3. 1.1 Human Breathing
Mechanism
1) Human Respiratory System
Living organisms must be able to take
oxygen from the air and get rid of carbon
dioxide to the air.
Swapping oxygen for carbon dioxide in this
way is called gas exchange.
Gas exchange takes place through a gas
exchange surface also known as a
respiratory surface.
4. For gas exchange we need a respiratory
system.
Breathing is an external respiration.
Breathing consist of two stage:
1. Inhalation: air is taken into the lungs
2. Exhalation: air is passes out of the lungs
5. STRUCTURES OF THE
RESPIRATORY SYSTEM
The breathing system or the human respiratory
system consists of the following structures:
1. The nasal cavity
2. Trachea
3. Bronchus
4. Bronchiole
5. Lungs
6. Rib cage
7. Diaphragm
8. The intercostals muscles
6. Structure of the human respiratory system:
Nasal cavity
Trachea
Nose
Mouth
Heart
Alveoli
Diaphragm
Bronchioles
Bronchus
Intercostals
muscles
Lung
7.
8. Structure of the lung
The lungs are the respiratory organs.
We have a pair of lungs in the thoracic
cavity.
They are protected by the rib cage.
9. The lungs are connected to the trachea by
two tubes. These tubes are right bronchus
and left bronchus.
The bronchus divide into smaller tubes called
bronchioles.
10. The bronchioles end in clusters of tiny air
sacs known as alveoli, in the lungs.
11. Flow of air into the lungs:
Air is breathed in through the nose and enters the
nostrils.
The nostrils leads to the nasal cavity. While passing
through the nasal cavity the air is warmed up and
moistened.
Hairs and sticky mucus trap particles inside the nasal
cavity. The clean air then enters to the trachea.
The trachea branches into two bronchi.Eachs bronchus
leads directly into a lung.
The bronchus branches into bronchioles.
Each bronchiole end in a cluster of air sacs called
alveoli/alveolus.
The wall of the alveolus is only one-cell thick. It is thin,
moist and surrounded by a network of capillaries.
The exchange of respiratory gases occurs between the
alveolus and capillaries.
12. The path of air into the lungs is summarized:
Nasal cavity Trachea
BronchioleAlveolus
Bronchus
13. The breathing mechanism
Breathing mechanism involves:
1. Inhalation (breathing in)
2. Exhalation (breathing out)
During inhalation:
1. The intercostals muscles and the diaphragm
contract.
2. The diaphragm moves down wards, increasing the
volume of the thoracic cavity.
3. The intercostals muscles pull the ribs up, expanding
the ribs and further increasing the volume of the
thoracic cavity.
4. These actions lower the air pressure in the alveoli.
5. Air from the outside then rushes in through the nasal
cavities, trachea and lungs. The lungs expand.
14. During exhalation:
1. The intercostals muscles relax causing the rib
cage to move downwards and inwards.
2. At the same time, the muscles of the diaphragm
relax. The diaphragm curves upwards and returns
to its original dome shape.
3. These action return the thoracic cavity to its
original volume. The air pressure inside the lungs
is now higher than the atmospheric pressure
outside.
4. The lungs contract and the air is forced out
through the respiratory tract.
15. Comparison between inhalation and
exhalation:
Inhalation Aspect Exhalation
Diaphragm
Movement of rib
cage and the
wall of the
thoracic cavity
Contract, flattens
and is pushed
downwards
Relaxes and is
pushed upwards.
Move upwards
and outwards.
Move
downwards and
inwards.
16. Inhalation Aspect Exhalation
Volume of
thoracic cavity
Air pressure in
the thoracic
cavity
Movement of
air
Increases Decreases
Decreases Increases
From the
atmosphere to
the lungs
From the lungs to
the atmosphere
17. Exercise 1.1
1. Name all parts in the human respiratory
system.
2. Trace the flow of inhaled air through the
nostrils to the lungs
Nasal cavity,trachea,bronchus,lungs,rib
cage,diaphragm and the intercostals muscles.
Nasal cavity Trachea
Bronchiole Alveolus
Bronchus
18. 3. Explain how the diaphragm and the
intercostals muscles force air out from the
lungs.
The diaphragm muscles relax and move up
and at the same time the intercostals muscles
pull the ribs downwards and inwards. These
actions cause the air to flow out of the lungs.
19. 1.2 Transport of Oxygen in the
Human Body
1. Diffusion of oxygen from the
alveolus to the capillaries.
The exchange of gases occurs by
diffusion in the alveoli.
Diffusion is the movement of molecules
from a region where they are highly
concentrated to a region where they are
less concentrated.
20. The characteristics enable oxygen to
diffuse through the walls of the
alveoli easily and efficiently
1. Have very large surface areas and
2. Thin walls (only one- cell thick).
3. The inner surfaces of the alveoli are always
moist.
4. The outer surfaces of the alveoli are surrounded
by a network of blood capillaries.
21. Inhaled air is rich in oxygen.
The oxygen concentration in the alveolus higher
than the oxygen concentration in the
deoxygenated blood in the capillaries.
The difference in oxygen concentration makes
the oxygen diffuse easily into the blood
capillaries.
22. Oxygen in the alveolus diffuses through
the walls into the blood.
Carbon dioxide and water vapour diffuse
from the blood into the alveolus.
25. 2. Oxygen transport
Haemoglobin in the red blood cell needs to
carry oxygen from the lungs to all parts of the
body.
Haemoglobin is a blood pigment.
As the oxygen concentration is high in the
alveolus, oxygen diffuses into the capillaries.
Oxygen then combines with haemoglobin in
the red blood cells and forms oxyhaemoglobin.
26. 3. Diffusion of oxygen from the capillaries to the body
cells
When blood reaches the body cells, oxyhaemoglobin is
broken down into haemoglobin and oxygen.
The oxygen then diffuses through the walls of the
capillaries into the cells.
Oxygen is then used to oxidise food to release carbon
dioxide during cell respiration.
At the same time,carbon dioxide from the cells diffuses
into the capillaries to be carried back to the lungs.
27. Exercise 1.2
1. What process is involved in the exchange of
gases in the alveolus?
2. Which gases are exchanged in the
alveolus?
The movement of gases through the wall of
the alveolus is known as diffusion
Oxygen and carbon dioxide
28. 3. What are the two characteristics of the
alveolus which enable it to function
efficiently?
4. Why are the alveoli in the lungs surrounded
by blood capillaries?
i. Has a very large surface area.
ii. Has a thin wall which is one-cell thick.
This is to allow oxygen in the alveolus to enter the blood
in the capillaries and carbon dioxide from the blood in the
capillaries to diffuse into the alveolus.
30. 1.3 The importance of a
healthy respiratory system
1. Effects of harmful substances:
i. Nicotine in cigarettes cause the following
effects:
a) Stimulates the production of cells in the
trachea and lungs and leads to lung cancer.
b) Narrows and hardens the blood vessels.
This affects blood flow and causes heart
attacks.
31. ii. Tar in tobacco is carcinogenic and can cause lung
cancer.
iii. Nitrogen dioxide in cigarette smoke forms an acid
which can destroy lung tissues.
iv. Sulphur dioxide is very soluble in the alveoli and it
forms an acid which destroys the lungs.
v. Carbon monoxide is a toxic gas, combines with
haemoglobin in the red blood cells and prevents
oxygen from combining with haemoglobin.
vi. Dust and dirt can hinders the exchange of gases.
32. 2. Diseases of the respiratory system:
Air pollution, the presence of harmful
microbes in air, smoking and crowded cities
cause respiratory diseases. Examples
include asthma, influenza, pneumonia,
tuberculosis, bronchitis, emphysema and
lung cancer.
Asthma: condition in which the tubes of the
lungs become inflamed. This is because the
air tubes are narrower and partially blocked.
33. Diseases of the respiratory system
Asthma
Influenza
Pneumonia
Tuberculosis
Bronchitis
Emphysema
Lung cancer
34. Influenza: cause by viruses which attack the
mucus membranes in the respiratory system.
Symptoms: Blocked nose, teary eyes,
headache, aches in the limbs, cough and
fever.
Pneumonia: caused by bacteria, viruses and
chemical substances in polluted air. The
lungs are filled with pus and fluid.
Symptoms: chest pain, fever and cough.
35. Tuberculosis: caused by bacterial infection
which are carried by water droplets and dust
in the air.
Symptoms: prolonged cough and spit out
blood in the end stages.
Bronchitis: caused by viral infections.
Symptoms: cough, produce a lot of mucus,
colds and phlegm. Makes respiration and
gaseous exchange difficult.
36. Emphysema: This disease is linked to
smokers and people who work in dust areas.
The patient experiences breathing difficulties.
Lung cancer: Cause by smoking cigarettes.
Air polluted with carcinogen from factories
and vehicle emissions, dust and asbestos
also cause lung cancer.
37. 3. Improving Air Quality
Pollution is mainly caused by irresponsible
human behavior and improperly planned
activities.
We must be responsible for preserving and
conserving air quality.
Air pollution interferes with the respiratory
process.
It can cause respiratory diseases which can be
fatal.
38. To preserve and conserve the quality of air
we must:
1. Support and campaign against open
burning of rubbish.
2. Give up the habit of smoking.
3. Reduce the number of vehicles on the road.
4. Avoid the burning of forest for agriculture,
housing and industries.
39. Exercise 1.3
1. Name 4 respiratory diseases caused by
pollutants in the air.
2. Why does a person feel sick and dizzy after
inhaling carbon monoxide?
Asthma, bronchitis, emphysema and lung
cancer.
Carbon monoxide combines with haemoglobin in
the blood.This prevent oxygen from combining
with haemoglobin.Oxygen cannot be transported
to the body cells that need it.This makes a
person feels sick and dizzy.
40. 3. Name four dangerous chemical substances
in cigarette.
4. State two human activities which can help to
reduce air pollution.
Nicotine,tar,carbon monoxide and hydrogen
cyanide.
Stop open burning of rubbish and use public
transport to help reduce pollutants and keep
the air clean.
