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.

�

�

�

�

�

�

�

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.