Common Requirements of living things ANIMALS – Chapter 5
Pt C: Exchanging Gases
Exchanging gases with the
environment
• All organisms must exchange gases
with their environment, usually oxygen
and /or carbon dioxide.
• Some unicellular and small
multicellular organisms and plants can
easily and directly exchange gases
with their environment.
• Larger animals have a many more cells
and a higher metabolic rate . They
require highly developed gas exchange
systems.
Respiratory Surfaces
Respiratory Surfaces for Gaseous exchange
Characteristics of Efficient Respiratory Surfaces
• Passive diffusion of gases from high concentration to lower
concentration
• Large surface area,
• Thin
• Moist
• Vascularised
• Water ventilation- Gills
– Supported by water and skeletal rod.
– In axolotles water passes over the
external gill surface due to water
currents and physical movement.
– In fish water flows through the mouth
of the fish and then is pushed over the
Internal gills when the mouth is
closed.
– Fish gills have counter current flow.
Water goes one way and the blood the
other way.
– Fish extract 80-90% of oxygen from
water, mammals only extract 25%
from air, (however air has a lot more
oxygen than water).
Ventilation of Fish Gills
When the fish’s mouth is open, the operculum closes and water is drawn into
the fish’s mouth. Conversely, when the fish closes its mouth, the operculum
opens and fresh water is then allowed to flow across the gills.
Ventilation of Lungs
• Breathing air requires less energy than
breathing water.
• There is much more oxygen in air than
in water. (21% )
• Disadvantages of breathing air are
water loss, because water evaporates
continuously.
• Enclosing the respiratory surface in the
body protect them from physical
damage and reduces water loss.
Grasshopper Respiratory system
• Tracheal system: involves the diffusion
of oxygen directly from the atmosphere
into the air-filled tubes.
• diffusion through air is more efficient
than the diffusion through water
(300,000 times more) or tissues
(1,000,000 times more).
Ventilation of Human Lungs
Human ventilation narrated animation
Ventilation- Respiration
Tidal Volume:
• The volume of air moved in and out of your lungs in each breath.
• When we breath in and out we never fully empty our lungs there is always
some stale air left over in the lungs, in our next breath we take this stale air
back in.
• This stale air and a fluid called surfactant which covers the alveolar surface,
protect the alveoli from collapsing in on themselves.
Lung Volumes
Pulmonary Circulation
Gas exchange in mammals
• Air is drawn in through the pharynx
• Air then passes into the trachea,
paired bronchi and branching
bronchioles.
• Both the trachea and the bronchi
have ciliated cells on their surface
and they secrete mucus, which
protects the lungs against dust and
bacteria.
• Finally air enters the air sacs called
alveoli, it is here that gaseous
exchange occurs
• The alveoli is made up of only 1
layer of cells which is covered in
blood capillaries.
http://www.nlm.nih.gov/medlinep
lus/ency/anatomyvideos/000059.h
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Gas exchange in lungs and
tissues animated overview
Transporting Gases
• Oxygen diffuses into the capillaries
surrounding the alveoli & carbon dioxide
diffuses from the capillaries into the alveoli.
• The blood transports gases around the body.
• Gases are transported either attached to the
red pigment haemoglobin or dissolved in blood
plasma
• Each iron containing molecule of haemoglobin
can attach to 4 oxygen molecules.
gaseous exchange
•
When cellular respiration occurs, carbon
dioxide is produced as a waste product this
must be released if not to cause changes in
pH of the blood and tissue fluids.
Carbon dioxide is transported in 3 ways:
1. Dissolved carbon dioxide
Carbon dioxide is much more soluble in blood than
oxygen and dissolves in the plasma. Approx 5 %
2.
Bound to haemoglobin & plasma protein
Carbon dioxide combines reversibly with
haemoglobin to form carbaminohaemoglobin.
Carbon dioxide binds to amino groups on the
polypeptide chains of haemoglobin and plasma
proteins. Approx 10 %
3.
Bicarbonate ions
Approx 85% of carbon dioxide is transported as
bicarbonate ions (HCO3-) and hydrogen ions (H+).
Composition of Inspired v Expired Air
Composition of atmospheric air and expired air in a typical subject.
Note that only a fraction of the oxygen inhaled is taken up by the lungs.
Component
Atmospheric Air (%)
Expired Air (%)
N2 (plus inert gases)
78.62
74.9
O2
20.85
15.3
CO2
0.03
3.6
H2O
0.5
6.2
100.0%
100.0%