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Chapter 22
Gas Exchange
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Introduction
 People cannot survive for long in the air at the
world’s highest peaks in the Himalayan Mountains.
 Yet twice a year, flocks of geese migrate over the
Himalayas.
 How can geese fly where people cannot breathe?
– Geese have more efficient lungs than humans, and
– their hemoglobin has a very high affinity for oxygen.
© 2012 Pearson Education, Inc.
Figure 22.0_1
Chapter 22: Big Ideas
Mechanisms of Gas
Exchange
Transport of Gases in the
Human Body
The Human
Respiratory System
Figure 22.0_2
MECHANISMS
OF GAS EXCHANGE
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22.1 Overview: Gas exchange in humans involves
breathing, transport of gases, and exchange
with body cells
 The process of gas exchange is sometimes called
respiration, the interchange of
– O2 and the waste product CO2
– between an organism and its environment.
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22.1 Overview: Gas exchange in humans involves
breathing, transport of gases, and exchange
with body cells
 Three phases of gas exchange occur in humans
and other animals with lungs:
1. breathing,
2. transport of oxygen and carbon dioxide in blood, and
3. exchange of gases with body cells.
– Body tissues take up oxygen and
– release carbon dioxide.
 Cellular respiration requires a continuous supply of
oxygen and the disposal of carbon dioxide.
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Figure 22.1
O2
CO2
1
Lung
Breathing
Heart
Blood
vessels
2
Transport
of gases by
the circulatory
system
Capillary
3
Exchange of
gases with
body cells
Circulatory
System
Mitochondria
O2
CO2
Cell
22.2 Animals exchange O2 and CO2 across moist
body surfaces
 Respiratory surfaces must be
– moist for diffusion of O2 and CO2 and
– thin, to best facilitate diffusion.
 The skin may be used for gas exchange in animals
that are
– wet and
– small.
– Earthworms are an example.
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Figure 22.2A
Cross section of the
respiratory surface
(the outer skin)
CO2
O2
Capillaries
22.2 Animals exchange O2 and CO2 across moist
body surfaces
 Most animals have specialized body parts that
promote gas exchange:
– gills in fish and amphibians,
– tracheal systems in arthropods, and
– lungs in tetrapods that live on land, such as
– amphibians,
– reptiles including birds, and
– mammals.
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Figure 22.2B
Body surface
Respiratory
surface
(gills)
CO2
O2
Capillary
Figure 22.2C
Body surface
Respiratory
surface
(tips of tracheae)
O2
CO2
Body cells
(no capillaries)
Figure 22.2D
Body surface
CO2
CO2
Respiratory
surface
(within lung)
O2
O2
Capillary
22.3 Gills are adapted for gas exchange in aquatic
environments
 Gills
– are extensions of the body,
– increase the surface to volume ratio, and
– increase the surface area for gas exchange.
– Oxygen is absorbed.
– Carbon dioxide is released.
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22.3 Gills are adapted for gas exchange in aquatic
environments
 In a fish, gas exchange is enhanced by
– ventilation of the gills (moving water past the gills) and
– countercurrent flow of water and blood.
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22.3 Gills are adapted for gas exchange in aquatic
environments
 Gas exchange with water has its limits.
– Water holds only about 3% of the oxygen in air.
– Cold water holds more oxygen than warm water.
– Fresh water holds more oxygen than salt water.
– Turbulent water holds more oxygen than still water.
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Figure 22.3
Oxygen-poor
blood
Oxygen-rich
blood
Water
flow
Lamella
Blood vessels
Operculum
(gill cover)
Gill arch
Water flow
between
lamellae
Blood flow through
capillaries in a lamella
Countercurrent exchange
Water flow, showing % O2
Gill filaments
Diffusion
of O2 from
water
to blood
100
70
40
15
80
60
30
5
Blood flow in simplified
capillary, showing % O2
Figure 22.3_1
Water
flow
Blood vessels
Operculum
(gill cover)
Gill arch
Gill filaments
Figure 22.3_2
Oxygenrich
blood
Oxygen-poor
blood
Lamella
Countercurrent exchange
Water flow, showing % O2
Water flow
between
lamellae
Blood flow through
capillaries in a lamella
Diffusion
of O2 from
water
to blood
100 70
40
15
80
30
5
60
Blood flow in
simplified capillary,
showing % O2
22.4 The tracheal system of insects provides direct
exchange between the air and body cells
 Compared to water, using air to breathe has two
big advantages.
1. Air contains higher concentrations of O2 than water.
2. Air is lighter and easier to move than water.
 However, air-breathing animals lose water through
their respiratory surfaces.
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22.4 The tracheal system of insects provides direct
exchange between the air and body cells
 Insect tracheal systems use tiny branching tubes
that
– reduce water loss and
– pipe air directly to cells.
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Figure 22.4A
Tracheae
Air sacs
Tracheoles
Opening
for air
Body
cell
Tracheole
Air
sac
Trachea
O2
Body wall
CO2
Figure 22.4A_1
Tracheoles
Figure 22.4B
22.5 EVOLUTION CONNECTION:The
evolution of lungs facilitated the movement
of tetrapods onto land
 Tetrapods seem to have evolved in shallow water.
– Fossil fish with legs had lungs and gills.
– Legs may have helped them lift up to gulp air.
– The fossil fish Tiktaalik
– lived about 375 million years ago and
– illustrates these air-breathing adaptations.
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Figure 22.5
Shoulder bones
Neck
Eyes on top
of a flat skull
Fin
22.5 CONNECTION:The evolution of lungs
facilitated the movement of tetrapods onto
land
 The first tetrapods on land diverged into three major
lineages.
1. Amphibians use small lungs and their body surfaces.
2. Nonbird reptiles have
– lower metabolic rates and
– simpler lungs.
3. Birds and mammals have
– higher metabolic rates and
– more complex lungs.
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THE HUMAN RESPIRATORY
SYSTEM
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22.6 In mammals, branching tubes convey air to
lungs located in the chest cavity
 The diaphragm
– separates the abdominal cavity from the thoracic cavity
and
– helps ventilate the lungs.
 In mammals, air is inhaled through the nostrils into
the nasal cavity. Air is
– filtered by hairs and mucus surfaces,
– warmed and humidified, and
– sampled for odors.
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22.6 In mammals, branching tubes convey air to
lungs located in the chest cavity
 From the nasal cavity, air next passes
– to the pharynx,
– then larynx, past the vocal cords,
– into the trachea, held open by cartilage rings,
– into the paired bronchi,
– into bronchioles, and finally
– to the alveoli, grapelike clusters of air sacs, where gas
exchange occurs.
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Figure 22.6A
To the
heart
Nasal cavity
Left lung
Pharynx
(Esophagus)
Oxygen-rich
blood
From the
heart
Oxygen-poor
blood
Bronchiole
Larynx
Trachea
CO2
O2
Right lung
Bronchus
Bronchiole
Alveoli
Blood
capillaries
Diaphragm
(Heart)
Figure 22.6A_1
Nasal cavity
Left lung
Pharynx
(Esophagus)
Larynx
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
(Heart)
Figure 22.6A_2
To the
heart
Oxygen-rich
blood
From the
heart
Oxygen-poor
blood
Bronchiole
CO2
O2
Alveoli
Blood
capillaries
22.6 In mammals, branching tubes convey air to
lungs located in the chest cavity
 Alveoli are well adapted for gas exchange with high
surface areas of capillaries.
 In alveoli,
– O2 diffuses into the blood and
– CO2 diffuses out of the blood.
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Figure 22.6B
22.6 In mammals, branching tubes convey air to
lungs located in the chest cavity
 Surfactants are specialized secretions required to
keep the walls of the small alveoli from sticking
shut.
– Babies born 6 weeks or more before their due date
often struggle with respiratory distress syndrome due to
an inadequate amount of lung surfactant.
– Artificial surfactants are now administered to preterm
infants.
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22.6 In mammals, branching tubes convey air to
lungs located in the chest cavity
 Exposure to pollutants can cause continual
irritation and inflammation of the lungs.
– Examples of common lung pollutants include
– air pollution and
– tobacco smoke.
– Chronic obstructive pulmonary disease (COPD) can
result, limiting
– lung ventilation and
– gas exchange.
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22.7 CONNECTION: Smoking is a serious assault
on the respiratory system
 Mucus and cilia in the respiratory passages
– sweep contaminant-laden mucus up and out of the
airways and
– can be damaged by smoking.
 One of the worst sources of lung-damaging air
pollutants is tobacco smoke, containing more than
4,000 chemicals.
 Without healthy cilia, smokers must cough to clear
dirty mucus from the trachea.
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22.7 CONNECTION: Smoking is a serious assault
on the respiratory system
 Smoking can cause
– lung cancer,
– cardiovascular disease, and
– emphysema.
 Smoking accounts for 90% of all lung cancer cases.
 Smoking increases the risk of other types of cancer.
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22.7 CONNECTION: Smoking is a serious assault
on the respiratory system
 Smoking also
– increases the risk of heart attacks and strokes,
– raises blood pressure, and
– increases harmful types of cholesterol.
 Every year in the United States, smoking
– kills about 440,000 people,
– more than all the deaths from accidents, alcohol, drug
abuse, HIV, and murders combined.
 Adults who smoke die 13–14 years earlier than
nonsmokers.
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Figure 22.7
Lung
Heart
22.8 Negative pressure breathing ventilates your
lungs
 Breathing is the alternate inhalation and exhalation
of air (ventilation).
 In mammals, inhalation occurs when
– the rib cage expands,
– the diaphragm moves downward,
– the pressure around the lungs decreases, and
– air is drawn into the respiratory tract.
– This type of ventilation is called negative pressure
breathing.
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Figure 22.8
Rib cage
expands as
rib muscles
contract
Air
inhaled
Rib cage
gets smaller
as rib muscles
relax
Air
exhaled
Lung
Diaphragm
The diaphragm contracts
(moves down)
The diaphragm relaxes
(moves up)
Inhalation
Exhalation
22.8 Negative pressure breathing ventilates your
lungs
 Exhalation occurs when
– the rib cage contracts,
– the diaphragm moves upward,
– the pressure around the lungs increases, and
– air is forced out of the respiratory tract.
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22.8 Negative pressure breathing ventilates your
lungs
 Not all air is expelled during exhalation.
– Some air still remains in the trachea, bronchi,
bronchioles, and alveoli.
– This remaining air is “dead air.”
– Thus, inhalation mixes fresh air with dead air.
 One-way flow of air in birds
– reduces dead air and
– increases their ability to obtain oxygen.
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22.9 Breathing is automatically controlled
 Breathing is usually under automatic control.
 Breathing control centers in the brain sense and
respond to CO2 levels in the blood.
 A drop in blood pH increases the rate and depth of
breathing.
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Figure 22.9_s1
Brain
1
Nerve signals
trigger contraction
of the rib muscles
and diaphragm.
Diaphragm
Rib muscles
Cerebrospinal
fluid
Medulla
Figure 22.9_s2
Brain
Cerebrospinal
fluid
2
1
Nerve signals
trigger contraction
of the rib muscles
and diaphragm.
Diaphragm
Rib muscles
Medulla
Breathing control
center responds
to the pH of blood
and cerebrospinal fluid.
Figure 22.9_s3
Brain
Cerebrospinal
fluid
2
1
Nerve signals
trigger contraction
of the rib muscles
and diaphragm.
Medulla
Breathing control
center responds
to the pH of blood
and cerebrospinal fluid.
3
Nerve signals
indicate CO2
and O2 levels.
CO2 and O2
sensors in the aorta
Heart
Diaphragm
Rib muscles
TRANSPORT OF GASES
IN THE HUMAN BODY
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22.10 Blood transports respiratory gases
 The heart pumps blood to two regions.
1. The right side pumps oxygen-poor blood to the lungs.
2. The left side pumps oxygen-rich blood to the body.
 In the lungs, blood picks up O2 and drops off CO2.
 In the body tissues, blood drops off O2 and picks up
CO2.
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22.10 Blood transports respiratory gases
 A mixture of gases, such as air, exerts pressure.
– Each kind of gas in a mixture accounts for a portion of the
total pressure of the mixture.
– Thus, each gas has a partial pressure.
– The exchange of gases between capillaries and the
surrounding cells is based on partial pressures.
– Molecules of each kind of gas diffuse down a gradient of
its own partial pressure, moving from regions of
– higher partial pressure to
– lower partial pressure.
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22.10 Blood transports respiratory gases
 Gases move from areas of higher concentration to
areas of lower concentration.
– Gases in the alveoli of the lungs have more O2 and less
CO2 than gases in the blood.
– O2 moves from the alveoli of the lungs into the blood.
– CO2 moves from the blood into the alveoli of the lungs.
– The tissues have more CO2 and less O2 than gases in the
blood.
– CO2 moves from the tissues into the blood.
– O2 moves from the blood into the tissues.
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22.10 Blood transports respiratory gases
Animation: CO2 from Blood to Lungs
Animation: CO2 from Tissues to Blood
Animation: O2 from Blood to Tissues
Animation: O2 from Lungs to Blood
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Figure 22.10
CO2 in exhaled air
O2 in inhaled air
Alveolar
epithelial
cells
Air spaces
CO2
O2
Alveolar
capillaries
of lung
CO2-rich,
O2-poor
blood
O2-rich,
CO2-poor
blood
Tissue
capillaries
CO2
Interstitial
fluid
Heart
O2
Tissue cells
throughout the body
Figure 22.10_1
Alveolar
capillaries
of lung
CO2-rich,
O2-poor
blood
O2-rich,
CO2-poor
blood
Tissue
capillaries
Heart
22.11 Hemoglobin carries O2, helps transport
CO2, and buffers the blood
 Most animals transport O2 bound to proteins called
respiratory pigments.
– Blue, copper-containing pigment is used by
– molluscs and
– arthropods.
– Red, iron-containing hemoglobin
– is used by almost all vertebrates and many invertebrates and
– transports oxygen, buffers blood, and transports CO2.
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Figure 22.11
Iron atom
O2 loaded
in lungs
O2 unloaded
in tissues
Heme group
Polypeptide chain
O2
O2
22.11 Hemoglobin carries O2, helps transport
CO2, and buffers the blood
 Most CO2 in the blood enters red blood cells.
 Some CO2 combines with hemoglobin.
 Other CO2 reacts with water, forming carbonic acid,
which then breaks apart into
– hydrogen ions and
– bicarbonate ions in a reversible reaction.
– Hemoglobin binds most of the H+ produced by this
reaction, minimizing the change in blood pH.
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22.11 Hemoglobin carries O2, helps transport
CO2, and buffers the blood
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22.12 CONNECTION: The human fetus
exchanges gases with the mother’s blood
 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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22.12 CONNECTION: The human fetus
exchanges gases with the mother’s blood
 Fetal hemoglobin
– attracts O2 more strongly than adult hemoglobin and
– takes oxygen from maternal blood.
 At birth
– CO2 in fetal blood increases and
– breathing control centers initiate breathing.
 Smoking during pregnancy reduces the supply of
oxygen to the fetus by up to 25%.
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Figure 22.12
Placenta, containing
maternal blood vessels
and fetal capillaries
Umbilical cord,
containing fetal
blood vessels
Amniotic
fluid
Uterus
You should now be able to
1. Describe the three main phases of gas exchange
in a human.
2. Describe four types of respiratory surfaces and
the kinds of animals that use them.
3. Explain how the amount of oxygen available in air
compares to that available in cold and warm fresh
water and cold and warm salt water.
4. Explain how the structure and movements of fish
gills maximize oxygen exchange.
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You should now be able to
5. Explain why breathing air is easier than using water
for gas exchange.
6. Describe the tracheal system of insects.
7. Describe the respiratory structures of the fossil
animal Tiktaalik.
8. Explain how the metabolic rate of a vertebrate
corresponds to the nature of its respiratory system.
9. Describe the structures and corresponding
functions of a mammalian respiratory system.
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You should now be able to
10. Describe the impact of smoking on human health.
11. Compare the mechanisms and efficiencies of lung
ventilation in humans and birds.
12. Explain how breathing is controlled in humans.
13. Explain how blood transports gases between the
lungs and tissues of the body.
14. Describe the functions of hemoglobin.
15. Explain how a human fetus obtains oxygen prior
to and immediately after birth.
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Figure 22.UN01
Lamella
Water flow
between
lamellae Blood
flow
Figure 22.UN02
Gas exchange
requires
moist, thin
often
relies on
(a)
(b)
for exchange of
to transport
gases between
red blood
cells contain
CO2
O2
(c)
needed waste
for product of
mammals and
(e)
ventilate by
(d)
binds and
transports
helps
to
(f)
tissue cells
regulated by
breathing control
center
transport CO2 and
buffer the blood
(g)
Figure 22.UN03
a.
b.
c.
d.
e.
f.
g.
h.
Figure 22.UN04
100
Llama
O2 saturation
of hemoglobin (%)
80
Human
60
40
20
0
0
20
40
60
PO
2
(mm Hg)
80
100