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THE RESPIRATORY SYSTEM
A guide to respiratory fitness
© Copyright Ali Clarke Design 2003
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Contents - Respiratory
Introduction
Structure of the respiratory system
Breathing
Lung function
Lung capacity
Summary
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Introduction


what is the respiratory system
function of the respiratory system
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What is the respiratory system?
The respiratory system is made up from the
following components;
 Lungs
 Airways
 Blood supply
 Respiratory muscles
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Function of the respiratory system
 To get air into the body so oxygen can be added
to the blood
 To remove the waste gas carbon dioxide from
the body
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The respiratory system
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Structure of the Respiratory System
 upper airways
 lower airways
 structure of the airways
 lungs
 blood vessels
 respiratory muscles
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Structure of the respiratory system
 The respiratory system is made up from several
components
Airways
– allow oxygen into the body
Lungs
– deliver oxygen to the bloodstream
Blood vessels – deliver oxygen to the body tissues
Respiratory
muscles
– move air in/out of the airways & lungs
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The upper airways
 The airways are divided into upper & lower
 The upper airways begin in the nose/throat region, or
nasopharynx
 Inhaled air travels down through the ‘voice-box’ (or larynx)
before entering the ‘windpipe’, also called the trachea
 The trachea then divides into the right & left main
bronchus, supplying air to each lung
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The lower airways
 Each main bronchus splits into increasingly smaller branches,
called bronchioles, that reach every part of the lung tissue
 The bronchioles finally divide into tiny sacs, called alveoli,
where the exchange of oxygen (O2) for waste carbon dioxide
(CO2) in the blood takes place
 There are more than 300 million alveoli in each lung, providing
a huge total surface area for oxygenation to take place
(equivalent the to area of a tennis court!)
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Structure of the airways
nasal cavity
nasopharynx
epiglottis
larynx
trachea
oesophagus
Upper airways
Lower airways
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The lungs
 The lungs are the organs that allow us to breathe
 Each lung is joined to a main bronchus, which is then
attached to the trachea (windpipe)
 The lungs are surrounded by a thin membrane called
the pleura
 Each lung is divided into regions called lobes
 The lungs have a soft, spongy texture that allows them to
stretch as we take a breath
 The inside of the lung contains numerous airways that divide
many times to resemble the branches of a tree
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Structure of a lung
Windpipe (Trachea)
Bronchus
Lung tissue
Bronchiole
Alveolar
sacs
Pleural
membrane
Lungs
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Blood vessels
 Lung tissue has a very rich blood supply
 This allows as much blood as possible to pass through
the alveoli (air sacs) for oxygenation
 The oxygenated blood travels to the heart to be pumped
to the body tissues
 Deoxygenated blood containing waste CO2 travels to the
heart & is then pumped back to the lungs for more O2 to
be added (& so on…)
 This movement of blood between the heart & lungs is
called the pulmonary circulation
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Blood vessels
Lung Capillaries
Pulmonary
Artery
Pulmonary
Vein
To
Body
From
Body
Right heart
Left heart
Pulmonary circulation
Blood vessels
in the lung
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Respiratory muscles
 Various muscles are required to contract &
relax in order to move air in & out of the lungs
 These are called the ‘respiratory muscles’ and
include the
Intercostal Muscles
Diaphragm
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Respiratory muscles
 Intercostal muscles
 Lie between the ribs
 They contract to pull the ribs up & out, opening up the chest
& expanding the lungs
 Diaphragm
 A large, dome-shaped muscle that divides the chest from the
abdomen
 The base of each lung is attached to it
 It contracts & flattens, pulling the lungs down to expand them
& opening the chest
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Respiratory muscles
Nasopharynx
Larynx
Trachea
Sternum
Lung
Diaphragm
Intercostals (shaded)
Intercostal muscles
Diaphragm
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Breathing
 how oxygen gets in
 how carbon dioxide is removed
 mechanisms for breathing
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How does oxygen get in?
 The air we breathe passes through the upper airways
first; nasopharynx, larynx, trachea & main bronchi
 It then enters the lower airways of the lungs; small
bronchi & bronchioles
 Finally, the air enters the many tiny air sacs, or alveoli
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How does oxygen get to the tissues?
 The alveoli are covered with microscopic, thin-walled
blood vessels, called capillaries
 O2 from the air is taken up into the blood within these
capillaries, it then flows into the larger blood vessels &
eventually ends up in the heart
 Oxygenated blood is pumped out of the heart & into
the blood vessels supplying the body’s tissues
 Upon reaching the tissues, the O2 is released & the
blood is said to be deoxygenated
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How is carbon dioxide removed?
 Waste CO2 produced by the cells is collected in the
blood & travels back to the heart via the circulation
 This deoxygenated blood is pumped from the heart into
the blood vessels of the lung, eventually arriving in the
capillaries
 The capillaries lining the alveoli release CO2 into the air
sacs, it then travels up the airways & out of the body
into the atmosphere
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How do we breathe in?
 To move air into the lungs, the volume of the chest must be
made to increase by contracting the respiratory muscles;
Intercostals – pull ribs up & out
Diaphragm – flattens downward, stretching lungs
 This increase in chest volume makes the pressure inside
the body lower than that outside the body
 This causes air to be sucked down the airways
& into the lungs
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Mechanism of breathing in
inspiration
contracting
Diaphragm
(Inspiration)
Intercostals
(Inspiration)
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How do we breathe out?
 Moving air out of the lungs involves reducing chest
volume by relaxing the respiratory muscles;
Intercostals – ribs move in & down
Diaphragm – pushes upwards
 This decrease in chest volume makes the pressure
inside the body higher than that outside
 This causes air to be squeezed out of the lungs & up
into the airways
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Mechanism of breathing out
expiration
relaxing
Diaphragm
(Expiration)
Intercostals
(Expiration)
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Lung Function
 gaseous exchange
 respiration
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Gaseous exchange: O2
 This is the addition of oxygen to the blood & the removal of
waste carbon dioxide from it; i.e. it is the ‘exchange’ of one
gas (CO2) for another (O2)
 Gaseous exchange takes place in the air sacs of the lung,
called the alveoli
 The lining of each alveolus is very thin & is covered by a
network of tiny blood vessels, called capillaries
 O2 from inhaled air travels across the alveolar lining & enters
the capillaries
 Here, it is taken up by red blood cells in a special oxygencarrying molecule called haemoglobin
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Gaseous exchange: CO2
 Waste CO2 must also be removed from the body
 CO2 is released from the cells & taken up by the tissue
capillaries, where it dissolves into the blood
 CO2 is then carried in the blood vessels until it eventually
reaches the capillaries that line the lung alveoli
 CO2 travels out of the capillaries & across the alveolar
lining to enter the ‘airway tree’
 CO2 is then pushed out of the body during expiration
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Cellular respiration
 This is the process whereby cells breakdown O2 &
nutrient (sugar) to release energy
 CO2 is formed as a waste product during this process
 Respiration can be expressed in this simplified equation:
O2 + sugar 
(oxygen)
energy
+ CO2 + H20
(carbon
dioxide)
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(water)
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Lung Capacity
 lung capacity
 lung capacity & fitness
 effects of exercise
 effects of smoking
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Lung capacity
 The amount of air breathed in/out during normal
breathing is called the tidal volume
 The largest amount of air that can be forced out of the
lungs after taking as big a breath in as possible is called
the vital capacity
 The amount of air left behind is called the
residual volume
 Lung function is measured using a peak flow meter or a
more complex machine called a spirometer
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Lung capacity
normal breaths
maximum exhalation
Tidal
volume
Vital
capacity
Total
lung
capacity
Residual
volume
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Lung capacity & fitness
 Lung capacity varies with age, sex, body shape, &
level of fitness
 ‘Lung capacity’ is not the same as ‘respiratory fitness’
 Respiratory fitness is determined by measuring the
maximum amount of O2 that can be used by a
person’s body, this is called VO2max
 The higher VO2max the fitter the individual
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Effect of exercise
 The respiratory system responds to the demands of
exercise
 More O2 is required by the muscles & more CO2 is
produced for removal
 Breathing rate increases
 Depth of breathing increases (maximum = vital capacity)
 Blood flow through lungs increases
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Exercise
 Exercise keeps the lungs in good condition
 Gives your heart & lungs a good workout
 Promotes a healthy lifestyle
 Improves your quality of life
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Effect of smoking
 Smoking damages your lungs
 Reduces the amount of O2 that
can be carried in the blood
 Damages the lining of the airways &
increases the amount of mucus produced
 Reduces alveolar function
 Increases the risk of lung infection, emphysema,
bronchitis, asthma, & lung cancer
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Smoking & fitness
 Smoking damages your fitness
 Reduces lung vital capacity
 Reduces aerobic fitness
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Respiratory system: summary
 Respiratory system =
lungs + airways + blood supply + muscles
 Adds O2 to blood & removes CO2 from it
 Exercise improves respiratory fitness
 Exercise keeps the respiratory system healthy
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