RESPIRATORYPHYSIOLOGY

PhysiologyUnit4

InPhysiologyToday

Respiration• Externalrespiration

– ventilation– gasexchange

• Internalrespiration– cellularrespiration– gasexchange

• RespiratoryCycle– Inspiration

• Movingatmosphericairintothelungs

– Expiration• Movingairoutofthelungs

Lungsvs.Balloons

• Alungissimilartoaballooninthatitresistsstretch,tendingtocollapsealmosttotallyunlessheldinflatedbyapressuredifferencebetweenitsinsideandoutside

• Lungsand thechesthaveelasticproperties

LungCompliance

• Compliance– Elasticity– Tendencytorecoil– Tendencyofanelasticstructuretoopposestretchingordistortion

* Resistsdistension

• Surfacetension* Resistsdistension

- Surfactant• Reducessurfacetension• Increasescompliance(makesthemeasiertostretch)

AirwayResistanceF=ΔP/R

• Samevariablesthataffectresistanceinbloodvessels– Tubelength,tuberadius,friction– Tuberadiusmostimportantfactor

• Airwayresistanceissosmallthatsmallpressuredifferencesproducelargevolumesofairflow– Averageatmosphere-to-alveolipressuredifferenceis1mmHg,but500mLofairismoved(tidalvolume)

– Lowpressureandlowresistance• Pulmonary1/10thofsystemicvascularresistance

Ventilation

• Exchangeofairbetweenatmosphereandalveoli

• Atmosphericairpressureis760mmHgatsealevel

• Airmovesbybulkflow– F=ΔP/R– F=(Palv – Patm)/R

Boyle’sLaw

• Boyle’slaw=(P/V)• Pressureofagivenquantityofgasisinverselyproportionaltovolume

• Anincreaseinthevolumeofthecontainer(lungs)decreasesthepressureofthegas(air)

VentilationMechanics

• Lungvolumedependson:1. Transpulmonary

pressure(Ptp)• Insidetooutsideofthelung• Ptp =Palv – Pip• Theforcethatkeepsthelungsinflated• Transmuralpressure

– Acrossthewall

2. Howcompliantthelungsare

TransmuralPressures

WhatKeepstheLungsInflated?

• Elasticrecoilofthelungs* Atrestnaturaltendencyistocollapse

• LungsareheldopenbythepositivePtp– Atrestexactlyopposeselasticrecoil• Collapsingforceofthelungsis4mmHg• Intrapleuralpressureis-4mmHg

• Elasticrecoilofthechest* Atrestnaturaltendencyistoexpand

Pneumothorax

• ApierceinthechestwallallowsatmosphericairtorushincausingPiptogofrom-4mmHgto0mmHg

• Transpulmonarypressureactingtoholdthelungsopeniseliminated

• Lungcollapses• Chestwallexpands

Inspiration/Expiration

• Inorderforairtomoveinto thelungs,thepressureinthelungsmustdropbelowatmosphericpressure

• Patm >Palv

• Inorderforairtomoveoutofthelungs,thepressureinthelungsmustexceedatmosphericpressure

• Palv >Patm

TheRespiratoryCycle

PartialPressureofGases

• Dalton’sLaw– Pressureofeachgasisindependentofthepressureofothergases– Pressureofthegasisdirectlyproportionaltoitsconcentration– Individualgaspressuresinairistermedthepartialpressureofagas– Atmosphericair760mmHgatsealevel

• Airis78%nitrogen– 0.78×760mmHg=593mmHg– PN2 =593mmHg

• Airis21%oxygen– 0.21× 760mmHg=159mmHg– PO2 =159mmHg

– AltitudeandTemperaturealsoaffectpressure

PartialPressureofO2 andCO2 inBlood

TransportofO2 intheBlood

• 1Literofbloodcontains200mLofoxygen– Dissolvedinplasma– Boundtohemoglobin(Hb)

• SolubilityofO2 isrelativelylow– Only3mLofO2 candissolvein1LofbloodatarterialPO2 of100mmHg(2%)

– Remaining197mLofoxygenboundHb(98%)

TransportofO2 intheBlood• Hemoglobin

– Heme,globin– 280millionHbperRBCx4=

>1billionmoleculesofoxygenperRBC

• StatesofHb– Hb

• deoxyhemoglobin– O2 +Hb<--->HbO2

• Oxyhemoglobin

• Oxygencarrying-capacityofblood– apercent– AmountofHbO2 is80%oftotal

Hb,thesampleis80%saturated

Oxygen-Hemoglobin

DissociationCurve

• Sigmoidcurve– EachHbmoleculehas4sub-units

– Bindingcooperativity• BindingoffirstO2 increasestheaffinityforO2 atremainingthreehemeunits

• Significanceoftheshapeofthecurve– Steepslopebetween20-60mmHg• Increasedunloading

– Plateau• At60mmHg,90%saturation

• Oxygenreserve

ShiftsintheOxygen-HemoglobinDissociationCurve

• OtherfactorsinfluencethedegreeofHbsaturation– 2,3-diphosphoglycerate(DPG)– Temperature– pH– PCO2

• Ashifttotheright decreasestheaffinityofHbforO2– increasedunloadinginthetissues

• Ashifttotheleft increasestheaffinityofHbforO2– increasedloadinginthelungs

HbSaturationEffectsofDPGConcentration

• 2,3-diphosphoglycerate(DPG)– AlwaysproducedbyRBCs– IncreaseinDPGcausesashiftto

theright

• RBCsincreaseproductionofDPGwhenthereisadecreaseinPO2– Higheraltitude– Anemia– Transferfrommaternalbloodto

fetalHb

• IncreasedunloadinginthetissuestomaintainO2delivery

PO2 (mmHg)

HbSaturationEffectsofTemperature

• Highertemperatureintissuecapillarybloodthaninarterialblood

• Themoremetabolicallyactivethetissueis,thehigherthetemperaturewillbe

• Increasedunloadinginthetissue– ProvidesmoremetabolicallyactivecellswithmoreO2

PO2 (mmHg)

HbSaturationEffectsofpH

• Higher[H+]intissuecapillarybloodthaninarterialblood– ElevatedPCO2– Metabolicallyproducedacids

suchaslacticacid

• Themoremetabolicallyactivethetissueis,thegreaterthe[H+]– LowerpH– Higheracidity

• Increasedunloadinginthetissue– Providesmoremetabolically

activecellswithmoreO2

TransportofCO2 inBlood

• 200mLCO2/minproducedbymetabolism• 10%dissolvedinplasma• 30%ascarbaminohemoglobin(HbCO2)– CO2 +Hb<--->HbCO2

• 60%asbicarbonate(HCO3-)

– CO2 +H2O<--->H2CO3 <--->HCO3- +H+

– Carbonicanhydrase– PresentinRBCs

ChlorideShiftTissueLevel

• Bicarbonatereactionshiftstotheright...WHY??– CO2 +H2O<---> H2CO3 <---> HCO3

- +H+

• Steps:– CO2 diffusesoutofthetissuecellsintotheblood– CO2 movedintotheredbloodcells– CO2 combineswithH2OtoproduceH2CO3

• Carbonicanhydrasemakesthisreactionfast– H2CO3dissociatesproducingH+ +HCO3

-

– H+ bufferedbyhemoglobin,facilitatingtheoffloadingofO2

• FormsHHb– Cl- movesintotheRBCinexchangeforHCO3

- movingintoplasma– Bohreffect

• Increasedoxygenunloadingintissues• EnhancedtransportofCO2

ChlorideShiftTissueLevel

ReverseChlorideShiftPulmonaryCapillaries

• Equationshiftstotheleft.....WHY??– CO2 +H2O<--->H2CO3 <--->HCO3

- +H+

• Steps:– Hboxygenated– HbdecreaseinaffinityforH+

– ReversechlorideshiftasCl- movesintoplasmaandHCO3- movesinto

theRBC– H2CO3dissociatestoCO2 +H2O– CO2 expiredout

• Remember:– H+ isbufferedbyHbinRBC– HCO3

- goesintotheplasmaandbuffersincomingH+

ReverseChlorideShiftPulmonaryCapillaries

RespiratoryControlCentersRhythmicalBreathing

• Medullaoblongata– RespiratoryRhythmicity Center

• Controlsthediaphragmandintercostals

• Pons– ApneusticCenter

• Terminatesinspiration– PneumotaxicCenter

– Modulatesactivityofapneusticcenter– Smoothesthetransitionfrominspirationtoexpiration

• Cyclicinhibition

• Pulmonarystretchreceptors- Cutoffsignalforinspirationtoallowexpirationtooccur

ControlofVentilationMonitoringPO2,PCO2,H+

• Respiratoryrateandtidalvolumecanbealtered

• Peripheralchemoreceptors– AorticandCarotidbodies– ProvidesafferentinputtothemedullaviatheVagusNerve

– SensitivetoPO2• Centralchemoreceptors– IntheMedulla– HighlysensitivetoPCO2

ControlofVentilationMonitoringPO2,PCO2,H+

• Peripheralchemoreceptors– AorticandCarotidBodies– Sensitiveto:

• DecreasedPO2 (hypoxia)• IncreasedH+ duetothebuildupofotheracids(metabolicacidosis)

• IncreasedH+duetoCO2 retention(respiratoryacidosis)

• Centralchemoreceptors– Medulla– Sensitiveto

• IncreasedH+ inbrainextracellularfluid(CSF)– CO2 crossesbloodblainbarriertostimulatereceptors

ProtectiveReflexes

• Pulmonaryirritantreflexes– Reflexconstrictiontopreventparticulatesfromenteringlungs

– Receptorslocatedbetweenairwayepithelialcells– Coughreflex– Sneezereflex– Cessationofbreathingreflex

– Triggeredwhennoxiousagentsareinhaled– Chronicsmokingcauseslossofthisreflex