ANHB1102: CARDIOVASCULAR SYSTEM THE HEART AND BLOOD VESSELS
Transcript of ANHB1102: CARDIOVASCULAR SYSTEM THE HEART AND BLOOD VESSELS
ANHB1102:CARDIOVASCULARSYSTEM
THEHEARTANDBLOODVESSELS
DEVELOPMENTOFTHEHEART(EMBRYOLOGY)
- Allinvertebratesandchordateshaveaheart.
- TheheartfuncNonsasapumptoovercomeimpossiblylongdiffusiondistances.
• ItpumpsfromregionsofhighoxygentensionandnutrientconcentraNontotheallthecellsinthebody.
- First3weeks:fetusistoobigfordiffusiontowork.• Thefluidfilledspaceintheblastocystkeepsthecellscloseenoughtocellswithnutrientsandoxygen.
- Day19:embryobecomesaflatdisk(withaheadendandatailend).
• Heartdevelopsinthecardiogenicarea.• Bloodvesselsformthroughvasculogenesisaroundthecariogenicregion.
• Heartformsasanendocardialtube;2tubesoneithersideofcardiogenicarea(fusetogetheratday20).- Day22:tubularheartformsandtheheartstartsbeaNng.
- Day23:developsfurtherwithavenousend(incoming)andanarterialend(outgoing).
- Day28:thehearthaselongatedandfoldedwithbothvenousandarterialendsbothatthetop.- Last4weeks:valvesformandthechambersgetdivided.
- Birth:thecirculaNontothelungsandbodyisseparated.
ANATOMY
- Loca=on:betweenlungs,thesternumandthoracicvertebra;surroundedbyribsinaspacecalledmedias=num.
- Theheartsitsinadensefibrousconnec=ve=ssuebagcalledthepericardialsac;itdiffuseswiththebasesofthegreatvessels.• Theheartbulgesbecauseitwaswellfixedinthissac.
• Thebo\omofpericardiumisfusedtothediaphragm.
- TheheartgrowsintoaspacecalledthepericardialcavitywhichisobliteratedaEerinvagina=on(oncetheheartenters).
- Asheartgrows,itsouterliningfuseswiththeserouslayer(secretesa
fluidtoallowthehearttomovefreely)ofpericardium.
- Vesselsandtheheartislinedwithsimplesquamousepithelium.
PERICARDIUM
- Pericardiumisadoublewalledsacenclosingtheheart.Itisanchoredtothediaphragm.
• Fibrouspericardium(denseirregularconnecNveNssue):limitsover-fillingoftheheart.
• Serouspericardium:
⟶ Parietalserouslinesthefibroussac.
⟶ Visceralserous(epicardium)coversthesurfaceoftheheart.
- Fibrouspericardium>serouspericardium>parietalpericardium>visceralpericardium(conNnuous
withtheepicardium)>myocardium>endocardium.
CORONARYVESSELS
- Theveryfirstbranchesthatcomeoffthebaseofthe
aortaarethele_andrightcoronaryarteries.Theyrun
aroundintheatrioventricularsulcus.
• LeEcoronaryarterygivesrisetotheanteriorinterventricularbranch.
• Rightcoronaryarterygivesrisetotheposteriorinterventricularbranch.
- Thecoronarysinusentersthecoronarysulcusandemp=esintotherightatrium.Thesebloodvessel
branchessupplyanddraintheheart.
ANHB1102:CARDIOVASCULARSYSTEM
EXTERNALFEATURESOFTHEHEART
- Thepulmonarytrunkisacommonvesselleavingthele_ventriclewhichsplitsintorightandleEpulmonaryarteriesandthe4pulmonaryveinswhicharecomingbackfromthelungs(openintothele_atrium).
- Thehearthas4chambers;le_andrightatriumandle_andrightventricles.
- TheleEventriclehasathickermuscleasitpumpsbloodtotherestofthebodybuttherightventricleonlypumpsblood
aroundtheheart.
- Betweentheatriaandtheventricles(formmostofthesubstanceoftheheart)istheatrioventricularsulcus(coronarysulcus)whichisagroovefilledwithfatthatrunsallthewayroundtheheart.
- Betweentherightandle_ventriclesthereisaposteriorinterventricularsulcus.- Inferiorandsuperiorvenacavaenterintotherightatrium.
- Theblooddrainsfromtheheartviathecoronarysinus(opensintotherightatrium).
INTERNALFEATURESOFTHEHEART
- Betweeneachatriumandventriclethereisanatrioventricularvalvewhichhaveflaps.• Whentheventriclecontracts,ittriestoforcethevalveflap.
• Papillarymusclescontracttoputtensiononchordaetendinaetopreventflapsfromturninginsideout
duringventricularcontracNon.
• Thepulmonarytrunkandpulmonarysemilunarvalvesarisefromtherightventricleandcloseunder
thepressureofblood.
• Thebloodtriestoflowbackwhentheheartrelaxes.- VesselsclosetotheheartareelasNc.Whentheheart
contractstheycanexpandandwhentheheartrelaxes,
theelasNcrecoiltriestosqueezethebloodbackintothe
heart,thevalvescloseandthebloodispassedon.
HEARTSKELETON
- Densefibrousconnec=ve=ssuewithsomefibrocar=lage.- Givesabasisforeachofthevalves.Pressurestopsthemfromspreading.- Providesananchorfortheheartmuscle.Theheartmuscle,fromhavingbeinga\ached
tothefibrousskeleton,spiralsoffaroundtheheart.Sowhenthemusclecontracts,ithas
awringingacNon.
- Theringshapeiseffec=veatsqueezingbloodoutoftheheart.- ItprovideselectricalinsulaNon(delaybetweencontracNons).
ANHB1102:CARDIOVASCULARSYSTEM
BLOODVESSELS
- Arteriescarrybloodawayfromtheheart.Veinscarrybloodtowardsit.- Bloodvesselsasawholehaveastandardstructure.Theyhave3tunics:
• Tunicainterna:alwayshasalayerofendothelium.MayalsohaveconnecNveNssueandelasNn.
• Tunicamedia:hassmoothmuscle,collagenandvariableamountofelasNcNssue(thickerinarteries).
• Tunicaexterna(advenNNa):connecNveNssueandcollagenfibres(thickerinveins).
THECARDIACCYCLE
BASICPLAN
- Theheartconsistsoftwopumpsinwhichbloodflowsinasingledirec=onduetothevalvesinthepumps.
• Firstpumprepresentsbloodgoingtoacapillarybedin
thebodywheregasexchangetakesplace.
• Deoxygenatedbloodisbroughtbacktothesecondpump
whichpumpsviaarteriestocapillaries.The
deoxygenatedbloodthenreturnstothefirstpump.
• Thevolumeisthesameinbothpumpsinthecircuit.• Eachpumphasasmallatrium(smallwiththinnerwalls)
andalargeventricle(largerwiththickerwalls).
• Le_ventriclepushesbloodtothebody.
• Pathwayofbloodintheheart:rightatrium>rightventricle>pulmonarytrunk>branchesintopulmonaryarteries(to
lungs)>pulmonarybeings(comingbackintotheheart)>le_atria>le_ventricle>outofaorta.
- Systolicbloodpressureis120mmHganddiastolicis80mmHg.
Arteries(averagepressureisupto120mmM)
Veins(averagepressureisupto10mmM)
ConducNnglargearteries:
- Thickwallvesselsneartotheheart.
- Theymaintainbloodflowandsmoothoutbloodpressure.
- ThickelasNcwallabsorbspressurefromcontrac=onsoftheheartbystretching.
- Whentheheartrelaxes,theelasNcrecoil
pushesthebloodon.
Largeveins:
- So_wallwithlargerlumen.- Contain64%ofbloodvolumeatrest.
- Mediaisthinnerwithsmoothmuscle.
- Externaisthickerthanofthelargeartery.
- Havesomemuscleinexternaandmedia
allowingcontracNoninlengthandwidth.
- Example:venacava,renalveinsetc.
DistribuNngmusculararteries:
- Smallervesselscanchangediameter.
- UnderautonomicNScontrol(vasomotor).
- Maintainbloodpressure.
- Deliverbloodtotheorgans.- HavelesselasNcfibres.Instead,theyhave
internalandexternalelasNclamina.
Mediumveins:
- Havesomesub-endothelialNssue.
- Mediahassomemuscle.
- Externaisthickerthanthemediumartery.
- Veinsarepairedarounddeepbloodvessels.
- Endotheliumformsflaps(valves)whichincreasebloodflowbacktotheheart.
Resistancesmallarteries:
- Maycontrolflowintocapillaries.- Cancontractabypassandreducetheamountofbloodthatsgoingintoa
capillaryinaparNculararea.
Venules(smallmuscularveins):
- Somehavemuscles,othersareendothelium.
- Similartocapillaries.
- Theyareveryleakywherealotoffluidcanleakoutofthepost-capillaryvenules.
Capillaries
- Capillariesjoinarteriesandveins.ItiswheretheexchangebetweentheNssuesoccurs.- Endotheliumandbasementmembrane.
- Canbecon=nuouswithNghtjuncNons(foundeverywhere),fenestratedwithwindows(foundinthekidneys)orsinusoidalwithlargeholes(foundintheliverandspleen).
- EndothelialcellsarewrappedaroundandhavespecialisedjuncNonsbetweenthem.
- Thinwallsallowrapidgasexchange.
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ANHB1102:CARDIOVASCULARSYSTEM
CONTROLOFTHEHEART
CARDIACMUSCLE
- Cardiacmuscleisinvoluntary.Ithaslargeamountsofmitochondria.- Themusclecellstendtobranch.Eachcellhasasinglenucleus.ThecellsarejoinedbyintercalateddiscsthatconsistofdesmosomesandgapjuncNons
(allowselectricalconducNon).
- Cardiacmusclecellsdonotneeds=mula=onforcontrac=on,itworksassingleunit.Thecellshavealongerrefractoryperiod.
- TheheartisverysensiNvetochangeinextracellularfluidconcentraNons.
- Allcardiaccellshaveanunstablemembranepoten=al.TheyareleakyintermsofK+concentraNonwhichallowsinsideof
celltobecomemoreposiNvetocarryacNonpotenNals.
- SpecialisedautorhythmiccellsformthecardiacconducNonsystemwhichhavelosttheabilitytocontract.
- Cardiaccellsundergospontaneousdepolarisa=onNllanacNonpotenNaloccurs.ThisiniNatescontrac=on.- Thethicknessofthecardiacmuscleintheventricleislargerinthatoftheatriumastheatriumonlyhastopassbloodthe
ventriclewhichneedsastrongerpumptopassthebloodtovalvesandthebody.
CardiacCycleTheheartcyclecostsofalternaNngperiodsofcontracNon(systole)andrelaxaNon(diastole).Ventricularpressure
determineswhenvalvesopen;AVvalvesopensinlowpressureandsemilunarvalvesopeninhighpressure.
VentricularDiastole
- Arteriolediastole:chambersarerelaxedandmostoftheventricularfillingoccurs(70-80%).VentricularpressureinlowerthanatrialpresssotheAVvalesopen.
- Arteriolesystole:theatriacontractsandpushesthelast20to30%ofblood.Eveniftheatriadoesnotcontract,theventricleshaveenoughbloodtopumparound.
Isovolumetric
ContracNon
(Systole)
- Ventriclescontract(tensioninthemuscles).
- VentricularpressurebeginstoriseaboveatrialpressurecausingAVvalvestoclosetopreventbloodflowingbackintotheatria.
- SemilunarvalvesremainclosedaspressureissNllnothighenough.- ContracNonoccurswithincreasingpressurebutthereisnobloodmovement.Thevolumeisconstantasallvalvesareclosed.
VentricularEjecNon
(Systole)
- VentricularpressurerisesenoughabovetheaorNcpressurecausingsemilunarvalvestoopen.
- Bloodtobeforcedoutbyventricularejec=on.
Isovolumetric
RelaxaNon
(Diastole)
- Theventriclerelaxeswherepressuredecreases.
- Somebloodpoursbackdownintothepulmonarytrunkclosingthesemilunarvalves.
- BloodthattriestoflowbackincausesAVvalves(cupshape)tofla\en.AVvalveswillremainclosedunNlventricularpressureislessthanatrialpressure.