Download Chapter 34- Part 2 Respiratory

CAMPBELL BIOLOGY IN FOCUS
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
34
Circulation and
Gas Exchange
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
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Describe the function of the respiratory system.
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Concept 34.5: Gas exchange occurs across
specialized respiratory surfaces
 Gas exchange is the uptake of molecular O2 from
the environment and the discharge of CO2 to the
environment
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Gases hate to be in mixtures (e.g. gas mixtures,
dissolved in liquids, etc.).
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Partial Pressure Gradients in Gas Exchange
 Partial pressure is the pressure exerted by a
particular gas in a mixture of gases
 For example, the atmosphere is 21% O2, by volume,
so the partial pressure of O2 (PO2) is 0.21  the
atmospheric pressure
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 Partial pressures also apply to gases dissolved in
liquid, such as water
 When water is exposed to air, an equilibrium is
reached in which the partial pressure of each gas is
the same in the water and the air
 A gas always undergoes net diffusion from a region
of higher partial pressure to a region of lower partial
pressure
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There are 4 requirements a respiratory surface
must meet in order to be efficient at gas
exchange:
1. Moist
2. Thin membrane
3. Increased surface area
4. Connection to a circulatory system
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As we review the evolution and physiology of the
respiratory system, validate the claim made on
the last slide.
-Where is the respiratory surface?
-How does habitat affect the respiratory
structure?
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Respiratory Media
 O2 is plentiful in air, and breathing air is relatively
easy
 In a given volume, there is less O2 available in
water than in air
 Obtaining O2 from water requires greater energy
expenditure than air breathing
 Aquatic animals have a variety of adaptations to
improve efficiency in gas exchange
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Figure 34.17
Coelom
Gills
Parapodium (functions as gill)
(a) Marine worm
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Tube foot
(b) Sea star
Respiratory Surfaces
 Gas exchange across respiratory surfaces takes
place by diffusion
 Respiratory surfaces tend to be large and thin and
are always moist
 Respiratory surfaces vary by animal and can include
the skin, gills, tracheae, and lungs
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Gills in Aquatic Animals
 Gills are outfoldings of the body that create a large
surface area for gas exchange
 Ventilation is the movement of the respiratory
medium over the respiratory surface
 Ventilation maintains the necessary partial pressure
gradients of O2 and CO2 across the gills
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 Aquatic animals move through water or move water
over their gills for ventilation
 Fish gills use a countercurrent exchange system,
where blood flows in the opposite direction to water
passing over the gills
 Blood is always less saturated with O2 than the water
it meets
 Countercurrent exchange mechanisms are
remarkably efficient
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Figure 34.18
O2-poor blood
Gill
arch
Lamella
O2-rich blood
Blood
vessels
Gill arch
Water
Operculum
flow
Water flow
Blood flow
Countercurrent exchange
PO2 (mm Hg) in water
Gill filaments
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Net
diffusion
of O2
150 120 90 60
30
140 110 80 50
30
PO2 (mm Hg)
in blood
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Tracheal Systems in Insects
 The tracheal system of insects consists of a
network of air tubes that branch throughout the
body
 The tracheal system can transport O2 and CO2
without the participation of the animal’s open
circulatory system
 Larger insects must ventilate their tracheal system
to meet O2 demands
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Figure 34.19
Muscle fiber
2.5 m
Tracheoles Mitochondria
Tracheae
Air sacs
Body
cell
Tracheole
Air
sac
Trachea
External opening
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Air
Figure 34.19a
Muscle fiber
2.5 m
Tracheoles Mitochondria
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Lungs
 Lungs are an infolding of the body surface, usually
divided into numerous pockets
 The circulatory system (open and closed) transports
gases between the lungs and the rest of the body
 The use of lungs for gas exchange varies among
vertebrates that lack gills
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Considering the mammalian system, trace the
flow of air from the nasal orifice to the alveoli.
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Mammalian Respiratory Systems: A Closer Look
 A system of branching ducts conveys air to the lungs
 Air inhaled through the nostrils is warmed,
humidified, and sampled for odors
 The pharynx directs air to the lungs and food to the
stomach
 Swallowing tips the epiglottis over the glottis in the
pharynx to prevent food from entering the trachea
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 Air passes through the pharynx, larynx, trachea,
bronchi, and bronchioles to the alveoli, where gas
exchange occurs
 Exhaled air passes over the vocal cords in the
larynx to create sounds
 Cilia and mucus line the epithelium of the air ducts
and move particles up to the pharynx
 This “mucus escalator” cleans the respiratory
system and allows particles to be swallowed into the
esophagus
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 Gas exchange takes place in alveoli, air sacs at the
tips of bronchioles
 Oxygen diffuses through the moist film of the
epithelium and into capillaries
 Carbon dioxide diffuses from the capillaries across
the epithelium and into the air space
Animation: Gas Exchange
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Figure 34.20a
Nasal
cavity
Pharynx
Left
lung
Larynx
(Esophagus)
Trachea
Right lung
Bronchus
Bronchiole
Diaphragm
(Heart)
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Figure 34.20b
Branch of
pulmonary vein
(oxygen-rich
blood)
Branch of pulmonary
artery (oxygen-poor
blood)
Terminal
bronchiole
Alveoli
Capillaries
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Figure 34.20c
50 m
Dense capillary bed
enveloping alveoli (SEM)
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 Alveoli lack cilia and are susceptible to contamination
 Secretions called surfactants coat the surface of
the alveoli
 Preterm babies lack surfactant and are vulnerable to
respiratory distress syndrome; treatment is provided
by artificial surfactants
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Figure 34.21
Surface tension (dynes/cm)
Results
40
30
20
10
RDS deaths
0
Deaths from
other causes
(n  9)
(n  0)
<1,200 g
(n  29) (n  9)
>1,200 g
Body mass of infant
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Breathing is an example of
respiration, but not all respiration is
described as breathing!
Figure that one out…
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Concept 34.6: Breathing ventilates the lungs
 The process that ventilates the lungs is breathing,
the alternate inhalation and exhalation of air
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 An amphibian such as a frog ventilates its lungs by
positive pressure breathing, which forces air down
the trachea
 Birds have eight or nine air sacs that function as
bellows that keep air flowing through the lungs
 Air passes through the lungs of birds in one direction
only
 Passage of air through the entire system—lungs and
air sacs—requires two cycles in inhalation and
exhalation
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How a Mammal Breathes
 Mammals ventilate their lungs by negative
pressure breathing, which pulls air into the lungs
 Lung volume increases as the rib muscles and
diaphragm contract
 The tidal volume is the volume of air inhaled with
each breath
Animation: Gas Exchange
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Figure 34.22
Rib cage
expands as
rib muscles
contract.
Air
inhaled.
Rib cage gets
smaller as
rib muscles
relax.
Air
exhaled.
Lung
Diaphragm
1 Inhalation:
Diaphragm contracts
(moves down).
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2 Exhalation:
Diaphragm relaxes
(moves up).
 The maximum tidal volume is the vital capacity
 After exhalation, a residual volume of air remains
in the lungs
 Each inhalation mixes fresh air with oxygen-depleted
residual air
 As a result, the maximum PO2 in alveoli is
considerably less than in the atmosphere
***Making the inhalation of oxygen in air ALWAYS
favorable
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How long can you hold your breath?
Is it possible to hold it indefinitely?
Why?
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Control of Breathing in Humans
 In humans, the main breathing control center
consists of neural circuits in the medulla oblongata,
near the base of the brain
 The medulla regulates the rate and depth of
breathing in response to pH changes in the
cerebrospinal fluid
 The medulla adjusts breathing rate and depth to
match metabolic demands
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Figure 34.23-1
Homeostasis:
Blood pH of about 7.4
Stimulus:
Rising level of CO2
in tissues lowers
blood pH.
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Figure 34.23-2
Homeostasis:
Blood pH of about 7.4
Stimulus:
Rising level of CO2
in tissues lowers
blood pH.
Carotid
arteries
Sensor/control
center:
Cerebrospinal
fluid
Medulla
oblongata
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Aorta
Figure 34.23-3
Homeostasis:
Blood pH of about 7.4
Response:
Signals from
medulla to rib
muscles and
diaphragm
increase rate
and depth of
ventilation.
Stimulus:
Rising level of CO2
in tissues lowers
blood pH.
Carotid
arteries
Sensor/control
center:
Cerebrospinal
fluid
Medulla
oblongata
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Aorta
Figure 34.23-4
Homeostasis:
Blood pH of about 7.4
CO2 level
decreases.
Response:
Signals from
medulla to rib
muscles and
diaphragm
increase rate
and depth of
ventilation.
Stimulus:
Rising level of CO2
in tissues lowers
blood pH.
Carotid
arteries
Sensor/control
center:
Cerebrospinal
fluid
Medulla
oblongata
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Aorta
 Sensors in the aorta and carotid arteries monitor O2
and CO2 concentrations in the blood
 These sensors exert secondary control over
breathing
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Concept 34.7: Adaptations for gas exchange
include pigments that bind and transport gases
 The metabolic demands of many organisms
require that the blood transport large quantities
of O2 and CO2
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Coordination of Circulation and Gas Exchange
 Blood arriving in the lungs has a low PO2 and a high
PCO2 relative to air in the alveoli
 In the alveoli, O2 diffuses into the blood and CO2
diffuses into the air
 In tissue capillaries, partial pressure gradients favor
diffusion of O2 into the interstitial fluids and CO2 into
the blood
 Specialized carrier proteins play a vital role in this
process
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Animation: CO2 Blood to Lungs
Animation: CO2 Tissues to Blood
Animation: O2 Blood to Tissues
Animation: O2 Lungs to Blood
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Figure 34.24
120 27
Inhaled air
Exhaled air
160 0.2
O2 CO2
O2 CO2
Alveolar
epithelial
cells
CO2
O2
Alveolar
spaces
Alveolar
capillaries
Pulmonary
veins
Pulmonary
arteries
40 45
104 40
O2 CO2
O2 CO2
Systemic
veins
Systemic
arteries
Systemic
capillaries
Heart
CO2
O2
<40 >45
O2 CO2
Body tissue
cells
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Respiratory Pigments
 Respiratory pigments circulate in blood or
hemolymph and greatly increase the amount of
oxygen that is transported
 A variety of respiratory pigments have evolved
among animals
 These mainly consist of a metal bound to a protein
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 The respiratory pigment of almost all vertebrates
and many invertebrates is hemoglobin
 A single hemoglobin molecule can carry four
molecules of O2, one molecule for each ironcontaining heme group
 Hemoglobin binds oxygen reversibly, loading it in
the gills or lungs and releasing it in other parts of
the body
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Figure 34.UN01
Iron
Heme
Hemoglobin
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 Hemoglobin binds O2 cooperatively
 When O2 binds one subunit, the others change shape
slightly, resulting in their increased affinity for oxygen
 When one subunit releases O2, the others release
their bound O2 more readily
 Cooperativity can be demonstrated by the dissociation
curve for hemoglobin
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O2 saturation of hemoglobin (%)
Figure 34.25a
100
O2 unloaded
to tissues
at rest
80
O2 unloaded
to tissues
during exercise
60
40
20
0
0
20
Tissues during
exercise
40
60
Tissues
at rest
PO2 (mm Hg)
80
100
Lungs
(a) PO2 and hemoglobin dissociation
at pH 7.4
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 CO2 produced during cellular respiration lowers
blood pH and decreases the affinity of hemoglobin
for O2; this is called the Bohr shift
 Hemoglobin also assists in preventing harmful
changes in blood pH and plays a minor role in CO2
transport
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O2 saturation of hemoglobin (%)
Figure 34.25b
100
pH 7.4
80
pH 7.2
60
Hemoglobin
retains less
O2 at lower pH
(higher CO2
concentration
40
20
0
0
20
40
60
80
PO2 (mm Hg)
(b) pH and hemoglobin dissociation
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100
Carbon Dioxide Transport
 Most of the CO2 from respiring cells diffuses into the
blood and is transported in blood plasma, bound to
hemoglobin or as bicarbonate ions (HCO3–)
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Respiratory Adaptations of Diving Mammals
 Diving mammals have evolutionary adaptations that
allow them to perform extraordinary feats
 For example, Weddell seals in Antarctica can remain
underwater for 20 minutes to an hour
 For example, elephant seals can dive to 1,500 m and
remain underwater for 2 hours
 These animals have a high blood to body volume
ratio
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 Deep-diving air breathers can store large amounts
of O2
 Oxygen can be stored in their muscles in myoglobin
proteins
 Diving mammals also conserve oxygen by
 Changing their buoyancy to glide passively
 Decreasing blood supply to muscles
 Deriving ATP in muscles from fermentation once
oxygen is depleted
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