2. The Human Breathing Mechanism
•The human respiratory system provides an area for gas
exchange between the blood and the environment. It
allows oxygen acquisition and the carbon dioxide
elimination.
•The gas exchange in lungs is called breathing (external
respiration). This exchange involves the taking in and
letting out of air.

3. Structure of Human Respiratory System
•Air enters the respiratory system through the nasal
cavity.
•As air passes the nasal cavity, it is warmed and
moistened. Dust is trapped by the hairs.
•After the air leaves the nasal cavity, it enters the
trachea.
•The wall of the trachea contains C – shaped rings
of cartilage which give it support and prevent it
from collapsing during inhalation.
•The trachea branches into two bronchi (singular:
bronchus)

4. •One bronchus enters the right lung, the others enters the
left lung.
•Each bronchus branches into smaller tubes called
bronchioles.
•The bronchioles end in millions of tiny air sacs called
alveoli (singular: alveolus).
• the lungs are made up of alveoli, bronchioles and blood
capillaries.
•The lungs are located in a space called the thoracic cavity.
•The lungs are protected by the ribcage which consists of
ribs and intercostal muscles.
•The sheet of muscle called the diaphragm separates the
thoracic cavity from the abdomen.

5. The human respiratory system

6. Adaptation of the alveoli for efficient gas exchange
•Large surface area – the lungs have millions of alveoli to
provide a large surface area for gas exchange.
•Very thin walls – the wall of each alveolus is one cell –
thick to provide a very short distance for the diffusion of
gases.
•Moist inner surface – the inner surface of each alveolus
is moist so that oxygen can dissolve in the moisture
before diffusing across the alveolar wall.
•Surrounded by numerous blood capillaries – the blood
capillaries help to transport gases to and from the alveoli
quickly.

7. Detailed structure of alveolus

8. Mechanism of human breathing
•The breathing mechanism consists of two phases. The
taking in of air is called inhalation. The letting out of the
air is called exhalation.
Inhalation

9. • during breathing, the lungs expand and return to their
normal size to pump air into and out of them.
•The movements of the ribs and the diaphragm bring
about breathing.
Exhalation

10. Comparison of the mechanisms of
inhalation and exhalation
Inhalation Exhalation
•Diaphragm muscles contract.
•Diaphragm flattens out
•Diaphragm muscles relax.
•Diaphragm arches upwards
•Intercostal muscles contract. •Intercostal muscles relax.
•Ribcage moves upwards and
outwards.
•Ribcage moves downwards
and inwards.
•Volume of thoracic cavity
increases
•Volume of thoracic cavity
decreases.
•Air pressure surrounding the
lungs decreases.
•Air pressure surrounding the
lungs increases.
•Air flows into the lungs •Air is forced out of the lungs.

11. Composition of air in respiration
Content Inhaled air Exhaled air Alveolar air
Oxygen 21 % 16 % 14 %
Carbon
dioxide 0.04 % 4 % 6 %
Nitrogen 79 % 79 % 80 %
Water vapour Variable Saturated Saturated
Temperature Variable 34 ° C 37° C

12. •The changes in the content of air entering the lungs
are due to gas exchange in the alveoli.
Common mistake
-There is more carbon dioxide than oxygen in
exhaled air.
The Truth
- Exhaled air contains 16 % oxygen, 4 % carbon
dioxide and 79 % nitrogen.

13. The diffusion of oxygen from the alveoli into the
blood capillaries
•During inhalation, air is taken into the lungs
through the nasal cavity, passing through the
trachea, bronchi, bronchioles and finally alveoli.
•The air that reaches the alveoli is called alveolar
air. It is rich in oxygen and poor in carbon dioxide.
•The blood that reaches the capillaries
surrounding the alveoli is poor in oxygen and rich
in carbon dioxide.

14. •Gas exchange takes place in the lungs by
diffusion.
•Oxygen diffuses from the alveoli into the red
blood cells in the capillaries.
•At the same time, the red blood cells in the
capillaries release carbon dioxide which diffuses
into the alveoli.

16. •Red blood cells contain the oxygen – carrying
pigment called hemoglobin.
•Oxygen combines with hemoglobin to form
oxyhaemoglobin.
•The blood cells are transported around the
body.

18. •Gas exchange also takes place between the
capillaries and the body cells.
•Capillaries have a higher concentration of
oxygen than the body cells.
•Body cells have a higher concentration of
carbon dioxide than the capillaries.
•Oxyhaemoglobin releases oxygen which
diffuses into the body cells.
•Carbon dioxide diffuses into the blood at the
same time.

21. The importance of a Healthy Respiratory System
Substances harmful to the respiratory system
•The quality of the air can have significant effects on our
respiratory system.
•As air moves into our lungs, harmful substances in the
air may enter too. These harmful substances can cause
disease or even death.
•Air pollutants include smoke of cigarettes, gases from
the industries, exhaust of engines and haze.

22. Harmful substances in air pollutants
Air pollutant Harmful substances
Cigarette Smoke Nicotine, Tar
Gases from Factories
Sulphur dioxide, Nitrogen
Dioxide
Exhaust Fumes Carbon Monoxide
Haze Smoke, Dust

23. Cigarette Smoke Gases from Factories
Exhaust Fumes Haze

24. The effects of harmful substances on the
respiratory system
•Nicotine
a. Nicotine is a drug that causes addiction to
cigarette smoking.
b. Nicotine causes rapid heartbeat, increased blood
pressure and rapid breathing.
c. The disease related

25. •Tar
a. Tar contains carcinogens (substances that
cause cancer).
b. Tar also irritates the respiratory tract, causing
smoker’s cough.
•Sulphur dioxide
a. Exposure to sulphur dioxide can cause the
irritation of the respiratory system.
b. It can cause temporary or permanent
damage to the lungs

26. •Carbon monoxide
a. Carbon monoxide combines with haemoglobin in the
blood faster than oxygen can, hence it is poisonous gas
which causes suffocation.
• Low concentration of carbon monoxide can cause
dizziness, headache and fatigue whereas high
concentrations can fatal.

27. •Particular matter (fine particles in the air)
a. Continuous exposure to particulate matter causes
coughing, nasal congestion, watery nose, constant
sneezing and chest pain.
b. Those who are very likely to be affected by haze are
children, the elderly and people with illnesses like
asthma, bronchitis and pneumonia.

28. Diseases of the Respiratory System
Asthma Heart disease

29. Asthma
•This disease is caused by the narrowing of the fine
airways (bronchi and bronchioles) due to the contraction of
muscles in their walls. This is perhaps because of
sensitivity to air pollutants including smoke.
•A patient will find it different to breathe, wheezing and
feeling tightness in the chest.

30. Heart disease
•Nicotine raises the blood pressure and increase the level
of “bad” cholesterol in the blood.
•This makes a smoker more likely to suffer from a stroke
or a heart attack.

31. Bronchitis
•Chronic bronchitis can be defined as a condition
characterized by recurrent or chronic cough every day
over a period of several months.
•This disease is caused by the inflammation of the lining
of the bronchioles. This may be due to infection by
bacteria or viruses, or chemicals such as those found in
tobacco smoke.
•Smokers cough is an early sign of chronic bronchitis.
•In severe cases, the patient may turn blue which is
specially noticeable at the lips and fingers due to poor
oxygenation of blood.

32. Bronchitis

33. Lung cancer
•This disease is caused by a change in the cells inside the
lungs such that they divide out of control and produce
lumps of cells (tumours)
Which interfere with the normal functions of the lungs.
•90% of lung cancer patients have been heavy smokers.
•The risk of developing this disease is directly related to
the amount of tar that gets into the lungs.
•Lung cancer may not have any symptoms. When it is
detected, the cancer cells may have spread from the
lungs to other organs.

34. Lung cancer

35. •Emphysema is a condition in which the structure of the
alveoli is broken down by coughing. This reduces the
surface area for gas exchange.
Emphysema

36. Ways to improve air quality
Improving indoor air quality
•Avoid smoking indoors
•Make sure there is a steady supply of fresh air.
•Minimize air conditioning use
•Keep carpets and floor dust free
•Maintain a low humidity to prevent mould growth.

37. Improving outdoor air quality
•Avoid open burning of leaves and trash
•Do not allow cars or other motor vehicles idle for more
than a minute.
•Walk, ride a bicycle, car pool or use public
transportation.
•Keep the motor vehicle well maintained and use a fuel –
efficient vehicle.
•Reduce, reuse and recycle waste materials.
•Implement laws and regulations to control air pollution.