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2. LE A RNING OUTC OME S
 To describe the change in the rate of respiration
after completing a vigorous activity;
 To correlate the rate of respiration with the oxygen
& carbon dioxide content in the body;
 To explain the regulatory mechanism of oxygen &
carbon dioxide content in the body;
 To explain the human respiratory response & rate
of respiration in different situations;
 To correlate the respiration with the rate of heart
beat.
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3.  At rest : breathing rate of man –
15 to 18 times a minute.
 At work @ vigorous activity :
increases  more O2 is needed
to supply enough energy, more
CO2 is produced from cell
respiratory in the muscles
 The increased conc. of CO2 in
the blood  the regulatory
mechanism  rate of breathing
increase  O2 is supplied
quickly to the body cells, CO2 is
removed rapidly from the lungs
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4. Regulatory Mechanism of O2
& CO2 Content in the Body
 The breathing centre of humans is
located in the medulla oblongata of
the brain. Consist of a special group
cells called central chemoreceptors 
regulate the O2 & CO2 content in the
body
 Vigorous activity (swimming & aerobic
exercises) – the [CO2] in the blood
increases because of the increased
rate of respiration in the cells
 PCO2 in the blood increase while PO2
decrease
 The carotid & aortic bodies are
stimulated  nerve  inspiratory
centre
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5.  High [CO2] in the blood
lowers the pH value (carbonic
acid  hydrogen ions +
bicarbonate ions)
 High [H+] (low pH) 
stimulates the central
chemoreseptors to emit nerve
impulses 
breathing/inspiratory centre
 impulses  intercostal
muscles & diaphragm muscles
 The intercostal muscles & the
diaphragm muscles contract
rapidly  the rate of
breathing & the rate of
ventilation increase.
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6.  The lung expand, stretch
receptor in the wall of bronchi
& bronchioles are stimulated 
nerve  expiratory centre 
‘switch off’ inspiratory centre
 Diaphragm & external
intercostal relax  expiration
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7.  The rate of ventilation = vol. of air
breathed per minute & signifies the depth
of breathing  the rate of gaseous
exchange between the air in the alveolus
& the blood in the capillaries.
 Enable more O2 to be supplied & more
CO2 to be removed until the level of pH in
the blood returns to normal
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8. Respiratory Response in Difference
At high altitudes
Situations
 4000m above sea level, 40% less O2  develop hypoxia (a
shortage of O2)
 Mountain sickness (breathless, headache, nausea, vomiting
& heart palpitations)
 Chemoreceptors (carotid & aortic bodies) send nerve to the
medulla oblongata  increase the rate of respiration & the
rate of heartbeat  acclimatised
Fear
 Fear/ feeling anxious, the rate of breathing & the rate of
heartbeat will increase
 The adrenal glands secrete the hormone adrenaline into the
bloodstream  target organ  prepare the body action
 Enable muscles to obtain enough oxygen & to remove the
excess CO2 quickly
 Provide enough energy to prepare the body to act under
such tense situations 8

9. 7.5 The Importance of Maintaining
a Healthy Respiratory System
 Do not smoke  bronchitis, emphysema &
lung cancer
 Keep away from smokers to avoid 2nd hand
smoke  lung diseases
 Haze – stay indoors or cover your nose &
mouth with a mask
 Exercise to keep lungs healthy  breathe
deeply, lungs become stronger & better at
supplying body with O2
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15. W h a t is in t o b a c c o
s moke ?
 Tar
Tar
 Thick, sticky dark brown substance –
carcinogenic, damages lungs tissues,
breakdown the alveoli (decreasing the total
surface area)  causes bronchitis, smoker
cough
 Nicotine
 Highly addictive chemical – causes blood
platelets to become sticky (lead to
clotting), raise up blood pressure & heart
rate, narrows the arteries  HBP
 Carbon monoxide
 Combine Poisonous, odorless with
haemoglobin  carboxyhaemoglobin
 Limits the body’s ability to transport O2 
breathlessness 15

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