Respiratory System

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
Gas Exchange in Simple Animals
In small organisms, in
which the surface areaO2 to-volume ratio is large
(e.g. Amoeba and
earthworm), gas
exchange occurs by
simple diffusion across
the cell surface
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
Breathing involves
two processes:
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
Human Respiratory System
Human Respiratory System
Human Torso Model
• Can you identify all
the parts that are
involved in breathing
(i.e. the breathing
system) in the human
torso model?
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
Nostrils and Nasal Cavity
• Air enters the nasal cavity through the two
• Inside the nasal cavity is hair for trapping
large dust particles
• The wall of the nasal cavity is lined with
ciliated epithelium (cilia) and mucussecreting cells
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
• The nasal cavity also contains sensory cells
to detect chemicals in air (sensation of smell)
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
Nostrils and Nasal Cavity
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
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
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
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
• The trachea
divides into two
tubes called the
bronchi (singular:
• Left bronchus ->
left lungs
• Right bronchus ->
right lungs
• Each bronchus
subdivides into
many small tubes
called the
Air Sacs/Alveoli
• The bronchioles end up in numerous tiny
balloon-like air sacs called alveoli (singular:
• 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
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
• Located in the thorax (thoracic cavity)
• Pink in colour (contains many blood
• 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
• 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
• 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
Investigation #1:
Comparing the oxygen levels in
inhaled and exhaled air
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
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
Investigation #2:
Comparing the carbon dioxide
levels in inhaled and exhaled air
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)
To mouth
Clip Y
Clip X
Open Clip X – Breathe in; Open Clip Y – Breathe out
Atmospheric Air/
Inhaled Air (%)
Exhaled Air (%)
16% (~5% used by
Carbon Dioxide
4% (~4% produced by
Other Gases
78% (N2 is not
used/produced by
Water Vapour
Saturated (from lungs
~37oC (air warmed by
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
Red blood cell with
Capillary wall
(one-cell thick)
Plasma (liquid
part of blood)
Mucus (film of
Alveolar wall (one-cell thick)
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
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
Haemoglobin – protein molecule in RBC used to carry oxygen
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
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)
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
• The artery branches into numerous
capillaries on the surface of the alveoli
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
Inhaled air (21% O2 & 0.03% CO2) Exhaled air (4% CO2 & 16% O2)
Thin walls (one-cell thick)
Shorter distance for gases
to diffuse
Large number of air sacs
Large surface area for gas
exchange to occur
Water film covering the air Oxygen can dissolve in
water for diffusion to occur
Allow rapid transport of
Dense network of blood
capillaries around air sacs gases
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
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 ABC’s (Airway, Breathing and
Circulation) – make sure the victim’s heart
and lungs are working
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 victim’s chin
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-tomouth)
Cardiopulmonary Resuscitation
• Circulation - if there is
no movement or
coughing assume the
heart has stopped and
start cardiopulmonary
resuscitation (CPR)
Cardiopulmonary Resuscitation
1. Tilt the head and lift the chin
2. 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
3. Push down on the chest 1.5 to 2 inches 15
times. Pump at the rate of 100/minute, faster than
once per second.
4. Give 2 more ventilations then give a further 15
5. Repeat the cycle until help arrives
Cardiopulmonary Resuscitation
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
Inspiration /Inhalation
The diaphragm muscles
contract and the diaphragm is
The intercostal muscles
contract and the rib cage is
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
Inspiration /Inhalation
The diaphragm muscles relax
and the diaphragm returns to
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
Bell Jar Model
• The action of
the diaphragm
in breathing
can be
by the bell jar
model. How???
Feature in the model
Corresponding structure in
the breathing system
Y-shaped tube
Trachea and bronchus
Wall of bell jar
Thoracic wall
Cavity in bell jar
Pleural cavity
Rubber sheet
Rubber sheet
pulled down
Rubber sheet
Volume inside
bell jar
Pressure inside
bell jar
Comparison with
Lower than
Drawn into the
Higher than
Forced out from
the balloons
Direction of air
Shape of balloons Inflated
Condition in the bell Actual condition in
jar model
the human body
Shape of diaphragm
during exhalation
The rubber sheet is
The diaphragm is
Shape of diaphragm
during inhalation
The rubber sheet is
pulled down
The diaphragm is
The cavity of the jar
is filled with air
The thoracic wall is
flexible and can
change shape
The pleural cavity is
filled with pleural fluid
Any other differences Controlled by hands
Controlled by muscles
Movement of thoracic The wall of the jar is
cage in breathing
Content of pleural
Rib Cage Model
• The action of the
intercostal muscles in
breathing can be
demonstrated by the rib
cage model. How???
Feature in the model
Corresponding structure
in the breathing system
Rod P
Rod Q
Rod R
Elastic band
Intercostal muscle
Rib cage in the
human body
Rib cage model
Contraction of
intercostal muscles
Shortening of the
elastic band
Upward and outward Upward and outward
movement of rib cage position of rods R and Q
Relaxation of
intercostal muscles
Lengthening of the
elastic band
Downward and inward Downward and inward
movement of rib cage position of rods R and Q
Condition in the rib
cage model
Actual condition in
the human body
Model is 2-D
Thoracic cavity is
3-D structure
Number of ribs
Only two rods are
12 pairs of ribs
Contraction and
Controlled by the
relaxation of
moving rods
intercostal muscles
Intercostal muscles
contract and relax
by themselves
Any other
Many intercostal
muscles are present
Few intercostal
muscles are shown
Breathing Mechanism
• Inhalation
• Exhalation
Changes in Pressure in Lungs
1. Diaphragm muscles
2. Diaphragm
Dome shape
3. Intercostal muscles
4. Ribs and sternum
5. Volume of thoracic
6. Pressure inside cavity
7. Movement of air
Rushes into lungs Forced out of lungs
8. Shape of lungs
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
1. As you breathe in, the
glottis opens to allow
air into your lungs
2. The glottis then
closes, trapping the
air inside your
3. The glottis
suddenly opens
and air from your
lungs rushes out of
your mouth,
clearing the
1. The glottis is open
and the diaphragm
is relaxed
2. The diaphragm
contracts causing a
sudden deep
inhalation of air into
your lungs
3. As air rushes into
the lungs, the glottis
snaps shut with a
distinctive click
Lungs Diseases
Cystic fibrosis
Lung cancer
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
Breathing Rate Before and After Exercise
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
Breathing Rate Before and After Exercise
Depth of Breathing
• How “deep” a person is breathing
• The volume of air breathed in after an
• The depth of breathing at rest is about 0.5 litre
• Can be measured using a spirometer
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
Changes in Lung Volume Before and After Exercise
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
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
27 x 2000 = 54000 cm3
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
Volumes of Air
Tidal volume increases during exercise while vital capacity remains
unchanged Vital capacity can only be increased by prolonged training
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
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)
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
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
Estimation of Vital Capacity of the Lungs
Air breathed out
Plastic bottle
Rubber tubing
Water trough
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
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
• Heat can damage the
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
• Smoker will cough a lot and produce a lot of phlegm
• Can lead to infection, chronic bronchitis and
• Tar can stain teeth, nail, etc.
Smoking and Health Hazards
• Breakdown of alveoli
wall can reduces
surface area for
gaseous exchange
• This leads to
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
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
Lung Cancer
Smoking and Health Hazards
The more cigarettes a
person smokes per
day, the greater the
chance of dying from
lung cancer.
Smoking and Health Hazards
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)
Smoking and Health Hazards
Cigarettes smoking is
more hazardous to
health than other types
of tobacco smoking
Smoking and Health Hazards
The higher the age,
the greater the risk
of dying from
coronary disease
Relationship between no. of cigarettes
smoked daily and the annual death rate
from coronary heart disease
The more cigarettes
smoked daily, the
greater the risk of
dying from coronary
heart disease
The Smoking Machine