Transcript Chapter 42 Respiration

Circulation and Gas
Exchange
Chapter 42
A.P. Biology
Mr. Knowles
Liberty Senior High
It’s all because of cellular
respiration!
C6H12O6 + 6O2 --> 6CO2 + 6H2O
+
And
(ATP)
Eliminate
This!
We Need This!
To Make This!
• Concept 42.5: Gas exchange occurs across specialized
respiratory surfaces
• Gas exchange supplies oxygen for cellular respiration
and disposes of carbon dioxide.
Respiratory
medium
(air of water)
O2
CO2
Respiratory
surface
Organismal
level
Circulatory system
Cellular level
Energy-rich
molecules
from food
Figure 42.19
Cellular respiration
ATP
• Animals require large, moist
respiratory surfaces for the adequate
diffusion of respiratory gases:
– Between their cells and the
respiratory medium, either air or
water.
• Overview: Trading with the
Environment
• Every organism must exchange
materials with its environment
–And this exchange ultimately
occurs at the cellular level
• In unicellular organisms:
–These exchanges occur directly
with the environment.
• For most of the cells making up
multicellular organisms:
–Direct exchange with the
environment is not possible.
• Concept 42.1: Circulatory
systems reflect phylogeny
• Transport systems
– Functionally connect the
organs of exchange with the
body cells.
• Most complex animals have internal
transport systems:
– That circulate fluid, providing a lifeline
between the aqueous environment of
living cells and the exchange organs,
such as lungs, that exchange chemicals
with the outside environment
External Respiration
• Uptake of O2 and the release of CO2 into the
environment- external respiration.
• Dry Air = 78 % N2, 21 % O2 , 0.93% argon
and other inert gases, and 0.03 % CO2 .
• Amount of air changes at altitude, but not
composition.
• Each gas exerts a fraction of total
atmospheric pressure- partial pressure (PN2,
PO2, PCO2…)
Remember the Plasma
Membrane?
• Like H2O, O2 and CO2 diffuse through
the phospholipid bilayer.
• Membrane must have H2O on both
sides for its integrity (hydrophobic).
• All terrestrial organisms obtain gas
diffusion across a moist membrane,
never dry. Dissolved gases (O2 and
CO2 ) diffuse through.
Intracellular Diffusion of
Gases is Passive
[CO2] is lower
Aerobically
Respiring Cell
[CO2] is higher
[O2] is lower
[O2] is higher
Dissolved Oxygen in Water
• Factors that affect O2 solubility in
H2O:
1. PO2 in air, decreases with altitude.
Less PO2 , less dissolved O2 in the
H2O.
2. Temperature of the H2O. Inversely
related.
3. Concentration of other solutes in
H2O. Inversely related.
What happens to the
oxygen level when tides
go out?
The Story of the Tarpon
Discovery: Blue PlanetTidal Seas
Problems in External Respiration
• Simple diffusion- limited to a
distance of 0.5 mm.
• As organisms become larger, their
surface area to volume ratio
decreases.
• Keep Intracellular [O2] <
Extracellular [O2]. If not, there is no
net movement of O2 by diffusion.
Invertebrate Circulation
• The wide range of invertebrate
body size and form:
–Is paralleled by a great diversity
in circulatory systems
Evolution of External Respiration
• Unicellular bacteria and protists –
simple diffusion.
Problem: Limits size of organism.
• Jellyfish (Phylum Cnidaria)– have
no respiratory system. Very thin
and slow down metabolism to
allow diffusion of gases. (an
unusual case)
Gastrovascular Cavities
• Simple animals, such as cnidarians
– Have a body wall only two cells thick that encloses a
gastrovascular cavity.
• The gastrovascular cavity
– Functions in both digestion and distribution of
substances throughout the body.
• Some cnidarians, such as jellies:
– Have elaborate gastrovascular cavities
Circular
canal
Radial canal
Mouth
5 cm
Figure 42.2
The Jellyfish Life!
Discover: Blue PlanetSeasonal Seas
Cyanea capillata – 7 ft. bell, 120 ft
tentacles
Creating a Water Current
• Sponges (Phylum Porifera)
– diffusion directly from
surrounding water; set up a
current using cilia. Beating
cilia replace water over the
diffusion surface.
Sponges (Porifera)
Sponges (Porifera)
Sponges and Corals
Discovery: Blue PlanetCoral Seas
Creating a Water Current
• Problem: Limited to aquatic
environments; not efficient for
really large organisms.
But sponges are aquatic!
What about terrestrial
organisms?
Enter Cutaneous
Respiration!
Cutaneous Respiration
• Cutaneous Respiration – gas
exchange occurs directly across
an animal’s body surface.
• Problem: Must stay moist for
gas diffusion; must increase
body surface area; limits size.
The Worms!
• Flatworms (Phylum Platyhelminthes)
– very thin to permit direct diffusion
from surrounding fluid (tapewormshost fluid).
• Roundworms (Phylum Nematoda)
and Earthworms (Phylum Annelida)
- direct diffusion; requires a moist
cuticle; often secret mucous to keep
skin wet.
• Many segmented worms have flaplike gills
– That extend from each segment of their body.
(b) Marine worm. Many
polychaetes (marine
worms of the phylum
Annelida) have a pair
of flattened appendages
called parapodia on
each body segment. The
parapodia serve as gills
and also function in
crawling and swimming.
Parapodia
Gill
Figure 42.20b
So why do earthworms
die on your driveway
after a rain?
They dry out and, therefore,
suffocate!
Mouth-to-skin, anyone?
What are the down sides
to cutaneous respiration?
The World’s Largest Earthworm
Video: Nigel Marvin’s Giant
Creepy Crawlies
Scolex
Proglottids
Cutaneous Respiration in
a Tapeworm
Video: The Body
Snatchers
Increasing the Diffusion
Surface Area
• Advanced Invertebrates (Phylum
Echinodermata, Mollusca,
Arthropoda) – increase surface area
and bring external fluid close to
internal fluid.
• Use a primitive gill - increases
diffusion surface area.
• In some invertebrates
(
– The gills have a simple shape and are distributed
over
much
of
the
body
a) Sea star. The gills of a sea
star are simple tubular
projections of the skin.
The hollow core of each gill
is an extension of the coelom
(body cavity). Gas exchange
occurs by diffusion across the
gill surfaces, and fluid in the
coelom circulates in and out of
the gills, aiding gas transport.
The surfaces of a sea star’s
tube feet also function in
gas exchange.
Gills
Coelom
Figure 42.20a
Tube foot
Primitive Gill
• Phylum Echinodermata – use a
primitive gill called papulae.
papula
O2
CO2
Epidermis
Body Cavity
• The gills of clams, crayfish, and many other
animals:
– Are restricted to a local body region.
(d) Crayfish. Crayfish and
other crustaceans
have long, feathery
gills covered by the
exoskeleton. Specialized
body appendages
drive water over
the gill surfaces.
(c) Scallop. The gills of a
scallop are long,
flattened plates
that project from the
main body mass
inside the hard shell.
Cilia on the gills
circulate water around
the gill surfaces.
Gills
Gills
Figure 42.20c, d
Axolotl- permanent
salamander larvae
External Gills
CO2
O2
The External Gills
• Some, like the axolotl (aquatic
salamander) physically moves its
external gills through the water for
improved gas exchange.
• A problem with external gills: Difficult
to circulate water past surfaces
constantly.
• Problem: external gills are fragile and
offer resistance in water.
Brachial Chambers
• Brachial chambers – a muscular,
internal pouch used to pump water
over the gills.
• Phylum Mollusca – use an internal
mantle cavity that pumps water
over gills. Ex. Squid and octopi.
Internal Gills
• Cartilaginous Fishes (Sharks
and Rays) – force water through
mouth over internal gills by
constant swimming. Water flows
out gill slits.
• Swim with mouth open to force
water over gills – ram ventilation.
• Problem: Must stay in motion or
suffocate.
Filament
• The feathery gills projecting from a salmon
– Are an example of a specialized exchange
system found in animals.
Figure 42.1
The Best Brachial Chamber
• Bony Fishes – have opercular cavities.
Gills are between mouth and opercular
cavities.
• Opercula (Gill Covers) – are flexible
and they pull water through cavity, like a
bellows.
• Each gill – two rows of gill filaments and
each filament has rows of lamellae
parallel to direction of water movement
(see Fig. 46.6).
• The effectiveness of gas exchange in some gills,
including those of fishes:
– Is increased by ventilation and countercurrent flow of
blood and water.
Oxygen-poor
blood
Gill arch
Oxygen-rich
blood
Lamella
Blood
vessel
Gill
arch
Water
flow
Operculum
O2
Water flow
over lamellae
showing % O2
Figure 42.21
Gill
filaments
Blood flow
through capillaries
in lamellae
showing % O2
Countercurrent exchange
The Gill Filament
• In each lamella, blood flows in a
direction opposite the direction of water
movement – countercurrent flow.
• Maximizes the differences in O2
between the water and blood (see Fig.
46.7).
• Most efficient respiratory organ
known – 85% available oxygen is
removed.
Countercurrent Flow in Gills
What if you’re not aquatic?
Why do fish die out of
water?
They suffocate.
The Problem of Terrestrial
Respiration
• Water – 5-10 ml of O2 per liter
• Air – 210 ml O2 per liter (rich in O2)
• Gills don’t work in air :
– Air is less buoyant than water, fragile
lamellae collapse and reduce surface area
and not enough gas diffusion.
– Water diffuses into air by evaporation.
Gills provide too much surface area for
water loss.
Terrestrial Organisms
• Use two types of internal passage ways for
gas diffusion; sacrifice efficiency for reduced
evaporation.
• Terrestrial Insects use tracheae – air-filled
passages connecting the surface of the insect
to all potions of its body. Diffusion directly
with internal cells and no circulatory
system.
• Use openings called spiracles along the
abdomen that can be controlled. Effective
for small animals.
Tracheal Systems in Insects
• The tracheal system of insects
– Consists of tiny branching tubes that penetrate the body
Air sacs
Tracheae
Spiracle
(a) The respiratory system of an insect consists of branched internal
tubes that deliver air directly to body cells. Rings of chitin reinforce
the largest tubes, called tracheae, keeping them from collapsing.
Enlarged portions of tracheae form air sacs near organs that require
a large supply of oxygen. Air enters the tracheae through openings
called spiracles on the insect’s body surface and passes into smaller
tubes called tracheoles. The tracheoles are closed and contain fluid
(blue-gray). When the animal is active and is using more O2, most of
the fluid is withdrawn into the body. This increases the surface area
of air in contact with cells.
Figure 42.22a
• The tracheal tubes
– Supply O2 directly to body cells.
Body
cell
Tracheole
Air
sac
Trachea
Tracheoles
(b) This micrograph shows cross
sections of tracheoles in a tiny
piece of insect flight muscle (TEM).
Each of the numerous mitochondria
in the muscle cells lies within about
5 µm of a tracheole.
Figure 42.22b
Body wall
Air
Mitochondria
Myofibrils
2.5 µm
How large can an insect
become?
Video: Nigel Marvin’s
Giant Creepy Crawlies
First Terrestrial Organism
• Problem: Tracheal breathing
limits the size of the organism.
Ventilation is by movement of
organism.
Lungs
• Spiders, land snails, and most
terrestrial vertebrates:
– Have internal lungs (simple sacs).
Other Terrestrial Organ
• Lung – moves air through a moist,
internal, tubular passage and back
out same passage.
• Benefit – minimizes evaporation.
• Problem: lower efficiency than gill,
but O2 more abundant in air.
• Four variations of the terrestrial,
vertebrate lung.
The First Terrestrial Animals?
Class Amphibia
• Amphibian Lung – simple sac with a
folded membrane; has trachea with a
valve – glottis.
• Can breathe through nose and mouth.
• Perform positive pressure breathing –
create a positive pressure outside and
forces air into lungs (throat breathing
in frogs).
I
supplement
by lung
breathing
with
cutaneous
respiration,
too!
Problems with the Amphibian
System
• Lung is not very efficient; poor surface
area.
• Cutaneous Respiration – requires moist
skin. Limited to moist environments
and/or secrete mucous covering.
Dependent on water.
• Cannot be very active; slower
metabolism.
Class Reptilia
• Living completely on land, no
connection to water. Made watertight skin (scales) to prevent
evaporation.
• Little or no cutaneous respiration.
• Reptile Lung – contains many
small air chambers; increase
surface area.
Class Reptilia
• Reptiles use negative pressure
breathing – intercostal muscles and
diaphragm to expand thoracic cavity
and create a negative pressure in
lungs.
• Air is pulled into lungs rather than
pushed.
• Also called body cavity breathing
or chest breathing.
Class Mammalia
• Must maintain constant body temperature –
need more efficient lung.
• Use millions of sacs, clustered like grapes –
alveoli (alveolus = sing.)
• Each cluster connected to a short, branching
passageway – bronchiole.
• Bronchioles connect into left and right
bronchi (bronchus = sing.)
• Bronchi are connected to superior trachea.
How a Mammal Breathes
• Mammals ventilate their lungs
– By negative pressure breathing, which pulls air into the
lungs.
Rib cage
expands as
rib muscles
contract
Air inhaled
Rib cage gets
smaller as
rib muscles
relax
Air exhaled
Lung
Diaphragm
INHALATION
Diaphragm contracts
(moves down)
Figure 42.24
EXHALATION
Diaphragm relaxes
(moves up)
Bronchioles
Bronchi
(No Cartilage)
Oxygenated Blood
Deoxygenated Blood
About 1 µm
80
2
m
of Surface Area!
Mechanics of Human Breathing
• Trachea and Bronchi have hyaline cartilage,
but not bronchioles.
• Bronchioles are surrounded by smooth
muscle.
• Bronchoconstriction – nervous system or
hormones (histamine) signal smooth muscle
to contract and narrow bronchioles (asthma).
• Bronchodilation - nervous system or
hormones (epinephrine) signal smooth
muscle to relax and open bronchioles.
Mechanics of Human
Breathing
• Visceral Pleural Membrane –
surrounds outside of lung.
• Parietal Pleural Membrane – lines
thoracic cavity.
• Pleural Cavity – is fluid-filled space
between; connects lung to wall of
cavity.
Mechanics of Human Breathing
• One-cycle pump.
• Inspiration: intercostal muscles and
diaphragm contract = increase volume of
thoracic cavity.
• Pleural membranes are coupled, lungs
expand.
• Air pressure in lungs is decreased and air
is pulled in – negative pressure
breathing.
Mechanics of Human Breathing
• One-cycle pump.
• Expiration: Intercostal muscles and
diaphragm relax, elastic recoil of
thoracic cavity = decrease volume
of cavity and lungs.
• Air pressure in lungs is increased,
forces air out.
Mechanics of Human Breathing
• Tidal Volume = amount of air
moved into and out of lungs at rest
(500 ml).
• Functional Residual Capacity =
amount of air left in lungs after
normal expiration at rest.
• Residual Volume = amount of air
left after forceful, maximum
expiration.
Mechanics of Human Breathing
• Anatomical Dead Space = constant
amount of air trapped in trachea,
bronchi, bronchioles (150 ml).
• Vital Capacity = max. amount of air
exhaled after a forceful, maximum
inhalation (VC = TV + IRV + ERV).
• Total Lung Capacity = TV + IRV +
ERV + RV
Class Aves
• Flight requires more ATP.
• Avian lung is a two-cycle pump
(Fig. 46-9).
• Uses a system of anterior and
posterior air sacs and a lung.
• Gas exchange occurs in lung only.
How a Bird Breathes
• Besides lungs, bird have eight or nine air sacs
– That function as bellows that keep air flowing through
the lungs.
Air
Air
Anterior
air sacs
Trachea
Posterior
air sacs
Lungs
Lungs
Air tubes
(parabronchi)
in lung
INHALATION
Air sacs fill
EXHALATION
Air sacs empty; lungs fill
Figure 42.25
1 mm
5
3
2
1
4
Two-Cycle Breathing
• 1st Inspiration – air travels down
trachea to posterior air sacs.
• 1st Expiration – air flows from sacs to
lung.
• Lung – gas exchange.
• 2nd Inspiration – air flows from lung to
anterior air sacs.
• 2nd Exhalation – air flows from sacs out
through trachea.
Benefits to Avian Breathing
• Unidirectional flow of air through lung
– no “dead volume” of air left in lung.
Always fully oxygenated air.
• Flow of blood is perpendicular to air
flow – cross-current flow.
• Very efficient at extracting oxygen from
air.
• Most efficient terrestrial respiration.
Gas Transport and Exchange
• If transport were by simple diffusion,
then O2 would require three years to
travel from lung to toe.
• Use a circulatory system; but plasma
could only carry 3 ml O2 per l.
• Use RBC with hemoglobin to carry
200 ml O2 per l.
Erythrocyte
Hemoglobin (Hb)
• Accounts for 95% of proteins
inside the RBC.
• 280 million Hbs in each RBC.
• Hb binds to and transports O2 and
CO2.
Hb Molecule
• Each Hb molecule = four protein chains
= 2 alpha chains + 2 beta chains of
polypeptides.
• Each chain is a globular subunit and has a
heme group.
• Heme – a porphyrin which is a ring
compound with an iron in the center.
• Iron has a + charge and can bind to O2
(negative).
• Like all respiratory pigments:
– Hemoglobin must reversibly bind O2, loading
O2 in the lungs and unloading it in other parts
of the body
Heme group
Iron atom
O2 loaded
in lungs
O2 unloaded
In tissues
Figure 42.28
Polypeptide chain
O2
O2
Quaternary Structure of
Hemoglobin
Hb Molecule
• When hemoglobin binds to O2 – it
becomes oxyhemoglobin (bright red).
• Very weak interaction; easy to
separate.
• At the tissues, some oxyhemoglobin
releases its O2 becomesdeoxyhemoglobin (dark red).
Oxygenated Blood
PO2 = 105 mm Hg
PO2 = 100 mm Hg
Deoxygenated Blood
Oxygen Transport
• Lungs are efficient; 97 % of hemoglobin
in RBC’s is fully saturated.
• At capillaries, extracellular fluid has
lower PO2 and O2 diffuses into tissues.
• Venous blood leaving tissues has PO2 = 40
mm Hg.
• Only about 22% of oxyhemoglobin has
releases O2 into tissues.
[O2] is higher
Body Tissues
[O2] is lower
Inhaled air
160
O2
Alveolar
epithelial
cells
Exhaled air
0.2
CO2
Blood
entering
alveolar
capillaries
104 40
O2
CO2
O2
CO2
2
1
O2
Alveolar
capillaries
of lung
40 45
O2
CO2
Pulmonary
arteries
Systemic
veins
Blood
leaving
tissue
capillaries
40
O2
Figure 42.27
45
CO2
120 27
O2 CO2
Alveolar spaces
104
O2
40
CO2
Pulmonary
veins
Systemic
arteries
Heart
Tissue
3
capillaries
4 2
CO
Blood
leaving
alveolar
capillaries
O2
Blood
entering
tissue
capillaries
O2
CO2
Tissue
cells
<40 >45
O2
CO2
100
O2
40
CO2
Why so little O2 released into
tissues?
• Blood can supply oxygen needs
during exercise.
• Blood has enough oxygen to
maintain life 4 or 5 minutes
without breathing.
How does Hb “know” when to
let go?
• In RBC, CO2 + H2O
H2CO3 , lowers
pH.
• Hb’s affinity for O2 decreases with
lower pH. Releases oxygen into tissue.
• Hb’s affinity for O2 inversely related
to temperature. Metabolically active
tissues are warmer. Cause release of O2
into tissues.
1
2
Carbon dioxide produced by
body tissues diffuses into the
interstitial fluid and the plasma.
Over 90% of the CO2 diffuses
into red blood cells, leaving only 7%
in the plasma as dissolved CO2.
Tissue cell
Interstitial
fluid
Some CO2 is picked up and
transported by hemoglobin.
1
CO2
Blood plasma
within capillary
Capillary
wall
8
In the HCO3– diffuse
from the plasma red blood cells,
combining with H+ released from
hemoglobin and forming H2CO3.
9
Carbonic acid is converted back
into CO2 and water.
10
CO2 formed from H2CO3 is unloaded
from hemoglobin and diffuses into the
interstitial fluid.
CO2
Red
blood
cell
3
4
H2CO3
Carbonic acid Hb
5
+ H+
Bicarbonate
However, most CO2 reacts with water
in red blood cells, forming carbonic
acid (H2CO3), a reaction catalyzed by
carbonic anhydrase contained. Within
red blood cells.
Most of the HCO3– diffuse
into the plasma where it is
carried in the bloodstream to
the lungs.
2
Hemoglobin
picks up
CO2 and H+
6
HCO3–
4
7
CO2
H2O
3
CO2 transport
from tissues
CO2 produced
7
HCO3–
To lungs
CO2 transport
to lungs
HCO3–
8
HCO3– +
H+
11
5
Carbonic acid dissociates into a
biocarbonate ion (HCO3–) and a
hydrogen ion (H+).
H2CO3
Hb
9
Hemoglobin
releases
CO2 and H+
H2O
CO2
6
Hemoglobin binds most of the
H+ from H2CO3 preventing the H+
from acidifying the blood and thus
preventing the Bohr shift.
Figure 42.30
CO2
CO2 10
CO2 11
Alveolar space in lung
CO2 diffuses into the alveolar
space, from which it is expelled
during exhalation. The reduction
of CO2 concentration in the plasma
drives the breakdown of H2CO3
Into CO2 and water in the red blood
cells (see step 9), a reversal of the
reaction that occurs in the tissues
(see step 4).
What about the CO2?
• As Hb releases O2, a binding site on
protein absorbs CO2. CO2 does not
bind to heme group (20%).
• 8% dissolved in the blood plasma.
• 72 % diffuses from plasma  RBC
cytoplasm and converted by enzyme
+
into H2CO3 HCO3 + H ions.
(a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4
O2 saturation of hemoglobin (%)
100
O2 unloaded from
hemoglobin
during normal
metabolism
80
O2 reserve that can
be unloaded from
hemoglobin to
tissues with high
metabolism
60
40
20
0
0
20
Tissues during
exercise
40
60
80
100
Lungs
Tissues
at rest
PO2 (mm Hg)
(b) pH and Hemoglobin Dissociation
O2 saturation of hemoglobin (%)
100
Figure 42.29a, b
pH 7.4
80
60
pH 7.2
40
20
Bohr shift:
Additional O2
released from
hemoglobin at
lower pH
(higher CO2
concentration)
0
0
20
40
60
PO2 (mm Hg)
80
100
Control of Breathing in Humans
• The main breathing control centers
– Are located in two regions of the brain, the medulla
oblongata and the pons
Cerebrospinal
fluid
1
The control center in the
medulla sets the basic
rhythm, and a control center
in the pons moderates it,
smoothing out the
transitions between
inhalations and exhalations.
4 The medulla’s control center
also helps regulate blood CO2 level.
Sensors in the medulla detect changes
in the pH (reflecting CO2 concentration)
of the blood and cerebrospinal fluid
bathing the surface of the brain.
5
Pons
2 Nerve impulses trigger
muscle contraction. Nerves
from a breathing control center
in the medulla oblongata of the
brain send impulses to the
diaphragm and rib muscles,
stimulating them to contract
and causing inhalation.
Breathing
control
centers
Medulla
oblongata
Nerve impulses relay changes in
CO2 and O2 concentrations. Other
sensors in the walls of the aorta
and carotid arteries in the neck
detect changes in blood pH and
send nerve impulses to the medulla.
In response, the medulla’s breathing
control center alters the rate and
depth of breathing, increasing both
to dispose of excess CO2 or decreasing
both if CO2 levels are depressed.
Carotid
arteries
3
Aorta
Figure 42.26
In a person at rest, these
nerve impulses result in
about 10 to 14 inhalations
per minute. Between
inhalations, the muscles
relax and the person exhales.
Diaphragm
Rib muscles
6 The sensors in the aorta and
carotid arteries also detect changes
in O2 levels in the blood and signal
the medulla to increase the breathing
rate when levels become very low.
Controlling Breathing
• Respiratory Control Center – Medulla
Oblongata in brain.
• Impulses sent to diaphragm and
intercostal muscles contraction and
expand thoracic cavity (inhalation).
• No impulse, muscles relax and cavity
becomes smaller (exhalation).
• Part of ANS but can be voluntary.
Controlling Breathing
• If breathing stops, the PCO2 of plasma
rises.
• Causes pH to drop (increase in [H+]).
• Peripheral chemoreceptors in walls of
aorta and coratid arteries detect increase
in [H+].
• Send signals to respiratory control
center.
• Initiates breathing.
What does exercise do?
• Working tissue causes ↑ PCO2 in
plasma and ↓in pH.
• As [H+] ↑, chemoreceptors cause an ↑
in respiratory rate.
• Can you indefinitely hyperventilate?
• Why can people hold their breath
longer if they hyperventilate first?
The Ultimate Endurance Runner
• The extreme O2 consumption of the antelope-like
pronghorn:
– Underlies its ability to run at high speed over long
distances
Figure 42.31