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What is Gas Exchange?Gas exchange -> supplies oxygen for cellular respiration -> disposes of carbon dioxideGases diffuse down pressure gradients in the lungs and other organs b/c of differences in partial pressure.

Ok but what is Partial Pressure?Partial pressure -> the pressure exerted by a particular gas in a mixture of gasesA gas diffuses from a region of higher partial pressure to a region of lower partial pressureIn the lungs and tissues -> O2 and CO2 diffuse from areas of higher partial pressure to lower partial pressure

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings1Partial Pressure -> similar to concentration, but for gasesWhere does an organisms O2 come from?Respiratory MediaAnimals can use air or water as a source of O2, or respiratory medium. In a given volume, there is less O2 available in water than in air.SoObtaining O2 from water requires greater efficiency than air breathing.Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings2Humans -> 25% of O2 from airFish-> 80% of O2 from waterWhat are respiratory surfaces?Large, thin, moist tissue used for gas exchangeGases diffuse across respiratory surfacesCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings3How do cnidarians perform gas exchange?Cnidarians (i.e. jellies) -> gas exchange occurs in all cells -> no specific respiratory tissue

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsWhat about annelids? Gas exchange performed through the skinHemoglobin present in circulatory system

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Gills -> outfoldings of the body that create a large surface area for gas exchangeParapodium (functions as gill)(a) Marine wormGills(b) Crayfish(c) Sea starTube footCoelomGills6Figure 42.21 Diversity in the structure of gills, external body surfaces that function in gas exchange

Ventilation moves the respiratory medium (i.e. air or water) over the respiratory surface.

Aquatic animals move through water or move water over their gills for ventilation.Fish gills -> countercurrent exchange -> is when blood flows in opposite direction to water passing over gills -> blood always has less O2 than the water moving over it

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings7Maximizes diffusion -> efficiency

How do fish gills work?Anatomy of gillsGillarchWaterflowOperculumGillarchGill filamentorganizationBloodvesselsOxygen-poor bloodOxygen-rich bloodFluid flowthroughgill filamentLamellaBlood flow throughcapillaries in lamellaWater flowbetweenlamellaeCountercurrent exchangePO2 (mm Hg) in waterPO2 (mm Hg) in bloodNet diffusion of O2from water to blood1501209060301108020Gill filaments501408Fun fact: gills would work really poorly on land

How do insects do gas exchange?Tracheal system -> tiny branching tubes that penetrate the body.Tracheal tubes supply O2 directly to all body cells

AlsoRespiratory and circulatory systems are separate.Larger insects must ventilate their tracheal system to meet O2 demands, i.e. in flightCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings9

Air sacsTracheae = air tubesExternal opening:spiraclesBodycellAirsacTracheoleTracheolesMitochondriaMuscle fiber2.5 m Body wallTracheaAir external openings spiracles10Figure 42.23 Tracheal systems

The circulatory system (open or closed) transports gases between the lungs and the rest of the body.Lungs=infolding of body surfaceSize and complexity of lungs increases with organisms metabolic rate.

How do terrestrial vertebrates do gas exchange?Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings11How about mammals, specifically?System of branching ducts/air tubes conveys air to the lungs.Air inhaled through the nostrils --> pharynx --> larynx --> trachea --> bronchi --> bronchioles --> alveoli = site of gas exchange.Alveoli -> sacs of thin epithelium wrapped in capillariesExhaled air passes over the vocal cords to create sounds.

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Human Respiratory System

PharynxLarynx(Esophagus)TracheaRight lungBronchusBronchioleDiaphragmHeartSEMLeftlungNasalcavityTerminalbronchioleBranch ofpulmonaryvein(oxygen-richblood)Branch ofpulmonaryartery(oxygen-poorblood)AlveoliColorizedSEM50 m50 m13 How does breathing ventilate the lungs?Amphibians -> positive pressure breathing, ->forces air down the trachea.Mammals -> negative pressure breathing, ->pulls air into the lungs by varying volume/air pressure. Lung volume increases as the rib muscles and diaphragm contract.Tidal volume -> volume of air inhaled/breathMaximum tidal volume -> vital capacity. Residual volume -> volume of air that remains in the lungs after exhalationCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings14

Negative pressure breathing: H --> LLungDiaphragmAirinhaledRib cageexpands asrib musclescontractRib cage getssmaller asrib musclesrelaxAirexhaledEXHALATIONDiaphragm relaxes(moves up)Volume decreasesPressure increasesAir rushes outINHALATIONDiaphragm contracts(moves down)Volume increasesPressure decreasesAir rushes in15Figure 42.25 Negative pressure breathing

How do birds breathe?Eight-nine air sacs function as bellows that keep air flowing through the lungs.Air passes through the lungs in one direction only.

AlsoEvery exhalation completely renews the air in the lungs.Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings16

The Avian Respiratory SystemAnteriorair sacsPosteriorair sacsLungsAirLungsAir1 mmTracheaAir tubes(parabronchi)in lungEXHALATIONAir sacs empty; Lungs FillINHALATIONAir sacs fill17Figure 42.26 The avian respiratory system

How do humans control their breathing?Breathing control -> two regions of the brain, medulla oblongata & ponsMedulla -> regulates the rate and depth of breathing in response to pH changes: CO2 levels in the cerebrospinal fluid -> adjusts breathing rate and depth to match metabolic demandsPons -> regulates the tempoCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings18Sensors in the aorta and carotid arteries monitor O2 and CO2 concentrations in the blood -> secondary control over breathingAlsoCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings19

Automatic control of breathingBreathingcontrolcentersCerebrospinalfluidPonsMedullaoblongataCarotid arteriesAortaDiaphragmRib muscles20Figure 42.27 Automatic control of breathing

How are gases transported in the circulatory system?In many organisms, blood must transport large amounts of O2 and CO2Blood arriving in lungs -> low O2, high CO2 relative to air in alveoliIn the alveoli -> O2 diffuses into the blood and CO2 diffuses into the air.In tissue capillaries -> partial pressure gradients favor diffusion of O2 into the fluid around cells (interstitial fluid) and CO2 into the blood.

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Loading and unloading of respiratory gasesAlveolusPO2 = 100 mm HgPO2 = 40PO2 = 100PO2 = 100PO2 = 40CirculatorysystemBody tissuePO2 40 mm HgPCO2 46 mm HgBody tissuePCO2 = 46PCO2 = 40PCO2 = 40PCO2 = 46CirculatorysystemPCO2 = 40 mm HgAlveolus(b) Carbon dioxide(a) Oxygen22Figure 42.28 Loading and unloading of respiratory gases

What are respiratory pigments?Respiratory pigments -> proteins that transport oxygen Greatly increase the amount of oxygen blood can carryArthropods and many molluscs have hemocyanin -> copper = oxygen-binding component.Most vertebrates and some invertebrates use hemoglobin -> iron = oxygen-binding component contained within erythrocytes.

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings23How does hemoglobin work?1 hemoglobin carries 4 O2Hemoglobin dissociation curve -> shows that a small change in the partial pressure of oxygen can result in a large change in delivery of O2Bohr Shift -> CO2 produced during cellular respiration lowers blood pH and decreases the affinity of hemoglobin for O2Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings24

ChainsIronHeme ChainsHemoglobin25

Hemoglobin Dissociation Curves(37C)O2 unloadedto tissuesat restO2 unloadedto tissuesduring exercise10040020608004080100O2 saturation of hemoglobin (%)2060Tissues duringexerciseTissuesat restLungsPO2 (mm Hg)(a) PO2 and hemoglobin dissociation at pH 7.4O2 saturation of hemoglobin (%)400206080040801002060100PO2 (mm Hg)(b) pH and hemoglobin dissociationpH 7.4pH 7.2Hemoglobinretains lessO2 at lower pH(higher CO2concentration)26Figure 42.29 Dissociation curves for hemoglobin at 37C

How is carbon dioxide transported?Hemoglobin -> helps transport CO2 -> assists in bufferingCO2 diffuses into the blood & is transported either in blood plasma, bound to hemoglobin, or as bicarbonate ions (HCO3.)

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Carbon dioxide transport in the blood

Body tissueCO2 producedCO2 transportfrom tissuesCapillarywallInterstitial fluidPlasmawithin capillaryCO2CO2CO2RedbloodcellH2OH2CO3HbCarbonic acidHemoglobinpicks upCO2 and H+CO2 transportto lungsHCO3BicarbonateH++HemoglobinreleasesCO2 and H+To lungsHCO3

HCO3

HbH++HCO3

H2CO3H2OCO2CO2CO2CO2Alveolar space in lung28Figure 42.30 Carbon dioxide transport in the blood

How has gas exchange evolved?Evolutionary adaptations in gas exchange help animals do extraordinary things. Pronghorn Antelope -> runs extremely fast for long distances b/c of increased O2 consumptionDeep-diving air breathers -> stockpile O2 and deplete it slowly.Weddell seals -> high blood/ body volume ratio -> can store oxygen in their muscles in myoglobin proteins.

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SummaryInhaled airExhaled airAlveolarepithelial cellsLungs - Alveolar Air SpacesGAS EXCHANGECO2O2CO2O2Alveolarcapillaries oflungPulmonary veinsPulmonary arteriesSystemic veinsSystemic arteriesHeartSystemiccapillariesCO2O2CO2O2Body tissue - GAS EXCHANGE30What is cystic fibrosis?Genetic disease -> autosomal recessive Faulty gene for a protein that pumps Na+ in lung cellsCauses mucous buildup in respiratory tractSymptoms include: delayed growth, weight loss, fatigue, nausea, frequent pneumonia, coughing/sinus pressure due to mucousDiagnosed through blood test or sweat chloride testCurrently no cure, average lifespan 37 yearsTreated through specialized diet, frequent exercise, clearing mucous multiple times daily

What is bronchitis?Inflammation of the bronchi -> main air tubules to lungsCan be acute, i.e. due to viral infection, or chronicSymptoms include: cough, chest pain, shortness of breath, fatigue Treatment -> acute goes away on its own in 1 week -> chronic doesnt usually go away, but smoking cessation can help