RESPIRATORY PHYSIOLOGY Physiology Unit 4
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