Transcript Chapter 22

MECHANISMS
OF GAS EXCHANGE
Copyright © 2009 Pearson Education, Inc.
Introduction: Surviving in Thin Air
 The process of gas exchange is 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 an animal with
lungs involves breathing, transport of gases,
and exchange of gases with tissue cells
 Three phases of gas exchange
– Breathing
– Transport of oxygen and carbon dioxide in blood
– 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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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
22.2 Animals exchange O2 and CO2 across moist
body surfaces
 Respiratory surfaces must be thin and moist for
diffusion of O2 and CO2
 Earthworms and other animals use their skin for gas
exchange
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Cut
Cross section
of 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
– Lungs in tetrapods that live on land
– Amphibians
– Reptiles
– Birds
– Mammals
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Body surface
Respiratory
surface
(gill)
CO2
O2
Capillary
Body surface
Respiratory
surface
(air tubes)
O2
CO2
Body cells
(no capillaries)
Body surface
CO2
CO2
O2
Respiratory
surface
(within lung)
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
– Increase the surface area for gas exchange
– Oxygen absorbed
– Carbon dioxide 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)
– Countercurrent flow of water and blood
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22.3 Gills are adapted for gas exchange in aquatic
environments
 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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Gill
arch
Gill
Oxygen-poor
blood
Direction
arch
of water
Direction
flow
Lamella
Oxygen-rich
blood
of water
flow
Gill
arch
Gill
Blood
vessels
arch
Blood
vessels
Operculum
Operculum
(gill cover)
Water flow
between
lamellae
(gill cover)
Gill
filaments
Blood flow
through
capillaries
in lamella
Countercurrent exchange
Water flow, showing % O2
Diffusion
of O2 from
water to
blood
Gill
15
filaments
100 70
40
80
30
60
5
Blood flow in
simplified capillary,
showing % O2
Oxygen-poor
blood
Lamella
Oxygen-rich
blood
Gill
arch
Blood
vessels
Water flow
between
lamellae
Gill
filaments
Blood flow
through
capillaries in
lamella
Countercurrent exchange
Water flow, showing % O2
100 70
Diffusion
of O2 from
water to
blood
80
40 15
60 30
5
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
– Air contains higher concentrations of O2
– Air is lighter and easier to move
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Air sacs
Tracheae
Opening
for air
Body
cell
Tracheole
Air
sac
Trachea
O2
CO2 Body wall
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 illustrates these air-breathing
adaptations
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22.5 EVOLUTION CONNECTION: The
evolution of lungs facilitated the movement
of tetrapods onto land
 The first tetrapods on land diverged into three
major lineages
– Amphibians use small lungs and their body surfaces
– Nonbird reptiles have lower metabolic rates and
simpler lungs
– Birds and mammals have higher metabolic rates and
more complex lungs
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22.6 In the human respiratory system, branching
tubes convey air to lungs located in the chest
cavity
 In mammals, air is inhaled through the nostrils
into the nasal cavity
– Air is filtered by hairs and mucus surfaces
– Air is warmed and moisturized
– Air is sampled for odors
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22.6 In the human respiratory system, 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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Oxygen-rich
blood
Nasal
cavity
Pharynx
Larynx
(Esophagus)
Oxygen-poor
blood
Bronchiole
Alveoli
Left lung
Trachea
Right lung
Bronchus
Blood
capillaries
Bronchiole
Diaphragm
(Heart)
22.6 In the human respiratory system, branching
tubes convey air to lungs located in the chest
cavity
 Alveoli are well adapted for gas exchange
– High surface area of capillaries
– High surface area of alveoli
 In alveoli
– O2 diffuses into the blood
– CO2 diffuses out of the blood
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22.7 CONNECTION: Smoking is a serious assault
on the respiratory system
 Mucus and cilia in the respiratory passages
– Protect the lungs
– Can be damaged by smoking
 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
– Heart disease
– 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
– Increases harmful types of cholesterol
 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
22.8 Negative pressure breathing ventilates our
lungs
 Breathing is the alternate inhalation and exhalation
of air (ventilation)
 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
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22.8 Negative pressure breathing ventilates our
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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Rib cage gets
Rib cage
expands as
rib muscles
contract
Air
inhaled
smaller as
rib muscles
relax
Air
exhaled
Lung
Diaphragm
Diaphragm contracts
(moves down)
Diaphragm relaxes
(moves up)
Inhalation
Exhalation
22.8 Negative pressure breathing ventilates our
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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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
TRANSPORT OF GASES
IN THE HUMAN BODY
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22.10 Blood transports respiratory gases
 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
 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
 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 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 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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Inhaled air
Exhaled air
Alveolar
epithelial
cells
Air spaces
CO2
O2
Alveolar
capillaries
CO2-rich,
O2-poor
blood
O2-rich,
CO2-poor
blood
Heart
Tissue
capillaries
CO2
Tissue cells
throughout
body
O2
Interstitial
fluid
22.11 Hemoglobin carries O2, helps transport CO2,
and buffers the blood
 Most animals transport O2 bound to proteins called
respiratory pigments
– Copper-containing pigment is used by
– Molluscs
– Arthropods
– Iron-containing hemoglobin
– Is used by almost all vertebrates and many invertebrates
– Transports oxygen, buffers blood, and transports CO2
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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 is transported as bicarbonate
ions in the plasma
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22.11 Hemoglobin carries O2, helps transport CO2,
and buffers the blood
CO2 + H2O
Carbon
Dioxide
Water
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H2CO3
Carbonic
Acid
H+ + HCO3Hydrogen
Ions
Bicarbonate
22.12 CONNECTION: The human fetus
exchanges gases with the mother’s
bloodstream
 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
bloodstream
 Fetal hemoglobin
– Attracts O2 more strongly than adult hemoglobin
– Thus, fetal blood takes oxygen from maternal blood
 At birth
– CO2 in fetal blood increases
– Breathing control centers initiate breathing
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Placenta, containing
maternal blood vessels
and fetal capillaries
Umbilical cord,
containing fetal
blood vessels
Amniotic
fluid
Uterus
Introduction: Surviving in Thin Air
 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?
– Geese have more efficient lungs than humans
– Geese hemoglobin has a very high affinity for oxygen
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100
Llama
80
Human
60
40
20
0
0
20
40
60
PO (mm Hg)
2
80
100
You should now be able to
1. Explain how geese can fly at altitudes higher
than Mount Everest
2. Describe the three main phases of gas exchange
in a human
3. Describe four types of respiratory surfaces and
the types of animals that use them
4. Explain how breathing air compares to using
water for gas exchange
Copyright © 2009 Pearson Education, Inc.
You should now be able to
5. Describe the parts and functions of the human
respiratory system
6. Describe the impact of smoking on human health
7. Explain how blood transports gases between the
lungs and tissues of the body
8. Describe the functions of hemoglobin
9. Explain how a fetus obtains oxygen before and
after birth
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Lamella
Water flow
Blood
flow
Gas exchange
requires
moist, thin
often
relies on
(b)
(a)
for exchange of
O2
to transport
gases between
red blood
cells contain
CO2
(c)
(d)
needed
waste
for
product of
mammals
ventilate by
(e)
binds and
transports
and
helps
to
(f)
tissue cells
regulated by
breathing control
centers
transport CO2 and
buffer the blood
(g)
a.
b.
c.
d.
e.
f.
g.
h.