copyright © 2009 pearson education, inc. mechanisms of gas exchange
TRANSCRIPT
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Copyright © 2009 Pearson Education, Inc.
MECHANISMS OF GAS EXCHANGE
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The process of gas exchange is called respiration, the interchange of
– O2 and the waste product CO2
– Between an organism and its environment
Introduction: Surviving in Thin Air
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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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Lung
Exchangeof gaseswithbodycells
Cell
Capillary
Mitochondria
Breathing
Circulatorysystem
Transportof gases bythe circulatorysystem
CO2
CO2
O2
O21
2
3
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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
CO2
O2
Cross sectionof respiratorysurface (theouter skin)
Capillaries
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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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CO2
O2
Capillary
Body surface
Respiratorysurface(gill)
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CO2
O2
Body surface
Body cells(no capillaries)
Respiratorysurface(air tubes)
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CO2 O2
Body surface
Capillary
Respiratorysurface(within lung)
O2CO2
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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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Gillarch
Directionof waterflow
Operculum(gill cover)
Gillarch
Bloodvessels
Oxygen-richblood
Oxygen-poorblood
Lamella
Gillfilaments
Water flowbetweenlamellae
Blood flowthroughcapillariesin lamella
Countercurrent exchange
Blood flow insimplified capillary,
showing % O2
Diffusionof O2 fromwater toblood
Water flow, showing % O2
100 70 40 15
5306080
Gillarch
Directionof waterflow
Operculum(gill cover)
Gillarch
Bloodvessels
Gillfilaments
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Gillarch
Bloodvessels
Oxygen-richblood
Oxygen-poorblood
Lamella
Gillfilaments
Water flowbetweenlamellae
Blood flowthroughcapillaries inlamella
Countercurrent exchange
Blood flow insimplified capillary,
showing % O2
Diffusionof O2 from
water toblood
Water flow, showing % O2
100 70 40 15
5306080
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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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TracheaeAir sacs
Openingfor air
Bodycell
TracheoleAirsac
Trachea
Body wallCO2O2
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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-richblood
Bronchiole
Alveoli
Oxygen-poorblood
Bloodcapillaries
Nasalcavity
Left lung
Pharynx
Larynx
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
(Heart)
(Esophagus)
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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
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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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Lung
Diaphragm contracts(moves down)
Diaphragm relaxes(moves up)
Diaphragm
Inhalation Exhalation
Airinhaled
Airexhaled
Rib cageexpands asrib musclescontract
Rib cage getssmaller asrib musclesrelax
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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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Cerebrospinalfluid
Pons
Medulla
Brain
Nerve signalstrigger contractionof muscles
Diaphragm
Rib muscles
1
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Cerebrospinalfluid
Pons
Medulla
Brain
Nerve signalstrigger contractionof muscles
Diaphragm
Rib muscles
1
Breathing controlcenters respondto pH of blood
2
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Cerebrospinalfluid
Pons
Medulla
Brain
Nerve signalstrigger contractionof muscles
Diaphragm
Rib muscles
1
Breathing controlcenters respondto pH of blood
2
Nerve signalsindicating CO2
and O2 levels
3
CO2 and O2
sensors in aorta
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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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Alveolarepithelialcells
CO2 O2
CO2-rich,O2-poorblood
O2-rich,CO2-poorblood
Exhaled air Inhaled air
Air spaces
Alveolarcapillaries
Tissuecapillaries
Tissue cellsthroughoutbody
Interstitialfluid
Heart
CO2 O2
CO
2 O 2
O2CO 2
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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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O2 loadedin lungs
O2 unloadedin tissues
Iron atom
Polypeptide chainHeme group
O2
O2
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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
+ - 2 2 2 3 3Carbon Water Carbonic Hydrogen Bicarbonate Dioxide Acid Ions
CO + H O H CO H + HCO
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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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Amnioticfluid
Uterus
Umbilical cord,containing fetalblood vessels
Placenta, containingmaternal blood vesselsand fetal capillaries
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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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P
Llama
Human
00
20
20
40
40 60
60
80
80 100
100
O2(mm Hg)
O2
satu
rati
on
of
hem
og
lob
in (
%)
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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
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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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Bloodflow
Water flow
Lamella
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transport CO2 andbuffer the blood
tissue cells
regulated by
breathing controlcenters
mammalsventilate by
helpsto
and binds andtransports
to transportgases between
red bloodcells contain
Gas exchange
requiresmoist, thin
oftenrelies on
for exchange of
neededfor
wasteproduct of
CO2O2
(e)
(d)(c)
(b)(a)
(g)(f)
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a.
b.c.d.
e.
g.
f.
h.