This document discusses gaseous exchange and respiration. It describes: 1) How gaseous exchange occurs across the alveolus and blood capillaries in the lungs via diffusion of oxygen and carbon dioxide. 2) The transport of respiratory gases - oxygen is transported via hemoglobin in the blood, while carbon dioxide is transported through the blood in various forms like bicarbonate ions, carbaminohaemoglobin, and as carbonic acid. 3) Gaseous exchange between the blood and body cells - oxygen diffuses into cells due to higher blood pressure, while carbon dioxide diffuses out of cells into the blood for transport to the lungs.

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2. LEARNING
OUTCOMES
 To describe the process of gaseous
exchange across the surface of the alveolus
& blood capillaries in the lungs;
 To explain the transport of respiratory
gases;
 To explain the process of gaseous exchange
between the blood & body cells;
 To distinguish the composition of inhaled &
exhaled air. 2

3.  Gaseous exchange
occurs across the surface
of the alveolus & blood
capillaries in the lungs.
 Occurs by the process of
diffusion & involves
oxygen & carbon
dioxide.
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4. P roc e s s of G a s e ous
E x c h a n g e a t t h e A lv e o lu s
 Inhaled air in alveolus – more
oxygen, less carbon dioxide
compare to the qtts. in the blood
capillaries of the lung.
 The partial pressure of O2 is
higher in the air of the alveolus
compare to the partial pressure
of O2 in the blood capillaries.
 The higher partial pressure of
oxygen in the alveolus causes
the oxygen to dissolve in the
layer of moisture on the wall of
the alveolus & diffuse out of the
alveolus into the blood capillaries 4

5.  During respiration, CO2 is
produced. The blood
capillaries in the body
transport the CO2 to the
alveolus.
 The p ar tial p r e ssur e
o f CO 2 in the b l o o d
cap il l ar ie s entering the
alveolus is highe r than
the partial pressure of
CO2 in the alveolus
 The CO2 in the blood
capillaries diffuses out of
the blood capillaries into
the alveolus & is expelled
during exhalation.
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7. Transport of Respiratory
Gases
 The oxygen from the blood capillaries has to be
transported to the body cells that need it.
 The oxygen diffuses into the RBCs & combines with
haemoglobin to form oxyhaemoglobin.
Haemoglobin + Oxygen  Oxyhaemoglobin
 Transport from lungs to the whole body in the form
of oxyhaemoglobin
 Oxyhaemoglobin is not stable. The oxyhaemoglobin
breaks down & releases the oxygen to diffuse into
the cell 7

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9. Transport of Respiratory
 In the blood, someGases
CO2 is transported in the form
of carbonic acid
 Some are combines with haemoglobin to form
carbaminohaemoglobin in the RBCs.
 A large part of the CO2 is transported to the
alveolus in the form of bicarbonate ions in the
blood plasma.
 The CO2 are transported to the alveolus by these 3
ways.
 At the alveolus in the lungs, the CO2 is released
from its compound & diffuse into the alveolus, to be
expelled during exhalation 9

10. G a s e ous E xc ha ng e

abetween o d y capillariess body
Occurs
t B the blood C e l l &
cells
 The body cells - lack of O2, blood - high partial
pressure of O2  O2 diffuse out of the blood
capillaries into the body cells
 Body cells – high conc. of CO2  product of
cellular respiration
 Body cells – high partial pressure of CO2, blood –
low partial pressure of CO2  CO2 diffuses out of
the body cells into the blood capillaries
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11. C o m p o s it io n o f
In h a le d & E x h a le d A ir
Components of Inhaled air Exhaled air
air
Oxygen 21% 16%
Carbon dioxide 0.03% 4%
Nitrogen 78% 78%
Water vapour Varies (depends on More (usually
the humidity of air) saturated)
Dust particles Varies Usually none
Temperature Varies (follows Body temperature
(heat) atmospheric temp.) 11

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13. E X E R C IS E 7 . 3
 How different is the partial pressure of
oxygen & carbon dioxide between the
alveolar space & alveolar capillaries during
gaseous exchange? (2 marks)
 How different is the partial pressure of
oxygen & carbon dioxide in the blood
entering the alveolus with the blood leaving
the alveolus? (2 marks)
 How is oxygen transported in blood? (1
mark)
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14. Q U IZ 7 . 3
 Compound formed by binding of carbon
dioxide with haemoglobin.
 Compound formed by binding of carbon
monoxide with haemoglobin.
 Respiratory pigment in red blood cells.
 How many ways are CO2 transported in the
blood? List them.
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