Download Chapter 22

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People cannot survive in the air at the world’s
highest peaks in the Himalayan Mountains
Twice a year, flocks of geese migrate over the
Himalayas
How can geese fly where people cannot breathe?
Copyright © 2009 Pearson Education, Inc.
MECHANISMS
OF GAS EXCHANGE
Copyright © 2009 Pearson Education, Inc.
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Three phases of gas exchange
1. Breathing
2. Transport of oxygen and carbon dioxide in blood
3. Body tissues take up oxygen and release carbon
dioxide
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Cellular respiration requires a continuous
supply of oxygen and the disposal of carbon
dioxide
Copyright © 2009 Pearson Education, Inc.
O2
1
Breathing
CO2
Lung
Circulatory
system
2
Transport
of gases by
the circulatory
system
Mitochondria
3
Exchange
of gases
with
body
cells
O2
CO2
Capillary
Cell
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Respiratory surfaces must be thin and moist for
diffusion of O2 and CO2
Cut
Cross section
of respiratory
surface (the
outer skin)
Body surface
Respiratory
surface
(gill)
CO2
O2
Capillaries
CO2
O2
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Capillary
Body surface
CO2
CO2
O2
Respiratory
surface
(within lung)
O2
Capillary
–
Tetrapod adaptation: Fossil fish with legs
had lungs and gills
– Legs may have helped them lift up to gulp air
– The fossil fish Tiktaalik illustrates these airbreathing adaptations
Copyright © 2009 Pearson Education, Inc.
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From the nasal cavity,
air next passes to…
Nasal
cavity
Pharynx
(Esophagus)
Larynx
Left lung
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
(Heart)
Copyright © 2009 Pearson Education, Inc.
Oxygen-rich
blood
Nasal
cavity
Pharynx
(Esophagus)
Larynx
Oxygen-poor
blood
Bronchiole
Alveoli
Left lung
Trachea
Right lung
Bronchus
Blood
capillaries
Bronchiole
Diaphragm
(Heart)
Oxygen-rich
blood
Oxygen-poor
blood
Bronchiole
Alveoli
Blood
capillaries
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Alveoli are well
adapted for gas
exchange
– High surface area of
capillaries
– High surface area of
alveoli
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Oxygen-rich
blood
Oxygen-poor
blood
Bronchiole
Alveoli
In alveoli
– O2 diffuses into the
blood
– CO2 diffuses out of
the blood
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Blood
capillaries
Why is smoking is a serious assault on
the respiratory system?
1. Damages cilia and decreases mucus production
in the respiratory passages
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1. Damages cilia and decreases mucus production
in the respiratory passages
2. And also…
– Increases the risk of heart attacks and strokes
(increases heart disease)
– Raises blood pressure
– Increases harmful types of cholesterol
– Causes lung cancer (90%)
– Causes emphysema
Copyright © 2009 Pearson Education, Inc.
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Every year in the United States, smoking kills
about 440,000 people
– This is more than all the deaths from accidents,
alcohol, drug abuse, HIV, and murders combined

Adults who smoke cut 13–14 years from their
lifespan
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Lung
Heart
How is breathing controlled?
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Breathing is usually under automatic control=
breathing control center in brain
As CO2 increases (and pH decreases) in blood 
rate of depth of breathing increases
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Cerebrospinal
fluid
Brain
Pons
1 Nerve signals
trigger contraction
of muscles
Diaphragm
Rib muscles
Medulla
Cerebrospinal
fluid
Brain
Pons
2 Breathing control
1 Nerve signals
trigger contraction
of muscles
Diaphragm
Rib muscles
Medulla
centers respond
to pH of blood
Cerebrospinal
fluid
Brain
Pons
2 Breathing control
1 Nerve signals
trigger contraction
of muscles
Medulla
centers respond
to pH of blood
3 Nerve signals
indicating CO2
and O2 levels
CO2 and O2
sensors in aorta
Diaphragm
Rib muscles
Copyright © 2009 Pearson Education, Inc.
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The heart pumps blood to two regions
– The right side pumps oxygen-poor blood to the
lungs
– The left side pumps oxygen-rich blood to the body
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In the lungs, blood picks up O2 and drops off
CO2
In the body tissues, blood drops off O2 and picks
up CO2
Copyright © 2009 Pearson Education, Inc.
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Gases move from areas of higher concentration
to areas of lower concentration
– Example: Gases in the alveoli of the lungs have
more O2 and less CO2 than gases the blood
– How does this happen??
– Diffusion down the pressure gradient
– Each gas exerts a pressure called partial
pressure
Copyright © 2009 Pearson Education, Inc.
What physically carries the
respiratory gasses in the blood?
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Most animals transport O2 bound to proteins
called respiratory pigments
– Iron-containing hemoglobin
– Is used by almost all vertebrates and many
invertebrates
– Transports oxygen, buffers blood, and transports
CO2
Iron atom
O2 loaded
in lungs
O2 unloaded
in tissues
Heme group
Polypeptide chain
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O2
O2
◦ A human fetus
– Does not breathe with its lungs
– Instead, it exchanges gases with maternal blood
in the placenta
◦ In the placenta, capillaries of maternal blood
and fetal blood run next to each other
– The fetus and mother do not share the same
blood
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Placenta, containing
maternal blood vessels
and fetal capillaries
Umbilical cord,
containing fetal
blood vessels
Amniotic
fluid
Uterus