Bài giảng Biology - Chapter 42: Circulation and Gas Exchange

Chapter 42Circulation and Gas ExchangeOverview: Trading with the EnvironmentEvery organism must exchange materials with its environmentAnd this exchange ultimately occurs at the cellular levelIn unicellular organismsThese exchanges occur directly with the environmentFor most of the cells making up multicellular organismsDirect exchange with the environment is not possibleThe feathery gills projecting from a salmonAre an example of a specialized exchange system found in animalsFigure 42.1Concept 42.1: Circulatory systems reflect phylogenyTransport systemsFunctionally connect the organs of exchange with the body cellsMost complex animals have internal transport systemsThat 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 environmentInvertebrate CirculationThe wide range of invertebrate body size and formIs paralleled by a great diversity in circulatory systemsGastrovascular CavitiesSimple animals, such as cnidariansHave a body wall only two cells thick that encloses a gastrovascular cavityThe gastrovascular cavityFunctions in both digestion and distribution of substances throughout the bodySome cnidarians, such as jelliesHave elaborate gastrovascular cavitiesFigure 42.2CircularcanalRadial canal5 cmMouthOpen and Closed Circulatory SystemsMore complex animalsHave one of two types of circulatory systems: open or closedBoth of these types of systems have three basic componentsA circulatory fluid (blood)A set of tubes (blood vessels)A muscular pump (the heart)In insects, other arthropods, and most molluscsBlood bathes the organs directly in an open circulatory systemHeartHemolymph in sinusessurrounding ogransAnterior vesselTubular heartLateral vesselsOstia(a) An open circulatory systemFigure 42.3aIn a closed circulatory systemBlood is confined to vessels and is distinct from the interstitial fluidFigure 42.3bInterstitialfluidHeartSmall branch vessels in each organDorsal vessel(main heart)Ventral vesselsAuxiliary hearts(b) A closed circulatory systemClosed systemsAre more efficient at transporting circulatory fluids to tissues and cellsSurvey of Vertebrate CirculationHumans and other vertebrates have a closed circulatory systemOften called the cardiovascular systemBlood flows in a closed cardiovascular systemConsisting of blood vessels and a two- to four-chambered heartArteries carry blood to capillariesThe sites of chemical exchange between the blood and interstitial fluidVeinsReturn blood from capillaries to the heartFishesA fish heart has two main chambersOne ventricle and one atriumBlood pumped from the ventricleTravels to the gills, where it picks up O2 and disposes of CO2AmphibiansFrogs and other amphibiansHave a three-chambered heart, with two atria and one ventricleThe ventricle pumps blood into a forked arteryThat splits the ventricle’s output into the pulmocutaneous circuit and the systemic circuitReptiles (Except Birds)Reptiles have double circulationWith a pulmonary circuit (lungs) and a systemic circuitTurtles, snakes, and lizardsHave a three-chambered heartMammals and BirdsIn all mammals and birdsThe ventricle is completely divided into separate right and left chambersThe left side of the heart pumps and receives only oxygen-rich bloodWhile the right side receives and pumps only oxygen-poor bloodA powerful four-chambered heartWas an essential adaptation of the endothermic way of life characteristic of mammals and birdsFISHES AMPHIBIANSREPTILES (EXCEPT BIRDS)MAMMALS AND BIRDSSystemic capillariesSystemic capillariesSystemic capillariesSystemic capillariesLung capillariesLung capillariesLung and skin capillariesGill capillariesRightLeft RightLeft RightLeft Systemic circuitSystemic circuitPulmocutaneouscircuitPulmonarycircuitPulmonarycircuitSystemiccirculationVeinAtrium (A)Heart:ventricle (V)ArteryGillcirculationAVVVVVAAAAALeft SystemicaortaRight systemicaortaFigure 42.4Vertebrate circulatory systemsConcept 42.2: Double circulation in mammals depends on the anatomy and pumping cycle of the heartThe structure and function of the human circulatory systemCan serve as a model for exploring mammalian circulation in generalMammalian Circulation: The PathwayHeart valvesDictate a one-way flow of blood through the heartBlood begins its flowWith the right ventricle pumping blood to the lungsIn the lungsThe blood loads O2 and unloads CO2Oxygen-rich blood from the lungsEnters the heart at the left atrium and is pumped to the body tissues by the left ventricleBlood returns to the heartThrough the right atriumThe mammalian cardiovascular systemPulmonary veinRight atriumRight ventriclePosteriorvena cavaCapillaries ofabdominal organsand hind limbsAortaLeft ventricleLeft atriumPulmonary veinPulmonaryarteryCapillariesof left lungCapillaries ofhead and forelimbs Anteriorvena cavaPulmonaryarteryCapillariesof right lungAortaFigure 42.511011546293378The Mammalian Heart: A Closer LookA closer look at the mammalian heartProvides a better understanding of how double circulation worksFigure 42.6AortaPulmonaryveinsSemilunarvalveAtrioventricularvalveLeft ventricleRight ventricleAnterior vena cavaPulmonary arterySemilunarvalveAtrioventricularvalvePosterior vena cavaPulmonaryveinsRight atriumPulmonaryarteryLeftatriumThe heart contracts and relaxesIn a rhythmic cycle called the cardiac cycleThe contraction, or pumping, phase of the cycleIs called systoleThe relaxation, or filling, phase of the cycleIs called diastoleThe cardiac cycleFigure 42.7SemilunarvalvesclosedAV valvesopenAV valvesclosedSemilunarvalvesopenAtrial and ventricular diastole1Atrial systole; ventricular diastole2Ventricular systole; atrial diastole30.1 sec0.3 sec0.4 secThe heart rate, also called the pulseIs the number of beats per minuteThe cardiac outputIs the volume of blood pumped into the systemic circulation per minuteMaintaining the Heart’s Rhythmic BeatSome cardiac muscle cells are self-excitableMeaning they contract without any signal from the nervous systemA region of the heart called the sinoatrial (SA) node, or pacemakerSets the rate and timing at which all cardiac muscle cells contractImpulses from the SA nodeTravel to the atrioventricular (AV) nodeAt the AV node, the impulses are delayedAnd then travel to the Purkinje fibers that make the ventricles contractThe impulses that travel during the cardiac cycleCan be recorded as an electrocardiogram (ECG or EKG)The control of heart rhythmFigure 42.8SA node(pacemaker)AV nodeBundlebranchesHeartapexPurkinjefibers2Signals are delayedat AV node.1Pacemaker generates wave of signals to contract. 3Signals passto heart apex.4Signals spreadThroughoutventricles.ECGThe pacemaker is influenced byNerves, hormones, body temperature, and exerciseConcept 42.3: Physical principles govern blood circulationThe same physical principles that govern the movement of water in plumbing systemsAlso influence the functioning of animal circulatory systemsBlood Vessel Structure and FunctionThe “infrastructure” of the circulatory systemIs its network of blood vesselsAll blood vesselsAre built of similar tissuesHave three similar layersFigure 42.9ArteryVein100 µmArteryVeinArterioleVenuleConnectivetissueSmoothmuscleEndotheliumConnectivetissueSmoothmuscleEndotheliumValveEndotheliumBasementmembraneCapillaryStructural differences in arteries, veins, and capillariesCorrelate with their different functionsArteries have thicker wallsTo accommodate the high pressure of blood pumped from the heartIn the thinner-walled veinsBlood flows back to the heart mainly as a result of muscle actionFigure 42.10Direction of blood flowin vein (toward heart)Valve (open)Skeletal muscleValve (closed)Blood Flow VelocityPhysical laws governing the movement of fluids through pipesInfluence blood flow and blood pressureThe velocity of blood flow varies in the circulatory systemAnd is slowest in the capillary beds as a result of the high resistance and large total cross-sectional areaFigure 42.115,0004,0003,0002,0001,0000AortaArteriesArteriolesCapillariesVenulesVeinsVenae cavaePressure (mm Hg)Velocity (cm/sec)Area (cm2)SystolicpressureDiastolicpressure50403020100120100806040200Blood PressureBlood pressureIs the hydrostatic pressure that blood exerts against the wall of a vesselSystolic pressureIs the pressure in the arteries during ventricular systoleIs the highest pressure in the arteriesDiastolic pressureIs the pressure in the arteries during diastoleIs lower than systolic pressureBlood pressureCan be easily measured in humansFigure 42.12ArteryRubber cuffinflatedwith airArteryclosed120120Pressurein cuff above 120Pressurein cuff below 120Pressurein cuff below 70Sounds audible instethoscopeSounds stopBlood pressurereading: 120/70 A typical blood pressure reading for a 20-year-oldis 120/70. The units for these numbers are mm of mercury (Hg); a blood pressure of 120 is a force that can support a column of mercury 120 mm high.1 A sphygmomanometer, an inflatable cuff attached to apressure gauge, measures blood pressure in an artery.The cuff is wrapped around the upper arm and inflated until the pressure closes the artery, so that no blood flows past the cuff. When this occurs, the pressure exerted by the cuff exceeds the pressure in the artery.2 A stethoscope is used to listen for sounds of blood flow below the cuff. If the artery is closed, there is no pulse below the cuff. The cuff is gradually deflated until blood begins to flow into the forearm, and sounds from blood pulsing into the artery below the cuff can be heard with the stethoscope. This occurs when the blood pressure is greater than the pressure exerted by the cuff. The pressure at this point is the systolic pressure.3 The cuff is loosened further until the blood flows freely through the artery and the sounds below the cuff disappear. The pressure at this point is the diastolic pressure remaining in the artery when the heart is relaxed.470Blood pressure is determined partly by cardiac outputAnd partly by peripheral resistance due to variable constriction of the arteriolesCapillary FunctionCapillaries in major organs are usually filled to capacityBut in many other sites, the blood supply variesTwo mechanismsRegulate the distribution of blood in capillary bedsIn one mechanismContraction of the smooth muscle layer in the wall of an arteriole constricts the vesselIn a second mechanismPrecapillary sphincters control the flow of blood between arterioles and venulesFigure 42.13 a–cPrecapillary sphinctersThoroughfarechannelArterioleCapillariesVenule(a) Sphincters relaxed(b) Sphincters contractedVenuleArteriole(c) Capillaries and larger vessels (SEM) 20 mThe critical exchange of substances between the blood and interstitial fluidTakes place across the thin endothelial walls of the capillariesThe difference between blood pressure and osmotic pressureDrives fluids out of capillaries at the arteriole end and into capillaries at the venule endAt the arterial end of acapillary, blood pressure isgreater than osmotic pressure,and fluid flows out of thecapillary into the interstitial fluid.CapillaryRedbloodcell15 mTissue cellINTERSTITIAL FLUIDCapillaryNet fluidmovement outNet fluidmovement inDirection of blood flowBlood pressureOsmotic pressureInward flowOutward flowPressureArterial end of capillaryVenule endAt the venule end of a capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary.Figure 42.14Fluid Return by the Lymphatic SystemThe lymphatic systemReturns fluid to the body from the capillary bedsAids in body defenseFluid reenters the circulationDirectly at the venous end of the capillary bed and indirectly through the lymphatic systemConcept 42.4: Blood is a connective tissue with cells suspended in plasmaBlood in the circulatory systems of vertebratesIs a specialized connective tissueBlood Composition and FunctionBlood consists of several kinds of cellsSuspended in a liquid matrix called plasmaThe cellular elementsOccupy about 45% of the volume of bloodPlasmaBlood plasma is about 90% waterAmong its many solutes areInorganic salts in the form of dissolved ions, sometimes referred to as electrolytesThe composition of mammalian plasmaPlasma 55%ConstituentMajor functionsWaterSolvent forcarrying othersubstancesSodiumPotassiumCalciumMagnesiumChlorideBicarbonateOsmotic balancepH buffering, andregulation of membranepermeabilityAlbuminFibringenImmunoglobulins(antibodies)Plasma proteinsIcons (blood electrolytesOsmotic balance,pH bufferingSubstances transported by bloodNutrients (such as glucose, fatty acids, vitamins)Waste products of metabolismRespiratory gases (O2 and CO2)HormonesDefenseFigure 42.15SeparatedbloodelementsClottingAnother important class of solutes is the plasma proteinsWhich influence blood pH, osmotic pressure, and viscosityVarious types of plasma proteinsFunction in lipid transport, immunity, and blood clottingCellular ElementsSuspended in blood plasma are two classes of cellsRed blood cells, which transport oxygenWhite blood cells, which function in defenseA third cellular element, plateletsAre fragments of cells that are involved in clottingFigure 42.15Cellular elements 45%Cell typeNumberper L (mm3) of bloodFunctionsErythrocytes(red blood cells)5–6 millionTransport oxygenand help transportcarbon dioxideLeukocytes(white blood cells)5,000–10,000Defense andimmunityEosinophilBasophilPlateletsNeutrophilMonocyteLymphocyte250,000400,000 Blood clottingThe cellular elements of mammalian bloodSeparatedbloodelementsErythrocytesRed blood cells, or erythrocytesAre by far the most numerous blood cellsTransport oxygen throughout the bodyLeukocytesThe blood contains five major types of white blood cells, or leukocytesMonocytes, neutrophils, basophils, eosinophils, and lymphocytes, which function in defense by phagocytizing bacteria and debris or by producing antibodiesPlateletsPlatelets function in blood clottingStem Cells and the Replacement of Cellular ElementsThe cellular elements of blood wear outAnd are replaced constantly throughout a person’s lifeErythrocytes, leukocytes, and platelets all develop from a common sourceA single population of cells called pluripotent stem cells in the red marrow of bonesB cellsT cellsLymphoidstem cellsPluripotent stem cells(in bone marrow)Myeloidstem cellsErythrocytesPlateletsMonocytesNeutrophilsEosinophilsBasophilsLymphocytesFigure 42.16Blood ClottingWhen the endothelium of a blood vessel is damagedThe clotting mechanism beginsA cascade of complex reactionsConverts fibrinogen to fibrin, forming a clotPlateletplugCollagen fibersPlatelet releases chemicalsthat make nearby platelets sticky Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K)ProthrombinThrombin FibrinogenFibrin5 µmFibrin clotRed blood cellThe clotting process begins when the endothelium of a vessel is damaged, exposing connective tissue in the vessel wall to blood. Plateletsadhere to collagen fibers in the connective tissue and release a substance thatmakes nearby platelets sticky.1The platelets form a plug that providesemergency protectionagainst blood loss.2This seal is reinforced by a clot of fibrin when vessel damage is severe. Fibrin is formed via amultistep process: Clotting factors released fromthe clumped platelets or damaged cells mix withclotting factors in the plasma, forming an activation cascade that converts a plasma proteincalled prothrombin to its active form, thrombin.Thrombin itself is an enzyme that catalyzes the final step of the clotting process, the conversion of fibrinogen to fibrin. The threads of fibrin become interwoven into a patch (see colorized SEM).3Figure 42.17Cardiovascular DiseaseCardiovascular diseasesAre disorders of the heart and the blood vesselsAccount for more than half the deaths in the United StatesOne type of cardiovascular disease, atherosclerosisIs caused by the buildup of cholesterol within arteriesFigure 42.18a, b(a) Normal artery(b) Partly clogged artery50 µm250 µmSmooth muscleConnective tissueEndotheliumPlaqueHypertension, or high blood pressurePromotes atherosclerosis and increases the risk of heart attack and strokeA heart attackIs the death of cardiac muscle tissue resulting from blockage of one or more coronary arteriesA strokeIs the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the headConcept 42.5: Gas exchange occurs across specialized respiratory surfacesGas exchangeSupplies oxygen for cellular respiration and disposes of carbon dioxideFigure 42.19Organismal levelCellular levelCirculatory systemCellular respirationATPEnergy-richmoleculesfrom foodRespiratorysurfaceRespiratorymedium(air of water)O2CO2Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gasesBetween their cells and the respiratory medium, either air or waterGills in Aquatic AnimalsGills are outfoldings of the body surfaceSpecialized for gas exchangeIn some invertebratesThe 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 gillis an extension of the coelom(body cavity). Gas exchangeoccurs by diffusion across thegill surfaces, and fluid in thecoelom circulates in and out ofthe gills, aiding gas transport. The surfaces of a sea star’s tube feet also function in gas exchange. GillsTube footCoelomFigure 42.20aMany segmented worms have flaplike gillsThat extend from each segment of their bodyFigure 42.20b(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 gillsand also function incrawling and swimming.GillParapodiaThe gills of clams, crayfish, and many other animalsAre restricted to a local body regionFigure 42.20c, d(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.GillsGillsThe effectiveness of gas exchange in some gills, including those of fishesIs increased by ventilation and countercurrent flow of blood and waterCountercurrent exchangeFigure 42.21Gill archWater flowOperculumGill archBlood vesselGillfilamentsOxygen-poorbloodOxygen-richbloodWater flowover lamellaeshowing % O2Blood flowthrough capillariesin lamellaeshowing % O2Lamella100%40%70%15%90%60%30%5%O2Figure 42.22aTracheaeAir sacsSpiracle(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.Tracheal Systems in InsectsThe tracheal system of insectsConsists of tiny branching tubes that penetrate the bodyThe tracheal tubesSupply O2 directly to body cellsAirsacBody cellTracheaTracheoleTracheolesMitochondriaMyofibrilsBody wall(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 42.22b2.5 µmAirLungsSpiders, land snails, and most terrestrial vertebratesHave internal lungsMammalian Respiratory Systems: A Closer LookA system of branching ductsConveys air to the lungsBranch from the pulmonary vein (oxygen-rich blood) Terminal bronchioleBranch from thepulmonaryartery(oxygen-poor blood)AlveoliColorized SEMSEM50 µm50 µmHeartLeft lungNasalcavityPharynxLarynxDiaphragmBronchioleBronchusRight lungTracheaEsophagusFigure 42.23In mammals, air inhaled through the nostrilsPasses through the pharynx into the trachea, bronchi, bronchioles, and dead-end alveoli, where gas exchange occursConcept 42.6: Breathing ventilates the lungsThe process that ventilates the lungs is breathingThe alternate inhalation and exhalation of airHow an Amphibian BreathesAn amphibian such as a frogVentilates its lungs by positive pressure breathing, which forces air down the tracheaHow a Mammal BreathesMammals ventilate their lungsBy negative pressure breathing, which pulls air into the lungsAir inhaledAir exhaledINHALATIONDiaphragm contracts(moves down)EXHALATIONDiaphragm relaxes(moves up)DiaphragmLungRib cage expands asrib muscles contract Rib cage gets smaller asrib muscles relax Figure 42.24Lung volume increasesAs the rib muscles and diaphragm contractHow a Bird BreathesBesides lungs, bird have eight or nine air sacsThat function as bellows that keep air flowing through the lungsINHALATIONAir sacs fillEXHALATIONAir sacs empty; lungs fillAnteriorair sacsTracheaLungsLungsPosteriorair sacsAirAir1 mmAir tubes(parabronchi)in lungFigure 42.25Air passes through the lungsIn one direction onlyEvery exhalationCompletely renews the air in the lungsControl of Breathing in HumansThe main breathing control centersAre located in two regions of the brain, the medulla oblongata and the ponsFigure 42.26PonsBreathing control centersMedullaoblongata DiaphragmCarotidarteriesAortaCerebrospinalfluidRib musclesIn a person at rest, these nerve impulses result in about 10 to 14 inhalationsper minute. Between inhalations, the musclesrelax and the person exhales. 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.Nerve impulses relay changes in CO2 and O2 concentrations. Other sensors in the walls of the aortaand carotid arteries in the neck detect changes in blood pH andsend nerve impulses to the medulla. In response, the medulla’s breathingcontrol center alters the rate anddepth of breathing, increasing bothto dispose of excess CO2 or decreasingboth if CO2 levels are depressed.The control center in themedulla sets the basicrhythm, and a control centerin the pons moderates it,smoothing out thetransitions betweeninhalations and exhalations.1Nerve impulses trigger muscle contraction. Nervesfrom a breathing control centerin the medulla oblongata of the brain send impulses to thediaphragm and rib muscles, stimulating them to contractand causing inhalation.2 The sensors in the aorta andcarotid arteries also detect changesin O2 levels in the blood and signal the medulla to increase the breathing rate when levels become very low. 6534The centers in the medullaRegulate the rate and depth of breathing in response to pH changes in the cerebrospinal fluidThe medulla adjusts breathing rate and depthTo match metabolic demandsSensors in the aorta and carotid arteriesMonitor O2 and CO2 concentrations in the bloodExert secondary control over breathingConcept 42.7: Respiratory pigments bind and transport gasesThe metabolic demands of many organismsRequire that the blood transport large quantities of O2 and CO2The Role of Partial Pressure GradientsGases diffuse down pressure gradientsIn the lungs and other organsDiffusion of a gasDepends on differences in a quantity called partial pressureA gas always diffuses from a region of higher partial pressureTo a region of lower partial pressureIn the lungs and in the tissuesO2 and CO2 diffuse from where their partial pressures are higher to where they are lowerInhaled airExhaled air1600.2O2CO2O2CO2O2CO2O2CO2O2CO2O2CO2O2CO2O2CO240 4540 45100 40104 40104 40120 27CO2O2AlveolarepithelialcellsPulmonaryarteriesBlood enteringalveolarcapillariesBlood leavingtissuecapillariesBlood enteringtissuecapillariesBlood leaving alveolar capillariesCO2O2Tissue capillariesHeartAlveolar capillariesof lung45Tissue cellsPulmonaryveinsSystemic arteriesSystemicveinsO2CO2O2CO2Alveolar spaces1243Figure 42.27Respiratory PigmentsRespiratory pigmentsAre proteins that transport oxygenGreatly increase the amount of oxygen that blood can carryOxygen TransportThe respiratory pigment of almost all vertebratesIs the protein hemoglobin, contained in the erythrocytesLike all respiratory pigmentsHemoglobin must reversibly bind O2, loading O2 in the lungs and unloading it in other parts of the bodyHeme groupIron atomO2 loadedin lungsO2 unloadedIn tissuesPolypeptide chainO2O2Figure 42.28Loading and unloading of O2Depend on cooperation between the subunits of the hemoglobin moleculeThe binding of O2 to one subunit induces the other subunits to bind O2 with more affinityCooperative O2 binding and releaseIs evident in the dissociation curve for hemoglobinA drop in pHLowers the affinity of hemoglobin for O2O2 unloaded fromhemoglobinduring normalmetabolismO2 reserve that canbe unloaded fromhemoglobin totissues with highmetabolism Tissues duringexerciseTissuesat rest100806040200100806040200100806040200100806040200LungsPO2 (mm Hg)PO2 (mm Hg)O2 saturation of hemoglobin (%)O2 saturation of hemoglobin (%)Bohr shift:Additional O2released from hemoglobin at lower pH(higher CO2concentration)pH 7.4pH 7.2(a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4(b) pH and Hemoglobin DissociationFigure 42.29a, bCarbon Dioxide TransportHemoglobin also helps transport CO2And assists in bufferingCarbon from respiring cellsDiffuses into the blood plasma and then into erythrocytes and is ultimately released in the lungsFigure 42.30Tissue cellCO2InterstitialfluidCO2 producedCO2 transportfrom tissuesCO2CO2Blood plasmawithin capillaryCapillarywallH2ORedbloodcellHbCarbonic acidH2CO3HCO3–H++BicarbonateHCO3–Hemoglobinpicks upCO2 and H+HCO3–HCO3–H++H2CO3HbHemoglobinreleasesCO2 and H+CO2 transportto lungsH2OCO2CO2CO2CO2Alveolar space in lung2134567891011To lungsCarbon dioxide produced bybody 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.Some CO2 is picked up and transported by hemoglobin.However, most CO2 reacts with water in red blood cells, forming carbonic acid (H2CO3), a reaction catalyzed bycarbonic anhydrase contained. Withinred blood cells.Carbonic acid dissociates into a biocarbonate ion (HCO3–) and a hydrogen ion (H+).Hemoglobin binds most of the H+ from H2CO3 preventing the H+ from acidifying the blood and thuspreventing the Bohr shift.CO2 diffuses into the alveolarspace, from which it is expelledduring exhalation. The reductionof CO2 concentration in the plasmadrives the breakdown of H2CO3 Into CO2 and water in the red bloodcells (see step 9), a reversal of the reaction that occurs in the tissues (see step 4).Most of the HCO3– diffuseinto the plasma where it is carried in the bloodstream to the lungs.In the HCO3– diffusefrom the plasma red blood cells, combining with H+ released from hemoglobin and forming H2CO3.Carbonic acid is converted back into CO2 and water.CO2 formed from H2CO3 is unloadedfrom hemoglobin and diffuses into the interstitial fluid. 1234567891011Elite Animal AthletesMigratory and diving mammalsHave evolutionary adaptations that allow them to perform extraordinary featsThe Ultimate Endurance RunnerThe extreme O2 consumption of the antelope-like pronghornUnderlies its ability to run at high speed over long distancesFigure 42.31Diving MammalsDeep-diving air breathersStockpile O2 and deplete it slowly