Human Respiratory System

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Human Respiratory System

• As all living cells carry out respiration to
  release energy in order to maintain life, oxygen
  is needed and waste carbon dioxide (toxic at high
  levels) produced has to be gotten rid of
  continuously
• Hence, all organisms have to exchange gases with
  the surroundings
• This process is called gas exchange

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Gas Exchange in Simple Animals
In small organisms, in which the surface
area-to-volume ratio is large (e.g. Amoeba and
earthworm), gas exchange occurs by simple
diffusion across the cell surface
O2
CO2
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Gas Exchange in Higher Order Animals

• Larger organisms use specialized respiratory
  surfaces with a large surface area-to-volume
  ratio for gas exchange as simple diffusion is not
  efficient enough
• e.g. fish use gills
• frogs use skin, mouth and lungs
• mammals (including humans) use lungs

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Breathing

• Breathing involves two processes
• VENTILATION
• GAS EXCHANGE

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Ventilation vs. Gas Exchange

• Ventilation is the process of breathing in and
  breathing out of air
• Inhalation/Inspiration breathing in
• Exhalation/Expiration breathing out
• Gas exchange is the exchange of gases between the
  lungs and the blood

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Human Respiratory System
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Human Respiratory System
lungs
rib
thoracic cavity
heart
diaphragm
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Human Torso Model

• Can you identify all the parts that are involved
  in breathing (i.e. the breathing system) in the
  human torso model?

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Nostrils and Nasal Cavity

• Nostrils openings on the nose
• Nasal cavity the area inside the nose
• The nasal cavity and mouth cavity are separated
  by the palate, allowing a person to breathe and
  chew food at the same time

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Nostrils and Nasal Cavity

• Air enters the nasal cavity through the two
  nostrils
• Inside the nasal cavity is hair for trapping
  large dust particles
• The wall of the nasal cavity is lined with
  ciliated epithelium (cilia) and mucus-secreting
  cells

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Nostrils and Nasal Cavity

• The mucus will moisten the incoming air
• The mucus will also trap bacteria and dust
• the beating cilia will move trapped particles
  towards the throat to be coughed out or swallowed
• The nasal cavity also contains sensory cells to
  detect chemicals in air (sensation of smell)

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Nostrils and Nasal Cavity

• There are numerous blood vessels lying close to
  the surface of the nasal cavity
• The blood vessels bring heat and help to warm up
  the incoming air to reach body temperature
• Therefore, air is warmed, moistened and filtered
  before entering the lungs

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Nostrils and Nasal Cavity
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Pharynx and Larynx

• Air passes from the nasal cavity to the pharynx
  (a common passage for food and air)
• Air then enters the larynx, which is the
  beginning part of the trachea
• The larynx is consisted of cartilages
• The opening to the larynx is the glottis
• During swallowing, the epiglottis covers the
  glottis to prevent food from entering the trachea

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Vocal Cords

• Inside the voice box (larynx) are two membranes
  called the vocal cords
• When we talk, muscles contract to stretch the
  vocal cords and create tension. The gap between
  the cords becomes narrower, leaving a very thin
  opening. As we talk, we exhale air and this
  stream of air passes through the narrow passage,
  causing the vocal cords to vibrate and produce
  sound
• Tension of the vocal cords determine the pitch of
  voice

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Damage to Vocal Cords

• Screaming or making excessive loud noises can
  damage the vocal cords, hardening them or leading
  to formation of nodules or webs that make the
  voice coarse

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Trachea (Windpipe)

• Air enters into the trachea (lying in front of
  the oesophagus) through the glottis
• The trachea is lined with ciliated epithelium and
  mucus-secreting cells to prevent entry of
  bacteria and dust
• The trachea is strengthened by C-shaped
  cartilages which support the trachea and prevent
  it from collapsing during inhalation and
  swallowing

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Bronchi

• The trachea divides into two tubes called the
  bronchi (singular bronchus)
• Left bronchus -gt left lungs
• Right bronchus -gt right lungs

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Bronchioles

• Each bronchus subdivides into many small tubes
  called the bronchioles

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Air Sacs/Alveoli

• The bronchioles end up in numerous tiny
  balloon-like air sacs called alveoli (singular
  alveolus)
• The alveoli provide the respiratory surface where
  oxygen is taken into blood and carbon dioxide is
  released into the lungs by diffusion
• There are numerous (300 million) alveoli to
  provide a large surface area (140 m2 , size of a
  singles tennis court) for diffusion of gases

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Air Sacs/Alveoli

• The inner surface of alveoli is covered by a
  fluid for oxygen to dissolve in before diffusing
  across wall of alveolus into blood
• Wall of each alveolus is only one-cell thick to
  provide a short distance for diffusion of gases
• The alveoli are surrounded by numerous
  capillaries (blood vessels) to provide a rich
  blood supply to transport gases rapidly to
  maintain a steep diffusion gradient of gases

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Lungs

• Located in the thorax (thoracic cavity)
• Pink in colour (contains many blood capillaries)
• Spongy (contains air sacs)
• Protected by rib-cage (vertebral column at the
  back, ribs with intercostal muscles along the
  sides and sternum at the front)
• The diaphragm separates the thoracic cavity from
  the abdomen

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Lungs

• Each lung is surrounded by pleural membranes
• Outside of lungs linked to inner pleural
  membrane
• Inner surface of rib cage and diaphragm linked
  to outer pleural membrane
• Pleural cavity air tight space between the
  pleural membranes
• Pleural fluid fluid inside the pleural cavity
  that is secreted by pleural membranes. The
  fluid acts as a lubricate and can help to reduce
  the friction caused by the rubbing between the
  lungs and ribcage

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Investigation 1 Comparing
the oxygen levels in inhaled and exhaled air
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Purpose of Investigation

• In this experiment, we are going to compare the
  amount of oxygen in inhaled and exhaled air (i.e.
  does inhaled or exhaled air contain more oxygen?)
• Since burning requires oxygen, we are going to
  use a burning candle to determine the amount of
  oxygen present in inhaled and exhaled air

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How to collect exhaled air

• Fill a small gas jar with water and invert it
  over a trough of water
• Breathe air through a rubber tubing into the gas
  jar until no water is present in the jar
• Use a glass plate to cover the opening of the jar
  and stand it upright

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Procedure
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Procedure
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Investigation 2 Comparing
the carbon dioxide levels in inhaled and exhaled
air
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Purpose of Investigation

• In this experiment, we are going to compare the
  amount of carbon dioxide in inhaled and exhaled
  air (i.e. does inhaled or exhaled air contain
  more carbon dioxide?)
• Hydrogencarbonate indicator solution/ lime
  water can be used to test for carbon dioxide (it
  will change from orange-red to yellow in
  colour/it will change from clear to milky and
  cloudy)

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Procedure
To mouth
Clip Y
Clip X
boiling tubes
lime water
Open Clip X Breathe in Open Clip Y Breathe
out
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Gas Atmospheric Air/ Inhaled Air () Exhaled Air ()
Oxygen 21 16 (5 used by cells)
Carbon Dioxide 0.03 4 (4 produced by cells)
Nitrogen 78 78 (N2 is not used/produced by cells)
Other Gases 1 1
Water Vapour Variable Saturated (from lungs surfaces)
Temperature Variable 37oC (air warmed by body)
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Gas Exchange

• Gases are exchanged through the gas exchange
  surface
• In humans, the gas exchange surface is the air
  sacs/alveoli in the lungs
• Gases are exchanged between the air in the air
  sacs and the blood in the blood capillaries

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Red blood cell with haemoglobin
Capillary wall (one-cell thick)
Plasma (liquid part of blood)
Mucus (film of moisture)
Alveolar wall (one-cell thick)
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Gas Exchange

• Oxygen gas breathed in through the nostrils
  entering the alveoli will diffuse from the
  inhaled air to the residual air inside the
  alveoli
• It will dissolve in the film of moisture (mucus)
  lining the inner wall of each alveolus

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Gas Exchange

• Dissolved oxygen then diffuses down the
  concentration gradient across alveolar wall and
  capillary wall into blood capillary (higher
  concentration of oxygen in air than in blood)
• It combines with haemoglobin in the red blood
  cells to form oxyhaemoglobin

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Haemoglobin protein molecule in RBC used to
carry oxygen
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Gas Exchange

• Blood now becomes oxygenated and bright red (with
  high oxygen content and low concentration of
  carbon dioxide)
• Oxygen is carried by blood as oxyhaemoglobin from
  the lungs to the heart and the rest of the body
  through the pulmonary veins

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Gas Exchange

• On reaching tissue cells, oxyhaemoglobin is
  changed back into haemoglobin by releasing oxygen
  to the cells for respiration. Carbon dioxide
  produced by the tissue cells is carried by the
  plasma in the form of hydrogencarbonate (HCO3-)
  ions back to the alveoli through the pulmonary
  artery (some carbon dioxide can be carried by
  haemoglobin also)

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Gas Exchange

• Dull red deoxygenated blood (with low
  concentration of oxygen and high concentration of
  carbon dioxide) is carried to the lungs by the
  pulmonary artery from the heart
• The artery branches into numerous capillaries on
  the surface of the alveoli

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Gas Exchange

• At the lungs, HCO3- converts back into CO2 and
  diffuses down the concentration gradient across
  the capillary wall and alveolar wall into the
  alveoli (concentration of carbon dioxide is
  higher in blood than in air in lungs)
• Carbon dioxide then leaves the alveoli and is
  breathed out of the lungs
• Exhaled air also contains water vapour as the
  moisture inside alveoli evaporates during
  exhalation

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Exhaled air (4 CO2 16 O2)
Inhaled air (21 O2 0.03 CO2)
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Adaptation Reason
Thin walls (one-cell thick)
Large number of air sacs present
Water film covering the air sacs
Dense network of blood capillaries around air sacs
Shorter distance for gases to diffuse
Large surface area for gas exchange to occur
Oxygen can dissolve in water for diffusion to
occur
Allow rapid transport of gases
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Artificial Respiration

• Any measure that causes air to flow in and out of
  a person's lungs when natural breathing is
  inadequate or ceases
• Mouth-to-mouth or mouth-to-nose resuscitation
• Oxygen in exhaled air maintains aerobic
  respiration
• Carbon dioxide in exhaled air stimulates
  breathing centre in brain
• If there is no pulse either, then cardiopulmonary
  resuscitation is needed

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Cardiopulmonary Resuscitation

• Check the victim to see if he/she responds
• If not, call for help and follow the steps below
• Turn the victim on to his/her back
• Access the ABCs (Airway, Breathing and
  Circulation) make sure the victims heart and
  lungs are working

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Cardiopulmonary Resuscitation

• Airway - open the mouth and check for false
  teeth, vomit or food debris. Use a finger to
  sweep the airway clear, and tilt the victims
  chin upwards

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Cardiopulmonary Resuscitation

• Breathing - check to see if the chest is moving
  and also feel for breath. If the person is not
  breathing after 10 seconds start artificial
  respiration (mouth-to-mouth)

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Cardiopulmonary Resuscitation

• Circulation - if there is no movement or coughing
  assume the heart has stopped and start
  cardiopulmonary resuscitation (CPR)

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Cardiopulmonary Resuscitation

• Tilt the head and lift the chin
• Observe for breathing and signs of life for 10
  seconds. If victim is not breathing give 2
  breaths of artificial ventilation whilst holding
  the nose closed
• Push down on the chest 1.5 to 2 inches 15 times. 
  Pump at the rate of 100/minute, faster than once
  per second.
• Give 2 more ventilations then give a further 15
  compressions
• Repeat the cycle until help arrives

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Cardiopulmonary Resuscitation
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Breathing Mechanism

• Movement of air over the respiratory surface is
  called ventilation and is achieved by the action
  of breathing
• Breathing is brought about by the action of the
  diaphragm and the intercostal muscles

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Inspiration /Inhalation

• The diaphragm muscles contract and the diaphragm
  is flattened
• The intercostal muscles contract and the rib cage
  is raised
• The volume of the thoracic cavity increases
• Pressure inside the lungs becomes lower than the
  atmospheric pressure
• Air rushes into the lungs through the trachea

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Inspiration /Inhalation
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Expiration/Exhalation

• The diaphragm muscles relax and the diaphragm
  returns to dome-shape
• The intercostal muscles relax and the rib cage is
  lowered
• The volume of the thoracic cavity is reduced
• Pressure inside the thoracic cavity increases and
  is higher than the atmospheric pressure
• Air is forced out of the lungs

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Expiration/Exhalation
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Bell Jar Model

• The action of the diaphragm in breathing can be
  demonstrated by the bell jar model. How???

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Feature in the model Corresponding structure in the breathing system
Y-shaped tube
Balloons
Wall of bell jar
Cavity in bell jar
Rubber sheet
Trachea and bronchus
Lungs
Thoracic wall
Pleural cavity
Diaphragm
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Rubber sheet pulled down Rubber sheet released
Volume inside bell jar
Pressure inside bell jar
Comparison with atmospheric pressure
Direction of air movement
Shape of balloons
Increased
Decreased
Decreased
Increased
Lower than atmospheric pressure
Higher than atmospheric pressure
Drawn into the balloons
Forced out from the balloons
Inflated
Deflated
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Condition in the bell jar model Actual condition in the human body
Shape of diaphragm during exhalation
Shape of diaphragm during inhalation
Movement of thoracic cage in breathing
Content of pleural cavity
Any other differences
The rubber sheet is flattened
The diaphragm is dome-shaped
The rubber sheet is pulled down
The diaphragm is flattened
The thoracic wall is flexible and can change
shape
The wall of the jar is rigid
The cavity of the jar is filled with air
The pleural cavity is filled with pleural fluid
Controlled by hands
Controlled by muscles
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Rib Cage Model

• The action of the intercostal muscles in
  breathing can be demonstrated by the rib cage
  model. How???

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Feature in the model Corresponding structure in the breathing system
Rod P
Rod Q
Rod R
Elastic band
Backbone
Sternum
Rib
Intercostal muscle
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Rib cage in the human body Rib cage model
Inhalation
Inhalation
Exhalation
Exhalation
Contraction of intercostal muscles
Shortening of the elastic band
Upward and outward movement of rib cage
Upward and outward position of rods R and Q
Lengthening of the elastic band
Relaxation of intercostal muscles
Downward and inward movement of rib cage
Downward and inward position of rods R and Q
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Condition in the rib cage model Actual condition in the human body
Dimension
Number of ribs
Contraction and relaxation of intercostal muscles
Any other differences
Model is 2-D structure
Thoracic cavity is 3-D structure
Only two rods are shown
12 pairs of ribs
Controlled by the moving rods
Intercostal muscles contract and relax by
themselves
Few intercostal muscles are shown
Many intercostal muscles are present
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Breathing Mechanism

• Exhalation

• Inhalation

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Changes in Pressure in Lungs
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Inspiration Expiration
1. Diaphragm muscles
2. Diaphragm
3. Intercostal muscles
4. Ribs and sternum
5. Volume of thoracic cavity
6. Pressure inside cavity
7. Movement of air
8. Shape of lungs
Contract
Relax
Flattens
Dome shape
Contract
Relax
Raised
Lowered
Increases
Decreases
Decreases
Increases
Rushes into lungs
Forced out of lungs
Inflated
Deflated
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Coughing and Hiccupping

• A cough is a sudden, explosive movement of air
  that tends to clear materials from the airways.
  It is a complicated reflex
• Hiccup is the result of sudden contraction of the
  diaphragm often caused by drinking or eating too
  fast

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Coughing

• As you breathe in, the glottis opens to allow air
  into your lungs

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Coughing

• The glottis then closes, trapping the air inside
  your lungs

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Coughing

• The glottis suddenly opens and air from your
  lungs rushes out of your mouth, clearing the
  irritation

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Hiccupping

• 1. The glottis is open and the diaphragm is
  relaxed

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Hiccupping

• 2. The diaphragm contracts causing a sudden deep
  inhalation of air into your lungs

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Hiccupping

• 3. As air rushes into the lungs, the glottis
  snaps shut with a distinctive click

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Lungs Diseases

• Asthma
• Bronchitis
• Cystic fibrosis
• Emphysema
• Pneumonia
• Pneumothorax
• Lung cancer

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Rate of Breathing

• How fast a person is breathing
• Expressed in terms of the number of breaths in a
  minute
• When a person is at rest, the rate of breathing
  is about 15 times per minute and only diaphragm
  movement is involved
• When a person is active, breathing also involves
  both the diaphragm and the intercostal muscles

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Breathing Rate Before and After Exercise
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Breathing Rate Before and After Exercise
1. What is the effect of exercise on the rate of
breathing?
The rate of breathing increases
2. Is there any other change in breathing after
exercise?
The depth of breathing increases
3. What is the significance of these changes?
These changes provide the muscles with more
oxygen for increased rate of respiration to
release more energy for muscle contraction
These changes also help the body to remove the
additional amount of carbon dioxide produced by
respiration
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Breathing Rate Before and After Exercise
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Depth of Breathing

• How deep a person is breathing
• The volume of air breathed in after an exhalation
• The depth of breathing at rest is about 0.5 litre
  
• Can be measured using a spirometer

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Effect of Exercise on Rate and Depth of Breathing

• Exercise can increase the number of capillaries
  in the lungs, increase the size of alveoli and
  strengthen the intercostal muscles and diaphragm
  muscles
• Regular exercise makes a person more fit. The
  person can breathe deeper with each breath during
  exercise and his/her breathing rate does not
  increase as much as an unfit person

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Changes in Lung Volume Before and After Exercise
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Changes in Lung Volume Before and After Exercise
Rate of breathing 6 x (60/20) 18 breaths per
minute
Depth of breathing 2500 - 2000 500 cm3
Volume of air breathed in per minute 18 X 500
9000 cm3
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Changes in Lung Volume Before and After Exercise
Rate of breathing 9 x (60/20) 27 breaths per
minute
Depth of breathing 3500 - 1500 2000 cm3
Volume of air breathed in per minute 27 x 2000
54000 cm3
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Changes in Lung Volume Before and After Exercise
The volume of oxygen retained in the body per
minute At rest 18 x 500 x (21 - 16) 450
cm3 During exercise 27 x 2000x (21 - 16) 2700
cm3 The volume of carbon dioxide produced by the
body per minute At rest 18 x 500 x (4 -
0.03) 357.3 cm3 During exercise 27 x
2000 x (4 - 0.03) 2143.8 cm3
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Volumes of Air
Tidal volume increases during exercise while
vital capacity remains unchanged
Vital capacity can only be increased by prolonged
training
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Volumes of Air

• Tidal volume during quiet breathing, the volume
  of air moved into and out of the lungs (0.5
  litre)

• Tidal air air that can be breathed in and out
  the lungs in each breath

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Volumes of Air

• Vital Capacity the maximum volume of air that
  can be forced out of the lungs after the deepest
  inspiration (3-5 litres)

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Volumes of Air

• Residual volume volume of air left inside the
  lungs after the greatest expiration (1.5 litres)

• Residual air the air that cannot be exchanged
  with the atmosphere

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Volumes of Air

• Total lung capacity total amount of air that
  can be present inside the lungs (4-7 litres)

• Total lung capacity Vital capacity Residual
  Volume

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Estimation of Vital Capacity of the Lungs
Air breathed out
Plastic bottle
Rubber tubing
Water trough
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Spirometer
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Control of Breathing

• An increase in the concentration of carbon
  dioxide in blood will cause an immediate increase
  in the rate and depth of breathing
• A decrease in the concentration of oxygen in
  blood can also cause an increase in the rate and
  depth of breathing (e.g. at high altitudes)
• Breathing is automatically controlled by the
  breathing centres in the medulla oblongata of the
  brain

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Smoking and Health Hazards

• Tobacco smoke contains over 4,000 different
  chemicals. At least 43 are known carcinogens
  (cause cancer in humans)
• The smoke can irritate the bronchi to become
  narrowed
• Heat can damage the alveoli

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Smoking and Health Hazards

• 1) Tar
• Carcinogenic
• Increases the secretion of mucus and stops the
  action of cilia
• As a result, tar and dirt particles will cover
  the alveoli
• Smoker will cough a lot and produce a lot of
  phlegm
• Can lead to infection, chronic bronchitis and
  emphysema
• Tar can stain teeth, nail, etc.

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Smoking and Health Hazards

• Breakdown of alveoli wall can reduces surface
  area for gaseous exchange
• This leads to emphysema

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Smoking and Health Hazards

• 2) Carbon monoxide
• Combines more readily with haemoglobin and as a
  result reduce the oxygen-carrying capacity of
  blood
• Can lead to heart disease

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Smoking and Health Hazards

• 3) Nicotine
• Causes dependency
• Increases heart rate and blood pressure
• Causes the build-up of fats along the arterial
  walls, leading to heart disease
• Retards growth of foetus
• Stimulate the brain

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Lung Cancer
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Smoking and Health Hazards
Conclusion The more cigarettes a person smokes
per day, the greater the chance of dying from
lung cancer.
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Smoking and Health Hazards
Conclusions The risk of getting lung cancer is
greatly reduced after quitting Non-smokers may
also die from lung cancer though the risk is very
low (passive smoking)
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Smoking and Health Hazards
Conclusion Cigarettes smoking is more hazardous
to health than other types of tobacco smoking
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Smoking and Health Hazards
Conclusions The higher the age, the greater the
risk of dying from coronary disease The more
cigarettes smoked daily, the greater the risk of
dying from coronary heart disease
Relationship between no. of cigarettes smoked
daily and the annual death rate from coronary
heart disease
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The Smoking Machine