anatomy lecture may 17 2011

8/4/2019 Anatomy Lecture May 17 2011

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DEVELOPMENTOF THE,CARDIOVASCULARSYSTEM

FORMATION AND EVOLUTION OF THE HEART TUBE-the development f the cardiovascularystembeginsearly. n the 3'dweek,with the

formation f theangiogenic lustersn the mesoderm;irst, hese lusters re ocated n

the ateral ides f theembryo. ut hey apidlyspreadn cephalic irection.brminga

horseshoe-shapedegionat the mostcranialportionof the embryo, he cardiogenic rea.

The angiogenic lusters f this areaacquire umenandfbrm a pairof endocardialeart

tubes.-initially, he cardiogenic rea s located entral o the prochordal late oropharyngeal

membrane),ver t being he cranial artof the ntraembryonicoelomic avity, vhich

developsater nto hepericardialavity;during he flexionof theembryo.2 mportant

eventsoccur:a).thecardiogenic reaand the prochordal late are rotatedabout 180"

alonga transversal xi s (because f the cephalocaudallexion, due to the rapid andextensivegrogh of the centralnervoussystem)-so the cardiogenic rea and the

pericarclialavitybecomeocated entrally ndcaudallyo theoropharyngeal embrane;

b).dueo the ateral lexion becausef theextensive rowthof the somites),he 2lateral

heart ubes omeclose o eachotherand fuse n a caudal irection.orminga single.

midline, ndocardialeart ube.-the endooardial eart tube grows into the pericardialcavity, carrying a layer of

splanchnic esodermvith t, layer vhich orms he epimyocardial antle; etweenhis

mantlean6 the endothelialube may be tbund,,br a time, a gelatinous ubstance,he

cardiacelly. Theepimyocardial antle ives ise o themyocardiumthemuscular all)

and to the epicardiumor visceral ericardium), hile the endothelialining the tube

tbrms heendocardirn .- initially, he endocardial eart ube s suspendedn the pericardial avity by u dorsal

mesocardium,hich disappearsoonafter brmation, ue o the furtherdevelopmentf

the heart a ventralmesocardiums never ormed);so, he tuberemains ttachedo the

pericardialavityat tscranial ndcaudal oles.-theendocardialubehas3 regions,n a cranio-caudalequencehese egions eing:he

bulbus ordis, heventricle nd he atrium;only the bulbus ordisand heventricle re

inside he pericardial avity,while the atrial portion s locatedoutside he pericardial

cavity, n themesenchymef theseptunrransversumtheprimordium f thediaphragm).

The ubehas2 largebifurcations t ts cranial r arterial ndcaudal r venous oles:

a) . he cranialbifurcationormsa pairof aorticarches, hich convey he blood rom he

heart.hroughhe pharyngealrches. rrdup to thedorsal ortaeha tdrain he blood ntotheumbilical rteries;

b). thecaudalbifurcationormsa sinus enosus ith a left and ight horn,which receive

the blood rom the vitell ine'umbilical nd common ardinal eins- he vitell ine eins

drain he yolk sac, he umbilical einsdrain he placenta,he common ardinal eins

drain the blood of the embryo hrough he anteriorand posterior ardinalveins(the

anterior ardinal einsdrain he body, cranial o the heart.while the posterior ardinal

veinsdrain hebodycar"rdalo theheart)



SUBDIVISIONS OF THE PRIMITIVE HEART AND THEIR

EVOLUTION-initially.

t theendof the 3'dweekof development,he heart s a straightube,which

growth apidly nside hepericardialavity;since t is fixedat both, oles. hegrowth n

i-engthesults-inbrmation f theheart oop(in themiddleof the4'r'week).This oop s

initially U-shaped, ith its convexside directed orwardand to the right; as growth

continues. he heart loop becomesS-shaped- ow, the primitive atrium becomes

incorporatednto he pericardial avity, osing ts attachmento the septumransversum;

it growsdorsallyand to the left, while the ventricle nd bulbuscordisare growing

ventrally nd o theright,betweenhem ormingan external ulboventricularulcus. he

bulbuscordis s narrow,except ts proximal hird. which is incorporatednto the

ventricle. iving rise -rnallyo the rabeculatedar tof therightventricle; o. he.function

betweenhebulbus ordis nd heventricle. xternallyndicated y the bulboventricular

sulcus,s the primary nterventricularoramen. he middle hird of the bulbus ordis.

knownas conus ordis,will form the outflow ractsof bothventricles, hile its distal

third, he runcus rteriosus, il l tbrm herootsand he proximalportions f theaortaand

of thepulmonaryrunk.-so.*hile the cardiac oop s formed, ocalexpansionsecome isible hroughouthe

lengthof the ube, n thedirectionn rvhich he blood lorvs hrough he primitiveheart.

these tructures eing:a) . the left andright hornsof sinusvenosus, achof thesehorns

receiving lood rom 3 important eins: itell ine, mbilical ndcommon ardinal eins;

b) . the sinusvenosus- small ransverseortion, he communicationetweent and he

primitive triumbeing he sinuatrial rifice; ). heprimitive trium- hecommunication

betweent and heventricles a narrow trioventricularanal; ).the rimitive entricle-

with the narrowprimary interventricular oratnen. which corresponds o the

bulboventricularulcuse). the conuscordis;1) . he truncusarteriosus;). the aorticsac

with theaorticarches-in the ?ndmonthof development,he ef t hornof the sinus enosusosests mportance,

becausef the obliteration f theveins hatopen nto hishorn first, he eft umbilical

vein, then he left vitell inevein and finally the left commoncardinal ein); all that

remains iom the left horn s the obliqueveinof the left atriumand lrecoronary it-tus.

Simultaneouslyith hedegenerationf the efthorn, he ighthornof thesinus enosus

gro\A/sonsiderablynd moves o the right sideof the body; t is gradually ncorporated

into the wall of the right atriumand the sinuatrial rifice moves iom the transversal

plane n a verticalplaneandbecomes longated. ightand ef t venous alvesborder his

orifice.The superior artso1'thesealves 'use nd brm a transient eptum purium; his

septum nd he nfcriorpartof the eft 'alve 'usewith the uture nteratrial eptum, ,hile

the nfbriorpartof the right valvegives ise o the valveof the nferiorvenacavaand o

thevalveof thecoronary inus.

SEPTUM FORMATION IN THE COMMON ATRIUM-at the end of the 4thweek. the septurnprimum grows from the roof of the primitive

atr ium downward. toward the endocardialcushionsof the atr ioventr icular anal; the

opening between these cushions and the lower border of the septum is the ostium

primum. r.vhichallows to the blood to pass iom the right atrium to the lefi atrium (the

right atrium receives oxygcnatcd blood from thc umbilical vein, by th e way of the



inferior vena cava,while the left atrium sends his blood to the {'etalsystemiccirculation

by the way of the left ventr ic le;.With furtherdevelopment.his passage ecomes mal ler

and smal lerand final ly closes,but smal l perforat ions ppear n the septumprimum and

they coalesce, iv ing rise, o the ostiurrr ecundum.ust before he closureof the ini t ial

orif ice. After the incorporationof the right horn of the sinus nt o th e right atrium. a ne w

fbld appears o the right of the septumprimum; this new fold is the septumsecunduman d

it grorvstowards the end<lcardial ushions,but it never f-usesvith them, at its inf-erior

border remainingan opening termed lbramen ovale. When the upper parl of the septum

primum graduallydisappears,he remerining art becomes he valve of the foramenovale.

The passagebetweenthe 2 atrial cavilies consistsof an oblique, elongatedclefi. The

septumprimum and the septumsecundum ogetherconstitute he interatrialseptum.

-befbre birth, th e blood pressure n the right atrium is&,,s-4,.'::'thann the left atrium,

because f the large volume of blood aniving tiom the placedta;after he blood enters he

right atrium, th e higher pressurepushes t through th e fbramen ovale an d through th e

ostium secundum nto the left atr ium. ,Afterbirth, the pressure n the right atr ium fal ls

becausehe umbil ical vein is closedoff, whi le the pressuren the left atr ium increases,

because he pulmonary veins are now rr:turninga largevolume of blood from the lungs.

So , th e on e way val ve of the interatrialseptum oses ts functional value; in the first f-ew

months after birth. th e septumprimum an d septum secundum use with one another o

fbrm a single,complete nteratrialsepturn.The remnantof the toramenovale is visible as

th e fbssaovalis.

Fateof sinoatrialstructures:-the right horn of the sinusvenosus brms the smoothportion of the right atrium(between

the ori f lces of the superiorand int-erior ena cava); the original primit ive r ight atr ium

{brms the rough. trabeculated ort ion of the defini t ive right atr ium; the dividing l ine

between hese2 potions s the crista erminal is-at first, into the left atrium opens the common trunk of the pulmonary veins; during

furtherdevelopment.he atrium enlargesand incorporateshis trunk, so that, f-inally.each

pulmonaryvein has it s own orifice; the incorporatedpart of the pulmonary veins fbrms

the smoothport ion of the left atr ium,whi lc thc original primit ive left atr ium persists s

the trabeculated ortion of the definitive left atrium

SEPTUMFORMATTOT{N ATRIOVENTRICULAR CANAL-at heendof the4thweek,? mesenchymalroliferationsnamedendocardialushions)

appear t the borders f the atrioventricularanaland heygrow owardoneanother nd

fuse. brminga septumntermediumhatdivides hecommon trioventricularanal nto

the eft andright atrioventric ularanals. fter the fusion, achatriventricularri f ice s

surrounded y local proliferationof ' mesenchymalissue.l-he

tissue ocatedon the

ventricular urface ecomes ollowedout and hinnedby the bloodstream;o, he valves

are fbrmedand hey remainattachedo the ventricularwall by the chordaeendinae f

thepapillarymuscles.

SEPTUM FORMATION IN THE COMMON VENTRICLE-by the end of the 4'r ' rveek. he 2 primit iveventr ic les egin o di lateand he medial .val ls

of the expandingventricles orm together he muscular nterventricular eptum: t grows

cranially. oward the endocardial ushionsand between he septuman d the f-used ar t of



the cushions emainsan interventricular rif ice, which is laterclosed by the membranous

i nterventricuar septum

SEPTT-IMFORMATIOI\ IN TI{E TRUNCUS ARTERIOSUIT ANT)CONUSCORDIS-during he 5thweek of development, pairsof opposing idgesappearn t he truncus

arleriosusrightsuperior nd eft inferior wellings r cushions) nd heygrow orvard

eachotherand use. brminga spiral eptum,he aorticopulmonaryeptum-hisseptum

divides heconus ordis nto heoutflow racts f theventricles nd he runcus rteriosus

into he aorticandpulmonary hannels. he primordia f the semilunar alvesbecome

visibleas small ubercles. t the base f these hannels; radually,hese ubercles re

hollowed ut at heirupper urf-ace,hr-rsbrming he semilunaralves.-in thesameime, he nterventricularoramen.oundabovehemuscularnterventricular

septum,s gradually losedby the menrbranousnterventriculareptum, ormedby the

prolif'erationf the caudalpartof the spiralaorticopulmonaryeptum nd of the cranial

partof theseptumntermedium.

CONGENITAL ANOMALIESa) . abnormalit ies in heart position- dextrocardia- is causedby the fbrmation of the cardiac loop to the left, instead o the

right; so. the heart s located n the right side of the thorax an d this abnormalitymay be

associated ith a total or partial situs nvcrsus transposition f the viscera)

b). abnormal i t iesof the atr ial septum

-arrial septal de.fbcts- he persistence of the interatrial foramen due to an excessive

resorption of the septum primum or to an inadequatedevelopment of the septumsecundum; hey causea left to right shunting of the blood, with increased lood flow

across he tr icuspidand pulmonaryvalves-commonatrium- complete 'ailureof septumprimum and septumsecundum o tbrm

c).abnormalit ies of the atrioventricular canal

-a single atrioventriculur orific'e- the endocardial cushions fail to fuse: in this

abnormal i ty,atr ial and ventr icularseptaldefectsare also found, because he cushions

part ic ipaten the closureof the ost ium primum and in the fbrmationof the membranous

interventr icular eptum;sometimes he endocardial ushions -use nly part ial ly,so only

the presence f the ostiumprimum may be found

-tricuspicJ tresia- obliteration of the right atrioventricular orif ice. associatedwith: a).

patencyof the tbramenovale, b). ventricular septaldefbct,c) . underdevelopment f theright ventricle,d) . hypertrophyof th e le{t ventricle.

d). abnormal i t iesof the ventr icular septum-thepersistence o./' he interventriculur orifice may be isolated, but also associatedwith

abnormalit ies n th e partit ion of the trunco-conal egion; is the caseof the tetrulopy o.f'

Fal lot, which combines4 anomalies: ). ventr icularseptaldefect (persistence f the

interventricular oramen); 2).pulmonarytrunk stenosis;3).overriding aorta-aortaarises

above he septaldefect. rom both ventricles;4).right ventricularhypertrophy-because f

th e higherpressure n the right side.



t .r .

( iI

I r : , tr r - r r . - . l , . ; . ,

{ :

-transpo.sitionof greal ve,ssel,v-he truncoconal septum fails to follow its normal course.descendingstraight downward, so the aorta originates from the right ventricle an d thepulmonary runk from the lelt

-per.sistentruncus arlerio.rzs- the truncoconal ridges fail to fuse and to descend owardthe ventr ic le, So, the undivided truncus receives blood fiom both ventr ic les. thepulmonary trunk originates fiom the common truncus and the interventricular septal

{efect is alwaysassociated.-$.abnormal i t ies of semilunar valves- he semilunar 'alves f the pulmonary runk or of

1 ' ,

theaortaare used or a variable istance-s thecase f thevalvular tenosis

anatomy lecture may 17 2011

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