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The respiratory system
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The respiratory system
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The nasal passages and lungs
Air is drawn into the body via the nose or mouth.
There are advantages to breathing through your nose:
the air is warmed so that it is closer to
body temperature
tiny hairs and mucus in the nose filter
the air, preventing larger dust and
pollen particles reaching the alveoli
mucus moistens the air, making it
easier for the alveoli to absorb.
Air then travels through the larynx, trachea (windpipe),
bronchi (one bronchus to each lung) and bronchioles to
the alveoli, where oxygen passes into the bloodstream.
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Mechanisms of breathing – inspiration
When you breathe in:
intercostal muscles between
the ribs contract, pulling the
chest walls up and out
Intercostal
muscles pull ribs
up and out
the diaphragm muscle
below the lungs contracts and
flattens, increasing the size of
the chest
the lungs increase in size,
so the pressure inside them
falls. This causes air to rush in
through the nose or mouth.
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Diaphragm
contracts and
moves down
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Mechanisms of breathing – inspiration
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Mechanisms of breathing – expiration
When you breathe out:
Ribs move in
and down
Intercostal muscles between
the ribs relax so that the chest
walls move in and down.
The diaphragm muscle below
the lungs relaxes and bulges up,
reducing the size of the chest.
Diaphragm
relaxes and
bulges up
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The lungs decrease in size, so
the pressure inside increases
and air is pushed up the trachea
and out through the nose or
mouth.
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Mechanisms of breathing – expiration
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Gas exchange at the alveoli
The alveoli are bunches
of tiny air sacks inside
the lungs.
Each individual sack is
called an alveolus.
When you breathe in,
they fill with air.
The alveoli are covered in tiny capillaries (blood vessels).
Gases can pass through the thin walls of each alveolus and
capillary, and into the blood stream.
Gases can also pass from the blood stream, into the alveolus.
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Gas exchange at the alveoli
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Composition of inhaled and exhaled air
Gas
Oxygen
Carbon dioxide
Nitrogen
Water vapour
Amount in
inhaled air
Amount in
exhaled air
21%
17%
Very small amount
3%
79%
79%
Small amount
Large amount
What are the main differences between
inhaled and exhaled air?
Why does mouth-to-mouth resuscitation work?
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Calculating minute volume
Remember:
Minute volume is the volume of air
you breathe in one minute.
You can calculate a person’s minute volume by multiplying
the volume of air they breathe in one breath, by their
respiratory (breathing) rate.
Question
If you breathe 14 times in one minute (respiratory rate)
and you breathe 0.5 litres in each breath, what is your
minute volume?
Answer:
Minute volume = 14 × 0.5 litres
= 7.0 litres
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Breathing during exercise
During exercise the muscle cells
use up more oxygen and
produce increased amounts of
carbon dioxide.
Your lungs and heart have to
work harder to supply the extra
oxygen and remove the carbon
dioxide.
Your breathing rate increases and
you breathe more deeply.
Heart rate also increases in order
to transport the oxygenated blood
to the muscles.
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Breathing during exercise
Muscle cell respiration increases – more
oxygen is used up and levels of CO2 rise.
The brain detects increasing levels of CO2 – a
signal is sent to the lungs to increase breathing.
Breathing rate and the volume of air in
each breath increase. This means that
more gaseous exchange takes place.
The brain also tells the heart to beat
faster so that more blood is pumped
to the lungs for gaseous exchange.
More oxygenated blood gets to the
muscles and more CO2 is removed.
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Breathing changes during exercise
Look at these statistics for a 16 year-old athlete:
During rest
Respiratory rate
Volume per
breath
Minute volume
During exercise
14 breaths/ minute 32 breaths/ minute
0.4 litres
2.4 litres
?
?
Calculate the athlete’s minute volumes
during rest and exercise.
Rest minute volume = 5.6 litres
Exercise minute volume = 76.8 litres
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The effects of exercise on lung structures
In the long-term, regular exercise strengthens
the respiratory system.
The respiratory muscles (the
diaphragm and intercostals) get
stronger, so they can make the
chest cavity larger.
This larger chest cavity means
more air can be inspired, therefore
increasing your vital capacity.
More capillaries form around the alveoli,
so more gaseous exchange can take place.
Gas exchange can now take place more
quickly meaning exercise can be maintained
at a higher intensity for longer.
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Respiration
Respiration is the process that takes place in living
cells which releases energy from food molecules.
Glucose from food is used to fuel exercise.
Oxygen is required to ‘break down’
the glucose to produce energy.
This energy is used to make
muscles contract.
respiration
energy
glucose
oxygen
Waste products,
including carbon dioxide,
are produced as a result of
the chemical reactions. These
must be removed and excreted.
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Aerobic respiration
There are two different types of respiration.
When you exercise at a steady, comfortable rate, the
cardiovascular system is able to supply the muscles with
all the oxygen they need.
Under these conditions, aerobic respiration takes place.
glucose + oxygen
energy +
carbon
+ water
dioxide
Aerobic exercise can be maintained for long periods
without the performer getting breathless or suffering
muscle cramps. Moderate activities like walking,
jogging, cycling and swimming use aerobic respiration.
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Aerobic respiration
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