Transcript Chapter 22

Chapter 22
Gas Exchange
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Surviving in Thin Air
• The air at the height of Mt. Everest is so low in
oxygen that most people would pass out
instantly if exposed to it
• Geese that migrate over high mountains have
adaptations for using and storing oxygen
efficiently
• Humans living at extremely high altitudes have
adapted to function with relatively little oxygen
• Gas exchange is the interchange of O2 and the
waste product CO2 between an animal and its
environment
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
MECHANISMS OF GAS EXCHANGE
22.1 Overview: Gas exchange involves breathing,
transport of gases, and exchange of gases with tissue
cells
• Gas exchange provides O2 for cellular
respiration and removes its waste product,
CO2
– Involves respiratory and circulatory systems
• Gas exchange has three phases
1. Breathing
• O2 is taken into lungs and blood
vessels
• CO2 diffuses out and leaves body
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2. Transport of gases by the circulatory system
• O2 attaches to hemoglobin and is carried
in blood to body tissues
• CO2 is transported from tissues back to
lungs
3. Body cells take up O2 from blood and
release CO2 back to the blood
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-1
O2
Breathing
CO2
Lung
Circulatory
system
Transport
of gases by
the circulatory
system
Mitochondria
Exchange of
gases with
body cells
O2
CO2
Capillary
Cell
22.2 Animals exchange O2 and CO2 across moist
body surfaces
• For diffusion of O2 and CO2 to occur in both
aquatic and terrestrial animals
– Respiratory surfaces must be thin and moist
– Gases must be dissolved in water
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• Gas exchange occurs in four types of
respiratory organs
– Entire outer skin: animals living in moist
environments
– Gills: most aquatic animals
– Tracheal system: insects
– Lungs: most terrestrial vertebrates
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LE 22-2a
Cut
Cross section
of respiratory
surface (the
skin covering
the body)
CO2
O2
Capillaries
LE 22-2b
Body surface
Respiratory
surface
(gill)
CO2
O2
Capillary
LE 22-2c
Body surface
O2
CO2
Body cells
(no capillaries)
Respiratory
surface
(air tubes)
LE 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 that absorb O2
dissolved in water
– Found in fishes and many invertebrates
– Are among the most efficient gas exchange
organs in the aquatic world
• Ventilation increases the flow of the
surrounding water over the respiratory surface
– Requires considerable energy from fish
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Arrangement of capillaries in a fish gill
enhances gas exchange
– Blood flows in a direction opposite to water
flow
– Countercurrent exchange
• Transfers something from a fluid moving in
one direction to another fluid moving in the
opposite direction
• Enables gills to remove more than 80% of
the O2 in the water flowing past them
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-3
Gill arch
Oxygen-poor
blood
Direction
of water
flow
Lamella
Oxygen-rich
blood
Gill arch
O2
Blood
vessels
% O2 in water
flowing over
lamellae
% O2 in blood flowing
through capillaries
in lamellae
Gill
filaments
Countercurrent exchange
22.4 The tracheal system of insects provides
direct exchange between the air and body cells
• Advantages to exchanging gases by breathing
air
– Air contains a high concentration of O2
– Air is lighter and easier to move than water
• Main problem with breathing air: loss of water
to air by evaporation
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• Tracheal systems in insects
– Transport O2 directly to cells through a
network of finely branched tubes throughout
the body
– In small insects, diffusion is sufficient to
exchange gases
– Large insects may ventilate the tracheal
system with rhythmic body movements
– In many insects, contraction and relaxation
of flight muscles pumps air through the
tracheal system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-4a
Air sacs
Tracheae
Opening
for air
Body
cell
Air
sac
Tracheole
Trachea
O2
CO2
Body wall
22.5 Terrestrial vertebrates have lungs
• Amphibians have small lungs and rely heavily
on diffusion of gases across body surfaces
• Most reptiles (including birds) and mammals
rely exclusively on lungs
– Size and complexity of lungs are correlated
with metabolic rate
– Lungs are restricted to one location in the
body
• Circulatory system must transport gases
between lungs and rest of body
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• Pathway of air in mammals
– Inhaled through the nostrils
– Passes through the pharynx and larynx
(including vocal cords)
– Into the trachea, bronchi, and bronchioles
• Bronchioles end in clusters of tiny
alveoli,where gas exchange occurs
• Cilia and mucus are the respiratory system's
cleaning elements
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LE 22-5b
Oxygen-rich
blood
Oxygen-poor
blood
Bronchiole
Alveoli
Blood
capillaries
CONNECTION
22.6 Smoking is a deadly assault on our
respiratory system
• Tobacco smoke irritates cells lining the bronchi
– Inhibits or destroys cilia
– Kills defensive macrophages
• Smoking causes lung cancer, emphysema,
and cardiovascular disease
• Choosing not to smoke is the most important
lifestyle choice for health
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LE 22-6
Lung
Heart
22.7 Breathing ventilates the lungs
• Breathing is the alternation of inhalation and
exhalation
– Maintains high O2 and low CO2 at the
respiratory surface
• Negative pressure breathing
– During inhalation, changes in lungs,
diaphragm, and rib cage reduce air
pressure in alveoli
– Air rushes in due to higher pressure outside
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– During exhalation, decreased volume of
chest cavity forces air out
– Vital capacity is the maximum volume of air
we can inhale and exhale during forced
breathing
– A residual volume of air ("dead air") remains
in lungs even after exhalation
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LE 22-7a
Rib cage
expands as
rib muscles
contract
Air
inhaled
Rib cage gets
smaller as
rib muscles
relax
Air
exhaled
Lung
Diaphragm
Diaphragm contracts
(moves down)
Diaphragm relaxes
(moves up)
Inhalation
Exhalation
• Birds have a one-way flow of air through the
lungs
– Several large sacs act as bellows to keep
air flowing
– Tiny parallel tubes, not alveoli, function in
gas exchange
– No residual volume, so lung oxygen
concentrations are higher in birds than in
humans
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-7b
Air
Air
Anterior
air sacs
Trachea
Posterior
air sacs
Lungs
Air
tubes
in lung
SEM 9
Inhalation:
Air sacs fill
Exhalation:
Air sacs empty; lungs fill
22.8 Breathing is automatically controlled
• Breathing control centers in the brain signal
diaphragm and rib muscles to contract about
10-14 times a minute
• Control centers adjust breathing rate to
respond to body's needs by monitoring CO2
level in the blood
– High CO2 results in a drop in blood pH
– Low pH triggers an increase in the rate and
depth of breathing, bringing in more O2
– Response to O2 level is thus indirect
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• Hyperventilation purges blood of so much CO2
that control centers cease to send signals and
breathing stops
• Secondary control over breathing is exerted by
sensors in the aorta and carotid arteries
– Monitor concentrations of O2 and CO2
– Signal control centers in brain to increase
rate of breathing when O2 is low
• Breathing rate must be coordinated with
activity of the circulatory system
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-8-2
Brain
Cerebrospinal
fluid
Pons
Breathing control centers
stimulated by:
Medulla
CO2 increase/pH decrease
in blood
Nerve signals indicating
CO2 and O2 levels
Nerve signals
trigger
contraction
of muscles
Diaphragm
Rib muscles
CO2 and O2
sensors
in aorta
TRANSPORT OF GASES IN THE BODY
22.9 Blood transports respiratory gases
•
One side of the heart pumps O2-poor, CO2-rich blood
from the body to the lungs
•
The other side of the heart pumps O2-rich, CO2-poor
blood from the lungs to the rest of the body
•
Gases are exchanged between capillaries and cells
– Each kind of gas accounts for a partial pressure of
the air mixture
– Molecules of each kind of gas diffuse down a
gradient of the gas's partial pressure, independent
of other gases
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-9
Exhaled air
Alveolar
epithelial
cells
Inhaled air
Air spaces
CO2
O2
Alveolar
capillaries of
lung
O2-rich,
CO2-poor
blood
CO2-rich,
O2-poor
blood
Heart
Tissue
capillaries
CO2 Interstitial O2
fluid
Tissue cells
throughout body
22.10 Hemoglobin carries O2 and helps transport
CO2 and buffer the blood
• Most of the O2 in blood is carried by
hemoglobin in red blood cells
• Each hemoglobin molecule can carry up to
four oxygen molecules
– Loads up with O2 in lungs, transports it to
tissues, unloads some or all depending on
needs of cells
• Hemoglobin also helps blood transport CO2
and assists in preventing harmful changes in
pH
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-10
Iron atom
O2 loaded
in lungs
O2 unloaded
in tissues
Heme group
Polypeptide chain
O2
O2
Animation: O2 From Blood to Tissues
Animation: CO2 From Tissues to Blood
Animation: CO2 From Blood to Lungs
Animation: O2 From Lungs to Blood
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CONNECTION
22.11 The human fetus exchanges gases with
the mother's bloodstream
• A human fetus exchanges gases with the
outside world through the placenta
– Fetal capillaries exchange gases with
maternal blood that circulates in the
placenta
– Maternal circulatory system carries the
gases to and from the mother's lungs
– O2 uptake is aided by fetal hemoglobin,
which attracts O2 strongly
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• When a baby is born, CO2 stops diffusing from
the fetus into the placenta
– Increased blood CO2 stimulates the infant's
breathing control centers to initiate
breathing
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 22-11
Placenta, containing
maternal blood vessels
and fetal capillaries
Umbilical cord,
containing fetal
blood vessels
Amniotic
fluid
Uterus