a complete
lining around them.
The pleural membrane is smooth
and has a moist, slimy mucus.
Mechanisms of breathing 30
Alveoli
Alveoli are tiny
air sacs at the
end of the
bronchioles.
Mechanisms of breathing 31
There are millions of them that
allow gases to exchange inside
them.
Oxygen passes across the pleural
membrane and into the blood.
Carbon dioxide passes from blood to
the alveoli.
Mechanisms of breathing 32
Here is a simplified version of what
happens:
• Oxygen from the air breathed in
enters the circulatory system to
be used by the working muscles.
Mechanisms of breathing 33
• Carbon dioxide, which is toxic to
the system, transfers from the
used blood, out of the circulatory
system, back into the alveoli, to
be breathed out along with
oxygen, water and nitrogen.
Mechanisms of breathing 34
• The capillaries, covering the
surface of the alveoli, link the
respiratory system with the
circulatory system.
• Regular exercise conditions the
lungs to excrete more of the
carbon dioxide from the body.
Mechanisms of breathing 35
Tidal volume is the amount of air
breathed in and out of the body
during normal breathing.
During exercise, the volume is
forced to change. It is then called
forced breathing.
Mechanisms of breathing 36
Vital capacity is the largest
amount or volume of air that can be
exhaled after the largest possible
inhalation.
Residual volume is the amount of
air that, even after as much air as
possible has been exhaled, is left in
the lungs.
Mechanisms of breathing 37
Task 2
In groups of four, describe the
action of breathing using the
following words to help you:
• Nose
• Mouth
• Trachea
• Lungs
• Ribs
• Intercostal
muscles
• Diaphragm
Mechanisms of breathing 38
Possible answers to Task 2
From the nose or mouth, air enters the trachea and
moves towards the lungs.
The trachea divides into two branches called the
bronchi. These sub-divide into smaller tubes called
bronchioles.
During heavy exercise the body uses the intercostal
muscles between the ribs to aid the diaphragm in the
exhalation of air from the lungs.
At the end of the bronchioles are alveoli.
Alveoli are air sacs with many tiny blood vessels called
capillaries running from them.
Mechanisms of breathing 39
Exam questions
1. Explain the process of
inspiration.
2. Explain the process of
expiration.
Mechanisms of breathing 40
What you have learnt about
in this topic:
1. The function of the respiratory
system
2. The mechanisms of breathing
3. The role of the lungs
4. Alveoli
5. Composition of air inhaled and
exhaled
Mechanisms of breathing 41
Learning objectives
You should now be able to:
•Understand the function of the
respiratory system
•Describe the effects of exercise
on breathing
•Explain what happens when you
breathe