KS4 Physical
Education
The Respiratory System
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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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Measuring breathing
Tidal volume is the amount you breathe
in and out in one normal breath.
Respiratory rate is how many
breaths you take per minute.
Minute volume is the volume of air
you breathe in one minute.
Vital capacity is the maximum volume of air you can
breathe out after breathing in as much as you can.
Residual volume is the amount of air left in your lungs
after you have breathed out as hard as you can.
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Measuring breathing
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Measuring breathing
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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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Anaerobic respiration
When you exercise at a high intensity, the cardiovascular
system cannot supply enough oxygen to the muscles.
Under these conditions, anaerobic respiration takes place.
glucose
energy + lactic acid
With no oxygen available, glucose is burned to produce
energy and lactic acid.
Lactic acid is a mild poison. As it builds up, it causes muscle
pain and eventually cramp.
Short, intense activities like sprinting, weightlifting, jumping
and throwing use anaerobic respiration.
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Oxygen debt
After anaerobic activity, oxygen is
needed to neutralize the lactic acid.
This is called an oxygen debt. It is
repaid after exercise.
The oxygen reacts with the lactic
acid to form CO2 and water.
Rapid and deep breathing is needed
for a short period after high intensity
exercise in order to repay the debt.
This also helps to remove the
carbon dioxide which accumulates
in the blood during intense exercise.
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Anaerobic exercise
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Exam-style questions
1. Describe the passage of oxygen from the nasal passages
to the bloodstream.
2. David goes jogging once a week for 45 minutes
David tries to increase his pace. He finds that he is forced
to stop running and breathe hard for several minutes.
c) Explain why David had to stop.
d) How did breathing hard help him to recover?
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Can you remember all these keywords?
Larynx
Minute volume
Trachea
Vital capacity
Bronchus / Bronchi
Residual volume
Bronchioles
Aerobic respiration
Alveoli
Anaerobic respiration
Diaphragm
Oxygen debt
Intercostal muscles
Lactic acid
Oxygen uptake
Tidal volume
Respiratory rate
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