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Chapter 1RESPIRATIONHuman need oxygen in the air to live. Oxygen
is required during breathing. We will be healthy and active if we
get clean air to breathe. What is the function of oxygen in our
body?
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1.1 Human Breathing MechanismBreathing is a physical process in
which air is inhaled or taken in and exhaled or given out by a
living body.The system that helps human to breathe is the human
respiratory system.
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The Human Respiratory System3. Parts of the humanrespiratory
system are:Nasal
cavityTracheaBronchusBronchiolesAlveolusLungsDiaphragm
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The Structure of the LungsAlveolus (air sacs)
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4. Each alveolus is surrounded by a network of thin-walled blood
vessels called capillaries.bronchiolecapillariesair sacAlveolus
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Mechanism of human breathingThe breathing mechanism consists of
two phases. The taking in of air is called inhalation. The letting
out of air is called exhalation.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.
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During inhalation, the rib cage moves upwards and outwards. The
diaphragm contracts, move downwards and flattens. The thoracic
becomes bigger and causing the air pressure to decrease. The higher
air pressure outside forces the air into the lungs.Inhalation
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During exhalation, the rib cage moves downwards and inwards. The
diaphragm expands and curve upwards. The thoracic becomes smaller
and causing the air pressure to increase. The higher air pressure
in the lungs forces the air out.Exhalation
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Detailed structure of alveolusAir movementAlveolar wall
(one-cell thick)Exit of bloodEntry of bloodThin layer of
moistureRed blood cellCapillary
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Adaptation of the alveoli for efficient gas exchange1. Large
surface area to provide a large surface area for gas exchange2.
Very thin walls as one-cell thick to provide a very short distance
for the diffusion of gases.3. Moist inner surface so that oxygen
can dissolve easily.4. Surrounded by many blood capillaries that
help to transport gases to and from the alveoli quickly.
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1.2 Transport of Oxygen in the Human BodyDuring inhalation, air
is taken into the lungs through the nasal cavity, through the
trachea, bronchi, bronchioles and finally alveoli.The air that
reaches the alveoli is rich in oxygen and poor in carbon dioxide.
The movement of oxygen from the alveolus into blood capillaries
involves diffusion.Diffusion is the movement of molecules from a
region of higher concentration of the molecules to a region of
lower concentration of the molecules.
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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.
Red blood cells contain the oxygen-carrying pigment called
haemoglobin.Oxygen combines with haemoglobin to form
oxyhaemoglobin.The blood containing oxyhaemoglobin is transported
from the lungs to other parts of our body.
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Gas exchange also takes place between the capillaries and the
body cells.Oxygen has a higher concentration in the capillaries
than in the body cells.Carbon dioxide has a higher concentration in
the body cells than in the capillaries.Oxyhaemoglobin releases
oxygen which diffuses in the body cells.Carbon dioxide diffuses
into the blood at the same time.
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1.3 The Importance of A Healthy Respiratory System
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The substances which are harmful to the respiratory systemThe
air that we breathe in may contain substances which are harmful to
our respiratory system.For example,
Air pollutantHarmful substances Cigarette smokeNicotine, tar,
carcinogens, irritants, carbon monoxideGases from factoriesSulphur
dioxide, nitrogen dioxideExhaust fumesCarbon monoxideHaze Smoke,
dust
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Effects of harmful substances on the respiratory systemNicotine
a. Nicotine is the drug that causes addiction to cigarette smoking.
b. Nicotine causes rapid heartbeat, increased blood pressure and
rapid breathing. c. The diseases related to nicotine include
emphysema, heart disease and stroke.
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2. Tar a. Tar contain carcinogens (substance that cause cancer).
b. Tar blackens the lungs and irritates the respiratory tract,
causing smokers cough.
3. Sulphur dioxide a. The burning of coal and oil at factories
and power station emits SO2. b. Exposure to SO2 can cause
irritation of the respiratory system, coughs, breathing
difficulties, bronchitis and lung cancer.
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4. Carbon monoxide a. It commonly found in the smoke vehicles.
b. Low concentration of CO can cause dizziness, headaches and
fatigue whereas high concentration can be fatal.
5. Haze a. Continuous exposure can cause coughing, nasal
congestion, watery nose, constant sneezing and chest pain. b. It
can cause illness like asthma, bronchitis and pneumonia.