4 - circulation and gas exchange
TRANSCRIPT
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Circulation and Gas Exchange
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Problem: How totransport O2 and nutrients
efectively in multicellularorganisms
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• Every organism must exchangematerials with its environment
• Exchanges ultimately occur at thecellular level by crossing the plasmamembrane
ns: 1. The delivery of O2 and nutrientsneeded
2. Removal of CO2 and wastes
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In unicellular organisms, theseexchanges occur directly with the
environment
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• mall molecules can move between
cells andtheir surroundings by diusion
• !ifusion is only e"cient over smalldistances because the time it ta#es todifuse is proportional to the s$uare o%the distance
Tissue thickness
Rate of !iusion&nimals have developed cavities and
circulatory systems to transport gasses
and nutrients and to reduces the' (
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The increase in animal
size through evolution
led to many steps in
delivering O2 and
nutrients to where theyare needed
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Figure 42.1
Gills are an example of a specialized exchange
system in animals
O2 diffuses from the water into blood essels
!O2 diffuses from blood into the water
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Figure 42.2b
(b) The planarian Dugesia, a flatworm
Mouth
Pharyn!astrovascular
cavity
" mm
)latworms have a gastrovascularcavity and a *at body that minimi+es
difusion distances
& "astrovascular cavity %unctions in both digestion
and distribution o% substances throughout the body
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The #irculatory $ystem
-"ump # heart$s%
-Fluid # blood or
hemolymph
-&essels # interconnecting ascular
components
he Circulatory ystem
&ll circulatorysystems, -open orclosed. have/
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Figure 42.'a
(a) %n open circulatory system
&eart
&emolymph in sinuses
Pores
Tubular heart
Hemolymph baths the organs directly
(b) % l d i l t t
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(b) % closed circulatory system
'orsalvessel(main
heart)
%uiliaryhearts
$mall
branch vesselsin each organ
&eart
nterstitial fluid
lood
*entral vessels
blood is con0ned to vessels and is distinct %rom
the interstitial *uid
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Organi+ation o% 1ertebrate
Circulatory ystems
• Humans and other vertebrates havea closed circulatory system calledthe cardiovascular system
• ypes o% blood vessels/ arteriesarterioles veins venules and ca#illaries
• lood *ow is one way in thesevessels3 &rteries and veins aredistinguished by the direction o%
blood *ow, not by O2 content
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• $eins carry blood to theheart
• %rteries carry blood away
%rom the heart
&rteries and 1eins
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$ingle circulation+ fish
%rtery
&eart+%trium (%)
*entricle (*)
*ein
!illcapillaries
odycapillaries
ey Oygen-rich blood
Oygen-poor blood
; ony 0shes, rays, andshar#s have sin"lecirculation with a two&chambered heart
- In sin"le circulation,blood leaving the heartpasses through twocapillary beds be%ore
returning
- lood enters through anatrium and is pumpedout through a ventricle
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$ystemic circuit
$ystemiccapillaries
%trium
(%)
.ungand s/incapillaries
%trium
(%)
0ight .eft
*entricle (*)
Pulmocutaneous circuit
ey Oygen-rich blood
Oygen-poor blood
(mphibians and reptiles)
)rogs and amphibians havea three&chambered
heart/ two atria and oneventricle
ouble circulation
Figure 42 4c
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Figure 42.4c
ey Oygen-rich blood
Oygen-poor blood
'ouble circulation+mammal
Pulmonary circuit
.ungcapillaries
$ystemiccapillaries
$ystemic circuit
0ight .eft
% %
**
!ouble circulation maintainshigher blood pressure in theorgans than does singlecirculation
'ammals -and birds. alsohave a double circulation
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Mammals and birds have a four-chambered
heart with two atria and two ventricles
*he left side of the heart pumps and receies onlyoxygen+rich blood) while the right side receies and
pumps only oxygen+poor blood
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• lood begins its *ow with the ri"htventricle pumping blood to the lungsvia the #ulmonary arteries
• In the lungs, the blood loads O2 andunloads CO2
• Oxygen;rich blood %rom the lungsenters the heart at the left atriumvia the #ulmonary veins
he >ulmonary Circuit
Figure 42 ,
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""
1Figure 42.,
$uperior
vena cava
Pulmonary
artery
#apillaries
of right lung
Pulmonary
vein
0ight atrium
0ight ventricle
nferior
vena cava
#apillaries of
abdominal organs
and hind limbs
%orta
%orta
.eft ventricle
.eft atrium
Pulmonary
vein
#apillaries
of left lung
Pulmonary
artery
#apillaries of
head and
forelimbs
3
4
5
2
6
"7
"8
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• lood is pumped through the aorta to thebody tissues by the left ventricle
(strongest muscle of the heart)
• lood returns to the heart through the
su#erior vena cava -blood %rom head,
nec#, and %orelimbs. and inferior venacava -blood %rom trun# and hind limbs.
• he superior vena cava and in%erior venacava *ow into the ri"ht atrium
he ystemic Circuit
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*he mammalian heart has a double circulation-
heart lungs heart systemic
*he two atria hae relatiely thin walls and sere as
collection chambers for blood returning to
the heart
*he entricles hae thicer walls $ left is the thicest%
and contract much more forcefully
n"s to Remember about a 'ammalian
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he aorta provides blood to theheart through the coronary arteries
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he heart is enclosed and held in placeby the pericardium
>ericardium
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Pulmonaryartery
Pulmonary artery
0ight
atrium .eft
atrium
%orta
$emilunar
(pulmonary) valve
$emilunar (aortic)
*alve
%trioventricular
(%*) valve
(bicuspid or mitral)
%trioventricular
(%*) valve
(tricuspid)
0ight
ventricle
.eft
ventricle
$alves o#en and close to allowblood *ow between chambers
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+i". ,&1, #.-
t $alves O#en and Close in Res#onse to Pres !ierences
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1alves are One;way
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-c. ricuspid valve open
C?> O) @IC?>I!1&A1E
CHO@!&E EB!IBE&E
>&>IAA&@
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he heart contracts and relaxes in a rhythmic cyclecalled the cardiac cycle
• (ystole ; he contraction, or
pumping, phase• !iastole ; he relaxation, or 0lling,
phase
-In re%erence to ventricles.
DOne complete cycle o% pumping and 0lling
is called the Cardiac Cycle
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%trial and
ventricular diastole"
79"
sec
796
sec
79 sec
%trial systole and
ventricular diastole
2
*entricular systole
and atrial diastole
/0ub /!ub
Aub onset o% systole-&1 valve closes.
!ub onset o% diastole
-&ortic valve closes.
he Cardiac Cycle
ne cardiac cycle 3.4 sec.
h bl d th h th h
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• heart rate, ;the number o% beats per minute/
2 beats5min• stroke volume& the amount o% blood
pumped in a single contraction/
3 m0
• cardiac out#ut ; the volume o% bloodpumped into the systemic circulation #erminute
6 05min 2 beats5min 7 3 m05beat
ow much blood moves through the hea
iac out#ut heart rate 7 stroke v
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9hat determines Cardiac OutputFCO-mAmin.
• Stroke Volume and HeartRate
-
9hen the heart beats %aster,more blood is pumped into thecirculation per minute
; 9hen the heart musclescontract harder, more blood is
emptied into system
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Cardiac muscle cells are sel%;excitable,and there%ore, autorhythmic
# Cardiac muscle cells repeatedlygenerate spontaneous action potentialsthat then trigger heart contractions
he Conduction ystem
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%ction potentials
travels through
gap :unctions
%tria and ventricles
have separate
conductive muscles
- no gap :unctions
between them
< i t i i th H t @h th i
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$ignals (yellow)from $% nodespread throughatria9
$% node(pacema/er)
;#!
he sinoatrial 8(%9
node, or pacema#er,sets the rate and timingat which cardiac musclecells contract
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$ignals (yellow)from $% nodespread throughatria9
" $ignals aredelayed at %*node9
%*node
$% node(pacema/er)
;#!
Impulses %rom the & node travel to theatrioventricular 8%$9 node wherethey are delayed
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$ignals (yellow)from $% nodespread throughatria9
" $ignals aredelayed at %*node9
2 undle branchespass signals toheart ape9
&eartape
undlebranches
%*node$% node
(pacema/er)
;#!
Bext, the impulses travel through thebundle branches -undle o% His. to the
heart apex, whereJ
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$ignals (yellow)from $% nodespread throughatria9
" $ignals aredelayed at %*node9
2 undle branchespass signals toheart ape9
$ignalsspreadthroughoutventricles9
6
Pur/in:efibers&eart
ape
undlebranches
%*node$% node
(pacema/er)
;#!
J they travel to the Purkine ;bers whicma#e the ventricles contract3
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The
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• he sym#athetic division speeds
up the pacema#er = norepinephrineand epinephrine
• he #arasym#athetic divisionslows down the pacema#er ;acetylcholine
Bervous system regulation
o% the pacema#er
1 l i h i l
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1essels in the circulatorysystem
1eins
&rteries
venules
Capillaries
&rterioles
ac# to the heart
&rteries have thic#er walls than veins to
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%rtery *ein
0ed blood cells
&rteries have thic#er walls than veins toaccommodate the high pressure o% blood
pumped %rom the heart
Figure 42.c
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0ed blood cell
#apillary
Capillaries have thin walls, the endothelium plus itsbasal lamina, to %acilitate the exchange o% materials
Capillaries are only slightly wider than ared
blood cell
he epithelial layer that lines blood vessels is
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asal lamina
;ndothelium
$moothmuscle
#onnectivetissue
*ein
#onnectivetissue
$moothmuscle
;ndothelium
#apillary
%rtery
%rteriole*enule
*alve
he epithelial layer that lines blood vessels iscalled the endothelium. It is smooth and
minimi+es resistance3
1elocity o% blood is lower in veins than in
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'irection of blood flowin vein (toward heart)
*alve (open)
$/eletal muscle
*alve (closed)
1elocity o% blood is lower in veins than inarteries3 o, why does blood continue to
*ow towards heartF
One;way valvesprevent bac#*ow
#eletal muscle
contraction alsomoves blood along
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lood )low 1elocity
• peed in which blood *ows isinversely #ro#ortional the totalcross;sectional area o% the vessels
• Ca#illaries have the hi"hest cumulative cross;sectional area,
there%ore blood moves slowestthrough the capillaries3
8 777 Collectively
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$ystolicpressure
'iastolicpressure
% o r t a
% r t e r i e s
% r t e r i o
l e s
#
a p
i l l a r i e s
* e n u
l e s
* e
i n s
* e n a e
c a v a e
P r e s s u r e
( m
m &
g )
"27"77
5747
67277
* e
l o c
i t y
( c m
ressure isgreatest inthe &orta
Collectively,capillarieshave thegreatest area
he thecross;sectional
area, thethe velocity o%blood
&elocity of blood flow is slowest in the capillary
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&elocity of blood flow is slowest in the capillary
beds) as a result of the high resistance and large
total cross+sectional area
3lood flow in capillaries is necessarily slow for
exchange of materials
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• wo mechanisms regulatedistribution o% blood in capillary beds
# Constriction or dilation of arteriolesthat supplycapillary beds -regulated by nerveimpulses , hormones, or other
chemicals. # Preca#illary s#hincters that control*ow o% bloodbetween arterioles and venules
Ca#illary +unction
Figure 42.1'Precapillary sphincters Thoroughfare
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channel
%rteriole
#apillaries
*enule
(a) $phincters relaed
%rteriole *enule
(b) $phincters contracted
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8a9
do e acell
Pores
Ca#illary
;ndothelial cells of capillaries fit together li/e a
:igsaw puzzle
%llows passage
of water soluble
substances
.ipid soluble substances
do not need the pores,
but pass through the cells
directly
The e7chan"e of substances across
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%rterial end
of capillary 'irection of blood flow*enous end
of capillary
Osmotic
pressure
lood
pressure
=et fluid movement out=T;0$TT%.>.?' ody cell
"ca#illary walls.
-
@egulated by blood pressure and osmoticpressure-lood proteins rarely pass through endotheliumand help maintain osmotic pressure
lood
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+i". ,&- #.-?1
Plasma 66@ of whole blood
Packed cellvolume orhematocrit
Red blood cells A6@ of whole blood
Bhite blood cells
/uy coatD1@
Platelets
@ hematocrit varies with species and with
stress levels9
loodComposition and
)unction
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What is Plasma?
• >lasma contains inorganic salts, sometimescalled electrolytes
• Plasma #roteins in*uence blood pH andhelp maintain osmotic balance between
blood and interstitial *uid• >articular plasma proteins %unction in lipid
transport, immunity, and blood clotting
• >lasma is similar in composition tointerstitial*uid, but plasma has a much higher proteinconcentration
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Cellular Elements of Blood
• uspended in blood plasma are two typeso% cells
# Red blood cells -erythrocytes. transport O23
he hormone erythro#oietin 8
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>l i t t t C ll i i t
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>luripotent tem Cells give rise toAymphoid and
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;rythrocytes
• @ed blood cells, or erythrocytes, are themost numerous blood cells
• hey contain hemo"lobin, the iron;containing protein that transports O2
• Each molecule o% hemoglobin binds up to
%our molecules o% O2• In mammals, mature erythrocytes
lac# nuclei and mitochondria
&emoglobin
&eme
ron
*One erythrocyte contains ~250 billion hemoglobinmolecules
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KLm
ur%ace view
ectioned view
-a. @C shape
@ed lood Cells
Have no nucleus ormembrane boundorganelles
How would the
biconcave shape o% thecells bene0t difusion o%O2F
RCE( 8
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• ac intracellular organelles necessary for cellular repair) growth) diision
• $hort .ife $pan $5126 days%
• 0uptured 0#As are destroyed in spleen) lier or bone marrow
–
"hagocytic 73!8s 9clear the debris:
RCE( 8
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Res#iration• =as e7chan"e supplies O2 %or cellular
respiration and disposes o% CO2
• Gas exchange occurs across speciali+edrespiratory sur%aces
$ til ti th i t
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(a) Marine worm
Parapodium
(functions as gill)
(b) #rayfish
!ills
(c) $ea star
Tube foot
!ills
#oelom
$entilation moves the respiratorymedium over the respiratory sur%ace
Figure 42.22a
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!ill filaments
!ill arch
loodvessels
!ill
arch
Bater
flow
Operculum
In 0sh gills, more than
K5M o% the O2 dissolved in the wateris removed as waterpasses over the
Figure 42.2'Tracheoles Mitochondria Muscle fiber
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2 9 8
C m
Tracheae
%ir sacs
;ternal opening (spiracles)
Trachea
%ir
%ir
sac Tracheole
ody
cell
oo# lungs o%
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oo# lungs o%the pider
ammalian @espiratory ystem
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.eft lung
=asal
cavity
(&eart)
Pharyn
.aryn
(;sophagus)
Trachea
0ight lung
ronchus
ronchiole
'iaphragm
ammalian @espiratory ystem
.ungs are encased in a membraneous
pleural sac
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+i". 11&1A #.A
8a9
Bater&;lledballoon
!ia#hra"m
Thoracic wall
i"ht #leural sac
0eft
lun"
Ri"ht
lun"
Pleural cavity ;lledwith intra#leural *uid
$isceral #leura
Parietal #leura
0eft #leural sac
/0un"
/Pleural sac
8b9
0olli#o#
pleural sac
that is filled
with fluid
between its cavity
he right lung has three lobes, the
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-b. Aateral view o% rightlung
&pex
uperior lobe
&BE@IO@
OE@IO@
-c. Aateral view o% le%tlung
Obli$ue 0ssur
In%erior lobe
>OE@IO@
he right lung has three lobes, thele%t lung has two lobes
Trachea
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(&eart)
ronchus
ronchiole
'iaphragm
&natomy o% &lveoli
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%lveoli
#apillaries
Terminal
bronchiole
ranch of
pulmonary vein(oygen-rich
blood)
ranch of
pulmonary artery
(oygen-poor
blood)
255 = N55 million alveoli in a human lung
y
e7chan"e occurs in the alveoli
• &lveoli lac# cilia and are susceptible
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• &lveoli lac# cilia and are susceptible
to contamination
• ecretions called surfactants coatthe sur%ace o% the alveoli
• >reterm babies lac# sur%actant and
are vulnerable to respiratory distresssyndrome treatment is provided byarti0cial sur%actants
ow much air can the lun"s holdF
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• he the volume o% air inhaled witheach breath ; P Q55ml -idal 1olume.
• )orced inhalationexhalation P 7 A-1ital capacity.
• here is always air le%t behind in thelungs P632A -residual volume.
ow much air can the lun"s holdF
Q = R A
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2 ;D&%.%TO=+ 'iaphragmrelaes (moves up)9
" =&%.%TO=+ 'iaphragmcontracts (moves down)9
'iaphragm
.ung
0ib cageepands asrib musclescontract9
0ib cagegets smaller
as rib musclesrela9
Aung volume increases as the rib muscles
and dia#hra"m contract
#ressure breathin", which pulls air into thelungs
>artial >ressure Gradients in Gas
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>artial >ressure Gradients in Gas
Exchange
• Partial #ressure is the pressureexerted by a particular gas in amixture o% gases
• Gases undergo net difusion %rom aregion o% higher partial pressure to aregion o% lowerpartial pressure
Bhen the chest e7#ands the volume
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of the lun"s increases. The #ressuree7erted by o7y"en within the lun"s
decreases therefore o7y"en diusesinto the lun"s
Ri"ht #leural sac
!ia#hra"m
O2>52 6R5 mmHg
>52 S 6R5 mmHg
Figure 42.2
"27"47
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"
Pulmonary
veins and
systemic
arteries
2
8
4
6
$ystemic
capillaries
%lveolar
capillaries
%lveolar spaces
nhaled air
O2#O2
#O2 O2ody
tissue
Pulmonary
arteries
and systemic
veins
lood
entering
alveolar
capillaries
%lveolar
epithelial
cells
;haled air 21
P#O 2PO 2
67 68
P#O 2PO 2
P#O 2PO 2
E67F68
792
P#O 2PO 2
"76
67
P#O 2PO 2
"76
67
P#O 2PO 2
i i
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@espiratory >igments
• Res#iratory #i"ments, proteins thattransport oxygen, greatly increase theamount o% oxygen that blood can
carry• &rthropods and many molluscs have
hemocyanin with copper as the
oxygen;binding component• In vertebrates, hemoglobin is
contained within erythrocytes
Poly#e#tide chain&emoglobin (&b)
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y# #
Gronatomwithinheme"rou#
Poly#e#tide chain
Poly#e#tide chai)eme "rou#s
&emoglobin (&b)
$tructure+•>our polypeptide
chains•>our iron-containing
heme groups
;ach hemoglobin
molecule binds to
four O2 molecules
P P T P P P
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OO
O
O
O
OO
OOO
O
OO
O
O
O
O
OO
OO
O
O
O
O
O
OO
O
OO
O
OO
O
O
O O2 Hb
PO2
PO2
PO2 T PO2 PO2 PO2
Only unbound O2 contributes to PO2 Figure 42.'6a
O l d d"77
@ )
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O2 unloaded
to tissues
at rest
O2 unloadedto tissues
during
eercise
57
47
67
27
7"77574767277
O 2
s a t u
r a t i o n o f h e m o
g l o b i n ( @
Tissues during
eercise
Tissues
at rest
.ungs
PO (mm &g)2
(a) PO and hemoglobin dissociation at p& 1962
ohr (hift
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(b) p& and hemoglobin dissociation
p& 196
p& 192
&emoglobin
retains less
O2 at lower p&(higher #O2concentration)
"77
57
47
67
27
7"77574767277
O
2 s a t u r a t i o n o f h e m o g l o b i n ( @ )
PO (mm &g)2
ohr (hift
C b i id " t
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Carbon io!ide "rans#ort
• ome CO2 %rom respiring cells difuses intothe blood and is transported in bloodplasma, bound to hemoglobin
• he remainder difuses into erythrocytesand reacts with water to %orm H2CON, which
dissociates into HU and bicarbonate ions-HCONV.
• In the lungs the relative partial pressures o%CO2 %avor the net difusion o% CO2 out o% the
blood
Control o% reathing in
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Control o% reathing inHumans
• In humans, breathing is usuallyregulated by involuntary mechanisms
• he breathing control centers are %oundin the medulla oblongata o% the brain
• he medulla regulates the rate anddepth o% breathing in response to pHchanges in the cerebrospinal *uid
Figure 42.2;
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=O0M%. .OO' p&
(about 196)
lood #O2 level falls
and p& rises9 lood p& fallsdue to rising levels of
#O2 in tissues (such as
when eercising)9Medulla detects
decrease in p& of
cerebrospinal fluid9
#erebrospinal
fluid #arotid
arteries
%orta
Medulla
oblongata Medulla receives
signals from ma:or
blood vessels9
$ensors in ma:or blood vessels
detect decreasein blood p&9
$ignals frommedulla to ribmuscles anddiaphragmincrease rateand depth of ventilation9
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• ensors in the aorta and carotid arteries
monitor O2 and CO2 concentrations in the
blood
• hese signal the breathing control centers,
which respond as needed• &dditional modulation o% breathing ta#es
place in the pons, next to the medulla
CO2 is the main determinant o% pH in
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CO2 is the main determinant o% pH in
the blood
How is pH regulatedF