Respiration:
TheExchange
of Gases
Objectives
Introduction Explain how geesecan fly at altitudesas high or higher thanMt. Everest.Explainhow
humansadjustto life at high altitudes.
Mechanisms
of GasExchange
22.t Describethe threemain phasesof gas exchange.
22.2 Describe the propertiesof respiratory surfaces.Describefour types of respiratorysurfaces
and the fypes of animals that use them.
223 Explain how the amountof oxygen availablein air comparesto that availablein cold and
warm fresh water and salty water.
223 Explain how the structure of fish gills maximizesoxygen exchange.
22.4 Explain how a countercurentexchangemechanismin fish gills maximizesoxygen
fiansfer.
22.5 Explain how breathingafu is easierthan using water for gas exchange.
?2.5 Describe the trachealsystem of insects.
22.6 Describe the structuresand correspondingfunctionsof a mammalianrespiratorysystem.
22.7 Describethe impactof smoking on humanhealth.
?:2.E Comparehow humansand birds ventilate their lungs.
22.9 Explain how breathingis controlledin humans.
Transportof Gasesin the Body
22.10 Explain how blood transportsgasesbetweenthe lungs and tissuesof the body.
?2.11 Describethe functionsof hemoglobin.
22.12 Explain how a human fetus obtains oxygen prior to and immediatelyafter birth.
KeyTerms
gasexchange
respiration
respiratory surface
gill
trachea
lung
ventilation
countercurrentexchange
216
tracheole
diaphragm
pharynx
larynx
vocal cord
bronchus
bronchiole
alveolus
emphysema
breathing
negativepressurebreathing
vital capacity
breathingcontrolcenter
hyperventilating
partialpressure
hemoglobin
Chapter 22 Respiration: The Exchange of Gases
217
Word Roots
alveol- : a cavity (alveoli: one of the dead-end,multilobed air sacs that constitute the gas exchange
surface of the lungs)
counter- : opposite (countercurrentexchange:the opposite flow of adjacent fluids that maximizes transfer rates)
LectureOutline
Introduction Surviving in Thin Air
A. Review:Cellularrespiration:Animalsneedto obtain oxygenand glucoseand rid themselvesof wastecarbondioxide(Chapter6; Figures6.1, 6.2A, and 6.8).
B. Life at high altitudeimposesmany changeson the organsand tissuesthat function in
respiration.
1. Peopleborn in and adaptedto high altitudes have relatively large hearts,more red
blood cells,and elevatedhemoglobinconcentrations.
2. A shortperiodof conditioningwill help those living in lower altitudes acclimateto
higher altitudes.Fasterheart rate and larger capillary diameter are replacedover
time with deeperand more rapid ratesof breathing,more capillaries, and higher
numbersof red blood cells and levels of hemoglobin.
3. Many animalsare capableof exchanginggasesfrom environmentshumanswould
find inhospitable.Somebirds can standthe cold and low oxygen concentrationsof
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f#ffi,"ffihffi"1';ffi"::ff
that hold oxygen.
I. Mechanisms of Gas Exchange
Modute 22.1 Overtiew:Gasexchangeinvolvesbreathing,the transportof gases,and the servicing of tissuecells.
A. Breathinginvolvesinhaling02 and exhalingCO2 (Figwe 22.1)B. The transportof gasesinvolvesdiffrrsion into and transportby hemoglobin in the red
blood cellsof the circulatorysystem.
C. Blood supplieseverycell with 02 andpicks up wasteC02.
Module 22.2 Anmals exchange02 and CO2 through moist body surfaces.
A. Rmpiratory surfacesvary amonganimal groups. However,what all respiratory surfaceshavein commonis that they mustbe moist, thin, and extensive.Gasesmust be
dissolvedin waterbeforethey can diffrrsein or out. In eachpart of Figure 22.24-D,
the circle representsa crosssectionof the animal's body in the region of the respiratory
surface,and the greencolor representsthe respiratory surfaces.
"skin-breathers"must live in moist environments
B. Earthworms(Module18.11)and other
to keep their skinsmoist. Small size or flatnessprovides the high ratio of respiratory
surfaceto body volumerequiredfor efficient gas exchangebetweenenvironmentand
cells (Figure22.24).
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Instructor's Guide to Tbxt and Media
C. Gills haveevolvedin most aquatic animalsto increasethe respiratorysurface.They
generallyproject from the body surface(Figure22.28).
D. Tlacheaeare specializedbreathing tubesfound in insects(Module 18.13).These
branchedtubesbring externalgasesdirectly to the inner cells without the aid of the
circulatorysystem(Figure 22.2C).
(Figure22.2D).They are comE. Lungs are found in the majority of terrestrialvertebrates
posedof branchedtubesending in tiny internalsacslined with a moist epithelium.
Gasesare carriedbetweenthe lungs and body cells by the circulatorysystem.
Module 223 Gills are adaptedfor gas exchangein aquaticenvironments.
A. The chief advantageof exchanginggaseswith wateris that energydoesnot haveto be
expendedto keep the transfer surface wet.
in air, andthe
B. However,the concentrationof 02 is only 3-5Voof its concentration
wanner and saltier the water, the less 02 it can carry. Consequently,gills must be very
efficient to exffact 02 from water.
"inhaling" water
C. Energyis expendedas a fish coversits gill surfaceswith waterby
"exhaling"the wateracrossthe gills
with its operculaclosedand mouth opened,and
with its mouth closed and opercula opened.The processof increasingcontactof the
surfaceareawith oxygenis called ventilation regardlessif it's a fish, bird, or any other
animal.
D. Oxygen-poorblood enterseach gill filamentand crossesthe lamellae(red bloodcells
ftavel single file here),picking uP Oz and leaving COz(Figure22.3).
Module 22.4 Countercurrentflow in the gills enhances02 transfer'
A. Countercurrent exchangeis a generalprincipleof transferfound in manyanimalsystems.
(Module25.2)
NOTE: For example,a countercurrentsystemis usedin thermoregulation
and to enhancewater reabsorptionin the kidneys (Module 25.11).
from a fluid flowing in one
exchangeis the transferof a substance
B. Countercurrent
direction to anotherfluid moving in the oppositedirection.
C. Oppositeflows maintain a diffusion grcdientthat enhancesthe transferof the substance,
02 in the caseshown(Figure 22.4).
NOTE: To impressstudentswith the efficiency that resultsfrom this alrangement,diagram a transfer systemin which both fluids flow in the samedirection.
D. This mechanismis so effrcientin fish that their gills removemore than 80Voof the oxygen dissolvedin the water flowing through them.
Module 22.5 Tt'tetrachealsystemof insects providesdirect exchangebetweenthe air and body
cells.
A. Ah containsmuch more 02 than an equalvolume of water,and air is easierto move
than water.Thus, terrestrial animals expendless energyin ventilating their respiratory
surfaces.
B. Tracheaein an insect branch throughout the body, conveyingair directly to body cells
(Figure22.5A,B, and C).
C. Includedin the systemare trachealair sacsthat work like bellowswhen muscles
aroundthem alternatelycontract and relax, moving air out and in.
D. Wateris conserved,and respiratorysurfacesremainmoist becauseonly the ultimate
narrowesttubes,the tracheoles,containfluid. It is acrossthe tracheolesthat gas
exchangeoccurs.
Chapter 22 Respiration: The Exchangeof Gases
2t9
Module 22.6 Tenestrial vertebrateshave lungs.
the cfuculatorysysA. Since lungs are restrictedto one part of the body,unlike tracheae,
tem must be involved in transportingthe gasesto and from body cells.
B. Amphibianssupplementtheir lungs with skin breathing,but all otherterrestrialvertebrates(and aquaticreptiles and mammals)haveefficientlungsonly.
C. The humanrespiratorysystemincludes:the nasalcavity (filters,wanns,humidifies,and
samplesodors of incoming air), the pharynx (conftols the passageof air through the
mouth region and into the larynx [Module 2I.6]), and a branchedsystemof tubes(trachea and bronchi) that lead into the lungs.(Figure22.6A).
D. Exhaling throughthe vocal cords of the larynx producessounds.
NOTE: This branched systemis anotherexampleof the hierarchicalorganizationof life
(Module1.1).
E. Lungs include the ultimate branchesof the bronchioles and the grapelikeclustersof
alveoli. Gasexchangeoccursacrossthe alveolarsurfaces(Figure22.68).
F. All surfacesof the respiratory systemare lined by moist epithelium.In all but the alveoli and smallestbronchioles,cilia and a thin film of mucusthat helpseliminatedust,
pollen, etc., cover this tissue.
G. A musculardiaphragm helps move air in and out of the lungs.
H. 02 in inhaledair dissolvesin a film of moisturelining the alveoli,thendiffirsesacross
the epithelial cells and into a web of capillariesthat surroundsthe alveolus.CO2 diffuses the other way (Figure 22.6C).
Module 22.7 Conne*tion: Smoking is one of the deadliestassaultson our respiratorysystem.
A. Mucus covering the epithelium of the respiratorysystemtrapsparticlesand microorganisms that are then swept out of the respiratory systemby the actionof cilia.
Review:Cilia Module 4.18).
inhabiting the linB. Microorganismsand particles are also phagocytizedby macrophages
ing of the respiratory system.
manypotentially
of chemicals,
C. A breathof air in a polluted city may containthousands
harmful. Air pollutants such as sulfur dioxide, carbonmonoxide,and ozoneare associated with seriousrespiratory diseases,and asbestosfibers and radioactiveradon gas
have been linked with lung cancer.
D. Tobaccosmokeis one of the worst sourcesof toxic air pollutants.Componentsare
This
known to irritate epithelial cells and inhibit or destroycilia and macrophages.
coughing
of
smokers
the
frequent
lungs'
alveoli;
to
reach
the
of
the
toxins
more
allows
is the respiratory system's attemptat cleaningitself.
E. Emphysema is a diseaseof cigarettesmokerscharacterizedby the alveoli becoming
brittle and eventually rupturing.
F. Lung cancer,causedby exposureto tobaccosmoke,is nearly alwaysfatal
(Figure22.lA,B).
disease.The list
NOTE: The leading causeof deathamong smokersis cardiovascular
of the adverseeffects of smoking is a long one; someof the more importantones to
emphasizeare the effects of both active and passivesmokingon prenataldevelopment,
infants, and children. Theseeffectsinclude (but are not limited to) an increasedprobability of cleft lip and cleft palate,decreasedtransferof vitamin C to the fetus, increased
risk of low birth weight babies,increasedrisk of allergies,delayedlung development,
and increasedrisk of pneumonia.Smokinghasbeenlinked to SIDS(suddeninfant
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Instructor's Guide to Textand Media
deathsyndrome).Smokersaremorelikely to experiencean ectopicpregnancythan nonsmokersare, and smokerstaking birth control pills are more likely to experience
adversesideeffects(Module27.8).
Module 22.8 Breathing ventilatesthe lungs.
A. During inhalation,the rib cageexpands,the rib musclesand diaphragmcontract,and
the chestexpands.The lungsalsoincreasein size. Thesechangesreducethe air pressure within the alveoli, and air movesin as a result of the higher pressureoutside(Figwe 22.8A).This is callednegativepnessurebreathing.
B. During exhalation,the rib musclesand diaphragmboth relax, decreasingthe volumeof
the rib cageand forcing air out.
NOTE: The elasticcartilageholding the rib cagetogetherhelps increaseand decrease
the rib cage'svolume.
C. The normal volumeof eachbreathis about 500 mL. The maximum volume that one
can inhaleand exhale,the vital capacit5 is about3500 mL and 48@ mL for collegeage femalesand males,respectively.The air that remainsin the lungs after complete
exhalationis the residualvolume.This is proportionally greater(relative to vital capacity) in older and more diseasedpeople.
D. Gas-exchange
systemsof birds aremore efficientthan most mammals'gas-exchange
systemsare.Birds maintaina one-wayflow of air betweentwo air sacsin additionto
lungs.The sacsact like bellowsand are not involvedwith gas exchange.The air tubes
within the lungs haveno residualvolume of air becauseall the air travels through the
lungs in one direction while the blood travelsin the oppositedirection, anotherexample
of a countercurrentexchangesystem(Figure 22-gB).
Module 22.9 Breathtngis automaticallycontrolled.
A. Althoughbreathingcan be consciouslycontrolled,most of the time automaticconftol
centersin our brain regulateour breathingmovements(Figure 22.9).
B. Breathing contnol centers are locatedin the lower parts of the brainstem,the pons and
the medullaoblongata(Module28.15).About lFl4 times a minute, nervesfrom those
areassignal the diaphragmand rib musclesto contract.
C. Increasedcellularrespirationcausesincreasedconcentrations
of CO2 in the blood. CO2
reactswith water to form carbonicacid, lowering the pH. The medulla sensesthe pH
drop and increasesthe rate and depthof breathing,thus eliminating more CO2 from the
blood in the lungs.Hyperventilationalso causesan increasein the pH of the blood.
NOTE: This is one of the mechanismsthat results in panting during and after shenuous
exercise.Lactic acid buildup also contributesto the acidity of the blood during strenuous exercise(Module6.15).
D. Dwing severedepressionof 02 levelsin the blood, sensorson arteriesnear the heart
signal the breathingcontrol center.This responsemay occur at high altitudes,where
requiredlevels of 02 cannotbe obtainedby normal breathing.
II. Tbansport of Gasesin the Body
Module 22.10 Blood ffansportsthe respiratoryg:rses,with hemoglobincarrying the oxygen.
A. The humancirculatory systemfunctionsin gastransport.One side of the heart pumps
O2-poor,CO2-richblood from the body to the lungs, and the other side of the heart
pumpsO2-rich,CO2-poorblood from the lungsto the rest of the body (Figure22.lOA).
Chapter 22 Respiration: The Exchangeof Gases
221
B. Every gasin a mixtureaccountsfor a portion (that gas'spartial pressure)of the mixAt eachlocation (lungs and tissues),gasesare exchangedas they
ture's total pressure.
diffuse alongtheir own partial pressuregradient.
C. 02 is not very solublein water.Hemoglobin in red blood cells has a much higher
affinity for 02 thanwater.Hemoglobinconsistsof four polypeptidechains,eachchain
attachedto a hemechemicalgroup with an iron atom in its center.Eachiron atom can
carry one 02 molecule(Figure22.108).
Module 22.11 HemoglobinhelpstransportCO2 and buffer the blood.
A. Chemicalmoderationof pH level is known as buffering.By helpingtransportCO2,
hemoglobinhelpsbufferthe blood.
B. Within red blood cells,CO2reactswith water to form H2CO3.This breaksinto acidic
H* and basicHCO3- ions more quickly in red blood cells underthe control of an
Hemoglobinpicks up most H+ ions and allows
enzymethere(carbonicanhydrase).
most HCO3- ions to diffuseback into the plasma.This providesa buffer in the blood
that will reactwith anyH* ions that are picked up elsewhere(Figure22.IlA).
C. When blood flows throughthe lungs,the processis reversed.H- ions are given up by
the hemoglobin,reactingwith the HCO3- ions to form H2CO3.This is then converted
back into CO2,andthe CO2diffusesfrom the blood to the air (Figure22.lIB).
Module 22.12 Cowrcction:Thehumanfetus exchangesgaseswith the mother'sbloodstream.
A. The fetuslies within a waterybath of amnioticfluid. Its lungs are filled with this fluid.
B. Capillariesfrom the fetal blood supply (through the umbilical cord) mix with capillaries
of the uterusin the placenta(Figure22.12).
C. A countercurrentarrangementof thesecapillaries facilitates the transferof gases
betweenfetus and mother.A fetus also has a different type of hemoglobinfrom the
mother.This fetal hemoglobinhas a higher affinity for oxygenthan normal adult hemoglobin, thus enhancingthe ftansfer of 02 from mother to fetus.
in the blood
D. When the babyis born,when placentaltransferstops,CO2concentration
increases,lowering the pH and stimulating the breathingcenter,causingthe baby to
take its first breath.
Preview: Refer to this modulewhen discussingfetal changesthat take place during the
third rimester of pregnancy(Module 27.17).
ClassActivities
L
A bell-jar modelof lungswith a diaphragmcanbe built or purchasedfrom biologicalsupply compatube andplaceballoonson the two ends(thesewill be the
nies.To build a model,takeaY-shaped
tubein a stopper,andplacethis in theneckofthe belljar.
lungs),securethe stemoftheY-shaped
Securea pieceof rubberacrossthewide,openend of the bell jar (this will be the diaphragm);the bell
jar itself playsthe role of the thoraciccavity.When the rubberdiaphragmis pulled on, the volume of
the bell jar increasesandair will enterthe balloons.When the rubber diaphragmis allowed to return to
its originalposition,the volumeof ttrebell jar will decreaseand air will be forcedout of the balloons.
the forcesthat fill and emptymammalianlungs.
This is an elegantlysimpleway of demonstrating
2.
of the nonsmokers
versusthe smokersin the class.Let
Find theaveragepulserateandbloodpressures
the smokersgo outsideto smokeandwhen they comeback, seehow their averagepulse rate and
bloodpressurehavechanged.
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Instructor's Guide to Textand Media
Acetates
Transparency
Figure22.l
Figure22.2A
Figure22.28
Figure22.2C
Threephasesofgas exchange
The entireouterskin
Gills
Tracheae
Figure22.2D
Figure22.3
Figwe22.4
Figure22.5A
Figure22.5C
Figure22.6A
Figure22.68
Figure22.8A
Figure22.88
Figwe229
Figure22.9
Figure22.lOA
Figrrre22.lOB
Figure22.llA
Figure22.llB
Figare22.12
Lungs
The sffuctureof fish gills
flow in a fish gill
Countercurrent
The trachealsystemof an insect
Trachealconnectionsto bodycells
The humanrespiratorysystem
The structureof alveoli
How a humanbreathes
How a bird breathes
Control centersthat regulatebreathing(Layer 1)
Control centersthat regulatebreathing(Layet 2)
Gasexchangein the body
Hemoglobinloadingandunloadingof 02
CO2transportfrom the bodytissuesinto the blood
CO2transportfrom the bloodinto the lungs
A humanfetusandplacentain the uterus
Media
Seethe beginningof this book for a completedescription of all media availablefor instructorsand students.Animationsand videos are available in the Campbell Image PresentationLibrary. Media Activities
andThinking as a Scientist investigationsare availableon the studentCD-ROM and web site.
Activities andThinking as a Scientist
Module Number
Web/CDActivity 22A: TheHumnnRespiratorySystem
Web/CDActivity 228; Transportof RespiratoryGases
BiologyLabsOn-Line;Hemoglobinlab
22-6
22-ll
22-ll