- - - --- --- ··-- - ·-. - -- ------- ·· ·-~; "': :; ,.._~

HUMAN .. EMBRYOLOGY

" . Dorsal uiew ·u .

''A.

1. Para xi a/ m~sod.

2. Intermediate ce.(l Tnass

3. :_ ateral .plafe

. ~ H\ tnt - e_wt.b r-~ <fVI ,'c-~t s 0 de.Al.1t-.

*"somatic

Cauih'e"i .

Pe~icardial ~auit!J~ ..J \ .. . .

leura/ cavit!f

. erifo,ea.l cauif~ . . . . - , _ ... -· ___ ..._ ____ -

FIG. 17.-Diagrams illustrating. the development o(- somites--

. . ' and intra•~mbryonic coelom ; , .

- ' ------,.­• ·:· · -c,i.~:,.. .. -

;:.

vi 11 i

Fig. 7-1. Longitudinal section of embryo showing the appearance of Glood isl:lllds in the splanchnic mesoderm of the wall of tlte yolk sac. Si1nilar islands are appearing in tlte body sdk. These wiq ultimately join and form, with the capillaries in the chorionic villi, the extra-embry-onic circulatioU.'· ·

. entoderm · · blood· islands

area vasculosa containing large nuuibers

· of blood islands

Fig. 7-2. Embryonic disc !'l.s seen from above. The amnion has been cut away and re­moved.

Fig. 7-3. Diflerentiation of mesodermal cells in a Glood island to form endothelial lining cells and blood cells.

·-"

. ;.. ... · .. :- ... ;

:··.

--·- =---- --. -- -'-·'-·

if \)2 . ..) \_ c:_.; .. ' ~ \"'\"'\\. ~

DEVELOPMENT OF C. V. S.

!~cad Snell chapter 7 page 81. ·Notice in particular the following:

l. The J.]jmitivc he_<!lLl!!IJc is formed by fusion -of a right ami lefl endocardial heart tubes. Differential growth ocfincs five segments of the heart lube which from caudal to cephalic QR according to directio-n -of blood flow arc:

2.

Sinus venosus-----~ primitive atrium _______ ..,. Primitive

ventricle' _____ ,. .. ~ ....

bulblis cordis. ( G6nus)

-----~ lruncu.s cu-te no sus

The .sill!J.S_y_G.nosus. t:eprcscnls the venous end of the heart. Ouc vitelline vein li'Olll the· yolk sac, Ot_re timbilical vein from lhc plct,Cenla and .9J.l.Q.

·.common cardinal vein from the body wall, joins ;;:ach horn of the sinus venosus.

® ® © @ Bulbur. cordio

I

,' ., ·' .. -.. .. -~-

·· · Vcntrlclo _

.. ·;enoouo "· -•·

. -:.~

Fig. 15.1 Fusion or cndlllhc\i;l\ hcnrlllthCs . ---~ - ·-

' ,· ..

__..- .... r

art~rles of pharynycal

vitelline vein

:->;-~~-truncus arteriosus

common cardinal vein

(distal part of bulbus cordis)

. The different parts of the endocardial heart tube within the. periardium. In the ~artiest stages, at;ium and the sinus venosus lie outsic.le the ericarc.lial c~vit . - .

1. Truncus arteriosus -+ forms-7 ascending aorta ~ pulmonary trunk .

2. Bulbus cordis (conus) EB Ventride~bulbo -ventricular chamber . ~ forms the trabeculated part of

It ventricle

3.

4.

5.

(Tt~

infundibulum of Rt. ventricle aortic vestibule of lt. ventricle trabeculated part of Rt. ventricle

A-V canal'-+ divided by the A-V (endocardial) cushions into Rt. & It. ~ A-V canals

the A-V( endocardial) cushions formSEPTUM INTERMEDIUM

Atrium-+ forms -7 rough- walled ant. part ofRt. atrium· ·mcluding its '\.auricle

lt. auricle

Smooth pa.rts of--7 Rt. atrium (formed by the Rt. hom of sinus venosus) ~ lt. atrium (formed by absorption of pulmonary

veins).

fc1Je. ~ k tUJ_ o.r ~ .J ~J ~ t.b.io cf.¥tlAJ

,. '< ) ' ..

~inni~ '¥-

. ~>M1'0.W.:. @

3. After formation of 1he head fold. the ~ lies dorsal to 1he .. _....,. .P..~'!!-.s~vi!Y and yentral to the for~be n~ginates

the pericardia! sac from the dorsal side: It is suspended from the dorsal wall of the pericardia! cavity by two layers of pericardium that cort;titute the ~al mesocardilJ!!l. This mesocardium soon disappears and the heart tube lies fre within the * peri£_ar~i!U.....l.£!C, suspended by its two ends (i.e. arterial and venous ends). HOwever, at this stage the caudal (venous) part of the heart tube (atrium * and sinus venosus) is embedded within the substance ofthe septum transversum.

.. ------------. C.lolcflll membrana

Tell fold

f ooegut Miduut

Amnlom

Porlc11dlum Yolk aac @. . . -~tri""' ft':l11SVVlJu.lll' .

Fts. 19. Mldsngollnl sect 1om or embyros at ~uccesslve Atnaes In head fold and tail fold formation , Note the cha.naeo In relative 110thlon of mldlloo structures. .

, . . , J.

Cardiogeni area

A1

P ricilrclial cav1ty

Amn1olic1;1,~ cav1ty . ' \

A1 81 H ilrl

be

J ' .

' .

7e:'~cardial 81 I(' cavity

Foregut

Dorsal

Connecting stalk

fn Cloacal membrane ~

figurc .12-2. Dr<1wings to show the· result of the rapid •r·owth of the· br.1in vesicles . on_J~~ili..o..D of the perica~~al. cavity and the deve oping earl tu e. nrtra itflc-·

card1ogenic areaJncftlie pericardiaTCavity are located in the front of the prochordal plate. As a result of the rotation along a transverse axis through the prochordal plate, the cardiogenic area (heart tube) finally comes to lie dorsal to the pericardia! cavity. A, 1 B days; B, 21 days; and C, 22 days.

lntraembryonic .

Endoderm

Intra­embryonic

coelom

Epimyocardial cells

Endocardial tube

figur<' 12-3. Sclwrn<rlic tr<rnsvC'rse sections through <'mbryos 01t cliff<'r<'nl sti1g<'s of dewlopnwnt, showing tlw form<ttion of ;1 singiC' lwart tubC' from p<rirt'd primordiJ. A, Early presomite embryo (<rpproximately 1 7 d<~ys). 8, L<~te presomite embryo (ap­proxim<ttely 1 n-ciax_s). C, At four somites (approximately 21 days). 0, At eight somites (<tpflroximately 27. d01ys). (Ad<tpted from sever<tl sources.)

, . . ,

(5) f'l

cnvi.ty

Ectod·crm

® ······------... :

( ~--------Foregut ...................... ~ <:::> 0-----.: ••• ·Hcnrt tubes

,--···.·,··~''' ··~ ,~,, __ .Splanchnopleuric . ...-Pcricnrdio.l .••• ..:~ ·.... mesoderm

Cl.lVity ::>-.-. _4,-i:; ·::: .. ~: ···· .. ·.·· '• ., ... :.·'·-: ... ;:; 1,<~·.:,,.. '·Somatopleuric

Po ric tal porico.rd:l.um · .,

Epicardium

.©

............ ;:·· ' ... ) .................

mesoderm

'\"" 'f I) t\5 V t'( S\!. ~ \ Vll.l.S J'b. rer:icl"lrdi(,\WV'. +

J~en e..rtt~e s

Fig. 15.~ !{clationship or hcnrl tubes to pcricnrdrnl cavity (A) Defore fo1ma1ion of head l"nld; (B) A.ftcr formation or head fol<.l, c nnd D show lhc JHOCCSS of invngination or lhc pericardia( cavity by the single hcnrllubc.

, . . , ,. I

*

The part of the heart tube lying ·within the pericardia! cavity is thus made up of bulbus cordis and ventricle. This part of the heart tube grows faster than the pericardia! cavity and as a result becomes folded on itself to form aU-shaped bulbo-ventricular loop. Subsequently, as the atrium and sinus venosus are ·freed from the septUm transversum; · they come to lie behind and above the ventricle and the heart tube is now S-sha~ At this stage the bulbus cordis and ventricle are separated by a deep bulbo-ventricular sukus.

This sulcus gradually becomes shallower so that the bulbus cordis and the ventricle come to form One chamber, which·communicates with the truncus arteriosus (arterial end of heart tube).

The atrial chamberld\ich lies behind the upper part of the ventricle and h·uncus arterio-sus EXPANDS so that parts of it come to project forwards on either side of the h·uncus. As a result of these changes the exterior of the heart assumes its definitive s 1ape. ~.........,.~......_/'......-"'--'"--~ . -- ..... ·- -

® i

Pericardial cavity I _!Jul·b_o-ven:.ricular aulcue

: Truncuo .orterionue ,' Ho l e in mcoo c ardium . .. .. ...... ' Atrium

®

Sinus Teooeue

© ®

Dulbo-ventriculor loop

Le !t atrium

·Lett Tentricl

Atrium Sinus venosus f'i~. 15.7 Estahlishmcnt of external form o f the heart .

@

Conuo

Ventricle

l'i[~. 1~5 'ichconcs tu , lo uw (" ) g_r:Hiooal frccins of heart tuhe fr~m scp_tum '""'""'""" ; (h) foltlint; uf locarttuhc; (c) <lis:'l'l'cardncc of mcsocnr<loum to lorm I he u:u1 svcrsc sinus uf pcrican.lium ,

, . . ,

\'. Tho..· 11\llbnvcntri~ular pnrlion uf the hcarl tube grows ITIUC11

1111111.! ~'"l'idly t lldll ullto..:r 1 cgiun~. but growth of the peri<.;ardial c:avit.v i.-. slow. The heart lul>t: bcnJs over itself, fonnin1; a

--~~ luop. , f T

liuH~I\L 1·11:'SEflHHY ~;":);~ \ / /~·· .· ;· .. , Vf-,'............_ ._e::· . ·····.·. c

____._-:;.:;:;; ---=t B~~ . ---~~ .. SV

~ ~~~ I'Ll< ll./\l<li 11\l. I... I\ v 1 ~-- .. _ _:__/ .

I· i ~~. I .L- J. 1'• i111itiv~.: hc.:an ~u~pc.:nJcJ in Lh;?pcricardial cavity.

']B:: But.BUS

;. · .. : i (: ! . .

. , . . ,

L•lt hOrn

Ant•rior cerd".nal vein

/ 7Rt · Yll•lllne vein --tt-:~~=~--___, ___ ......__, S.prum lransversum

oare_rlor eardfn.t vein

·\j ,.kf..~;n~ \JC-i Y1 • @

I

\ K41~ardl•c

channel

Azygos vein

Her>allc -~H--;-; I r tlnu~dl

-"'"-

®-_. -... ·r ~ --

IHK an4ttomoala

.A-Major venous channels or ·ao embryo at about 4 mm stnse. B-Porma­tion or in nom innte and iliac anaslamoses (arrows). Ductus venosus connects the left umbilical vein and right hepatocardiac channel. C. Rclfessloo of major vein, of left side.

,. '< .· ..

FATE OF THE SINUS VENOSUS

I. The sinus venosus develops lateral expansions called the right and left sinus horns. Each horn receives blood from the vitelline, umbilical, and common cardinal veins (Fig. 12-8).

II. Due to two left-to-right shunts of the blood, the ~ becomes larger than the left ho~, and consequently, tne st­noatnal openmg moves to the right and opens into the right primitive atrium. A. The first left-to-right. shunt of blood results from the

transformation of the vitelline and umbilical veins. 1. The caudal parts of the vitelline veins form the portal

vein. The parts passing through the liver become incor­porated into hepatic sinusoids. The cephalic part of the left vitelline vein disappears, whereas the cephalic part of the right vitelline vein forms the terminal portion of the inferior vena cava{~f''1fc ~clr<ic ci,fhnd)

2. The right umhilicnl vein nnd pnrt of the left umbilical vein between the liver and sinus venosus degenerate. · The remaining· part of the left umbilical vein carries all blood from the placenta and becomes connected to the inferior vena cava through the ductus venosus, which develops in the liver.

B. The second left-to-right s_hunt develops when the antedor

cardinal veins become interconnected by an .oblique anas­tomosis~ -{~ ·n.,. ~ Lt · /~r:n:_i. , ·cCifJ..~/c Cinnolw; .,..rtf e.) v~ fvJ

III. As a result of two left-to-right shunts of the blood, the left , umbilical vein obliterates, the left vitelline vein obliterates,

~1f· and finally the lcfl common cardinal vein obliterates. The left l]~rnJoses its importance and becomes smaller. Eventually~"$" distal part remains as the oblique vein of Marshall, while its proximal portion forms the€roru1ry-sinus)(LcroK ~ o t.~ \J ie wl)

IV. The right common cardinal vein and the rig'fit ahterior cardi­nal vein become the superior vena cava_

V. The right horn enlarges and receives all the blood through the superior and inferior venae cavae and finally becomes incor­porated as the smooth part of the wall of the right atrium.

VI. The@~tra-~ce or~·e-rightliorll_)~~Jadopts a slit-like configuration; and its margins form right and left venous valves (Fig. 12-5). · A. Dorsocranially, the valves fuse to form septum spurium. B. The left valve and septum spurium fuse with the develop­

ing atrial septum. C. A portion of the right valve divides to form the valve of

the inferior vena cava and the valve of the coronary sinus 1J.. G(l$tA term,'n·J . ./s J

, . . ,

®

®

-© ve.1.na

ProximAl ventral anao. ; , In!. vena

, Doreol anae • @ Splenic &. sup. . .

,•'meoenteric veins ... ....... ;. .... • ' I • • , <" ; ' ~ •

' ' '. Duodenum:. • • •

D~etol ven~rol anoo. •

Fig. 15.42 Dcvcloprilcnl of portal vein.

No{)(\ -{_~ ,L(-) r~'.fu.... {JoLJV\{).;t{Ay.. C-~ . ·- tt~ 'J?d1(-J-- vc. iA_ [Jf .. % t)--'- c"_AA!cJ p~uo {)_ G?Jd~_ y;_I-J} ·,~,_<t l.il./11'>) -~ -ti~· -l!.c_t-r- ' uw~.6;iic:J.. liLJ.n

b"~~"~··n•'•"'j <J'P-j~ t_n.c+cd JootA_~ ~J(J1)c} cfrcf\M t-{;~ fCtl(crrl"' welL( "f.Ct,., i nl-a ~ L. E Fr 6fa~,{~ db ft!\1~~ ve.i,,~ JvtcALV> ~woJtll~ rV d&J . /{tV\1\ c/Lt·~ f~· ~ ape~ 1 n+cJ d--t. . R1. IJ, k .tC 'r-1; vc_ un ~.£.~ 'C~ ~w..J' ·ct.t -J.eA..._.,.,,J_ PlL'-.1 ct 1"-tf/.t<ll. V<Jvl(l C~vtt).

- --- .

IMMEDIATELY AFTER BIRTH ~-CIRCULATORY CHANGES ·

l. The umbilical arteries (Fig. 12-9) constrict and later become the medial umbilical ligament. Proximal portions of these

J persist as superior vesical arteries. . 11. The umbilical veins and duct~ venosus no longer receive blood.

and become obliterated and remain as the ligamentum teres hepatis and ligamentlim vcnoSUf»-

111. With the expansion of the pulmonary capillary bed, the duc­tus arteriosus becomes constricted and later forms the liga­mentum arteriosum

l V. Wir h the corresponding increase in volume of returning blood in the left atrium, the pressure in the left atrium is increased, which causes tlic flap of the foramen ovale to close (Fig. 12-10).

, . . , J ,

Fate of sinus venosu~

The right hom of sinus venosus grows much more rapidly than the left the sinus opens on the · right side of the primitive atrium

Its opening becomes oriented in a vertical direction and its margins project into the right atrium as the right and left venous valves. The

~:;~~ :~~~: ~ese v~v~s- l~t~r fu~e -~o ~~~~~ p~o~e-~~~~e right hom ofsL:!~ venosus taken into and becomes the posterior smooth part of the right atrium-(posterior to crista tenninalis) The left venous valve • regresses and disappear. The right venous valve becomes the valve of the inferior vena cava and the valve· of coronary sin~s~1 : The left hom of sinus venosus ------t> remains small? (the left umb"\ical and vitelline veins disappear) and forms the coronaty sinus. <>J- (crist~ {eJLw..i "~.s)

® Body o! ainuj ····t.Urium TttDOBU8 .....

Ri.p:ht horn.: ~::·· - . . ·:.::_:;.\:;_· .. ~-e_rt born L .bt 1\ ... .-·.r··. -·Common ~ J A\ Jf\,:.· ___ _ cardinal v. ""\ H ~-

', r . Umbilical v. ~ 1 .1 ' • . · --- --{- vitellin• v.---? ~ o•S " f>r~~r ® .

;~~~::t0

e:&. ·····. ~eft horn and ebifte to right ' .::·: .';::· .. • its tributaries

:·:·: ·.:·:.:·.-. retrogreRe

.1(\(\hr. . . .© .· ..

Openi ng beco111e~ ~ narrow and ie --- --. Left horn ie now guarded b7 right ' , , _ •• a tributar)' o! :::.~:" ··~~ ~t~ ,,, .......

Fig. 15.8 Retrogression of lcrt horn of sinus venosus.

1Superior vena cava Coronary efnue

R.common. ® from R.common ® from L.horn of cardinal~:.. . . cardinal v.. . sinus venosuf! &· :

;f< -~ ' L.common cardinal R.horn of---~ L.common c~rdinal v. .,.._, .... -:;/.···· sinus venosus··- ---- · ' 4

·--~ j Sinu--atrial .... orifice gua~-d~d-/ by right and loft vonouo valvco

Hi gh t atrium

. L. horn of Sinus venous

~· .. ,,,..· 1fr~ni.,.,J fMf c-3 valve fused --;{· f, v. c /ri"W' "--.:::: to a t rial \ · f!.. vitc.ki~c V. septum

eoptum

, I

,

, I

I , , .

R.venoue valve forming cr~sta terminalie 1 . \J ...... \vt.r d1, I· v. c "" CcJYrt\-\1"t) Sci11<\S

~.,

Scheme illustrating incorporation of sinus venosus into right atrium. }~ ~. ·~ .... -.

Fate of the Atrio-ventricular (A-V) canal @ First rounded, then becomes transverse Two thickenings, the atrio-ventricular QR endocardial cushions appear on its dorsal and ventral walls. They grow towards each other and fuse

· forming the septum intermedium, thus dividing the canal into right and left halves.

N.B. Congenital malformation of the endocardial cushions is usually accompanied by anomalies of the tricuspid and mitral valves as well as atrial and ventricular septal defects.

R.venous valve

L.venous·· valve

@. R.valve greatly expanded

Inferior limbic band

Superior vena cava

Crista

(® ·coronary sinus

.. ._ ......

Superior ll.dlbic band .

© L.venous valve fused t9 atrial 'septu.m

inue Valve of coronary

•, sinus . ·.. ,. Inferior limbic band

. Inferior vena cava & its valve

Fate of the .right and left venous valves.

B Round atrio-venLri~ulai canol

I I

.I 'I

\ Ventral AV . cushion

Level of

® Canal becomes transverse .

®c=) Dorsal endocDrdinl cushion

© VentrDl endocardial cu8hion

@ ctSA.V.op•ning l ,/ Fus~d A. V. cuohionr. /

1

Right A.V. opening , I

SlngleAV canal'

/ AV septum

c

Right AV canal (tricuspid)

I

I I

Left AV canal / (bicuspid)

section C i \

septun

I

Fonnation ofthe interatrial sepum (page 87 Snell) d&twu;; ~cl7rt./; '3lth rJ3) .. rLJ s - tl e.v~..:....y V1A£ 11 f ~: .

SD~tum primum }!:- sickle-shaped and extends from the roof down to and fusing with the endocardial cushions (se tum intermediwn). Its upper part breaks down to form the foramen secundum oSfic<~V\ Secu11Jr-tw.)

Septum secundum ----P~,_ to the right of the septum primwn but does not reac~ the endocardial cushions leaving a valvular opening between it and the septum pnmwn .,...._ foramen ovale ( persists throughout foetal life).

After birth ~....__ left atrium begins to receive blood from the lungs )-- the pretsme inside it becomes greater than that in the right atrium the upper edge of septum primwn pressess against the septum secundum fuus closing the foramen ovale.(The lower edge of the septum secundum is thick and firm. In contrast, the edge of the septum primum that forms the lower boundary of the foramen secundum is thin and mobile like a flap. When blood tends to flow from the right to the left atrium, this thin flap moves away and there is no obstruction to blood flow. However, when there is a tendency for blood to flow from left to right this flap comes into apposition with the septum secundum and closes the opeining.

Septum apurium Septum primum Opening of

········~~~~--:::.~~-·~·· &~··~~...__......;:::::;:::s:=::;~-· pulmonary v.

Common a trial ·. chamber ••••• .

Septum •••••• . secundum

Septum pr:.mum to A.V.

A.V ~~shions

atrium

••• Right atrium

_ Formation of interatrial septum. The arrows in •p• indicate the path of blootl through the foramen ovate. . ·

ot,L' IJP. t· ior vena cava

foramen ovale

septum primum ( V·ll ve of foramen ova 1 e)

v ,1 \v~ ; nf infrri or v c r1.l C: i\Vi\

inferior vena cava

The oxygenated fetal blood, on reaching the for:~ men · ovale, is divided into two streams by tl:_Qsta div~@ which is the lower margin of the septum secundum . . The grea~t:r volume of hlo<iilenters the lcCLi.&iurn nnd the remainder, joined by venom hlrxid r ro~n the superior vena cava :~nd coron:~ry sit1us, passes from the right :11rwrn into the right~le.

After birth

superior vem: cDva

inferior vena cava

annulus ovalis represents lower free edge of the secundum

septum

{1

/ ~ u r '' b ) fossa ovalis

~----_,. represents the septum primum

~\.

tO~,;.;i<" '

from what has been said above it IS evident that the .right atrium is derived from

a) right half of the primitive atrium (rough ant. part) b) right hom of sinus venosus (smooth post. part)

The left atrium is derived from

a) left half of the primitive atrium b) absorped proximal parts of the pulmonary veins. (smooth post.

part).

------·-v:-· . ~

- Pulmon~try vein

• Le f t s t r 1 u m ~- . .

-~ *I ,-·Wall oJ atrium derive-1

!® . ostium secundum

~\ . · ,'/ / J_, from· abeorbed vein ? ~ ~.pulmonory vein

L.pulmonsry veine

© .i~ '\...._ _ _..../ {/-,:/ ~ )

Ahsorption of pulmonary vein' into left at(iu~l. foramen ovale

Fig. 2.12. Division of the common atrium. The anterior wall of the atrium has been removed to show the development of the septum. In F, the flow of blood through the foramen ovale is shown.

, . . , ,.

Separation of the Two Ventricles 1- At this stage the bult>'us cordis(conus), and ventricle, are separated by a

deep bulbo-ventricular sulcl!s .. This sulcus gradually becom~s shall~wer so that · the bulbus cordis (conus), and the ventricle, come to form one chamber, which communicates with the truncus arteriosus.

w 'Jt d.tve.lop .\1 2- The bulboventricular chamber~ into right and left ventricles by

the development ofthree structures: ' A- Ventricular septum. B- Extension from the atrioventricular endocardial cushions (septum

intermedium) . C- Proximalbulbarseptum(bu(bt1r ric0es 01 CaltH t>wU1•.-tj5)

3- The ventricular septum begins its development as a projection from the base or the inferior wall of the ventricle. As it enlarges, the septum forms two horns which reach up to the corresponding a-v endocardial cushions. The upper crescentic border of the septum bounds a temporary connection between the two ventricles called the

. --~terVentrlculartorame"ii) The ven~cular septum form the JII.UScular part of the interventricular septum (septum musculare ).

4- At the end of the seventh week, a downward extension occurs from the right margins of the a-v endocardial cushions (septum intermedium) to close the interventricular foramen. This extension forms the membranous part of the interventricular septum (septum membranaceum).

· 5- The proximal bulbar septum ·develops as two ridges which fuse together. This septum divides the bulbus cordis longitudinally into the infundibulum of the right ventricle d the vestibule of the left ventricle. ~shares in closing th mterventri~amen.

-:----~::....:..!..>-=-~ Mt ... J..faYf;<l"') (11Ar .:6 Truncus 0renin~_of atrium r.rterlosus

Ventricle

® ® © Fig. 15.(, S~.:hcmc to show inc11rporation of conus into the ventricle by disappear­ance of the hulno-vcntricular sulcus. Note thai the ~e gradually shirts to the centre of the po~tcrior wall of the-common bulbo-ventricular clt<lllll)cr.~

, . . , '•

<Jort;l

r Sri rfll nortopulmonary st>rt.um

(

Disl<'ll l.ndbnr septum 1- . 1' ~

~~ · l11Fundibululll of right \'Pntricle

~ r: -

Proximel bulbar seplum

~

Proliferation from A.V.cu~hicns . .

I)

2)

3)

' Inter ~~n t ri"cu 1 E1 r .soL v \ l.l.iYl

How the interventricular foramen is closed? By roliferation from: a. enoocardial cus 'ons (septum intermedium) b. proximal bulbar ridges (proximal bulbar septum) The proliferation from (a) and (b) will form the MEMBRANOUS PART of the interventricular septum which is divisible into an anterior part that separates the right and left ventricles and a posterior part that separates the left ventricle from the right atrium ">' thus called ATRIO-VENTRICULAR SEPTUM.

Which parts of the bulbo-ventricular chamber contribute to the formation of the Rt. ventricle? Both rough (trabeculated) part and smooth part (infundibulum) of Rt. ventricle are derived from the bulbus cordis (conus).

Which pajrts of the bulbo- ventricular chamber contribute to the formation of the It. ventricle? a. the rough (trabeculated) part is derived from the primitive

ventricle. b. the smooth part (aortic vestibule)

cordis (conus). is derived from the bulbus

, . ..

· ~ i-;-.. .. J ~;~

Distal Bulbar Septum

1-

2-

3-

4-

5-

Four endocardial cushio1;1s; anterior, posterior and two lateral are developed in the@@al\part ofthe bulbus cordis{ eon~s) A ridge is developed in the middle of each of the two lateral cushions. These two ridges fuse to form a complete septum called the distal bulbar septum. As a result, the distal part of the bulbus cordis is now divideJ into t~-Vo orifices: the pulmonary .orifice anteriorly and the aortic orifice posteriorly. Formation of the distal bulbar septum divides each of the lateral cushions into two. As a result, each of the pulmonary and aortic orifices is guarded by three cushions. The cushions form the pulmonary and aortic cusps. Originally, the cusps of the pulmonary valve are one anterior and two posterior. But, as a result of rotation of the vessels, two cusps become anterior and one posterior. Originally, the cusps of the aortic valve are two anter:ior and one poste~or. But, as a result of rotation of the vessels, one cusp becomes anterior and two·posterior.

re~·~. t opment o6 the d i. 6(a(_ &u Cba.t -!>Cptt~m

Pulf"'r~ 'lry vnlv!'

Dist.ol p'lrt of h6clbus r:ord i :1 ( (~fntAi)

~+-'~(nr!ocnrrliAl cushians

Right ;md left ridges

Rca.uange.~nt o6 the. cu ~p6 ('6 Ute

~OitM.IJ and at:~.tt.<c va(ve.~ due. f.IJ

~C'tllti.on t:~6 tlte. tll'O v~.M~e~

, . . ,

(Ao-rti~) Spiral Aoft~ulmonary Septum

. 1-

2-

3-

3

Two opposing ridges are developed in the wall of the truncus arteriosus during the_~ of development. The ridges have varying positions in the different parts of the truncus arteriosus. ~ In the lower part of the truncus, the ridges are right and left. As traced upwards to the middle of the truncus, the I<:t. ·. ridge becomes anterior; while the !'l.t ridge becomes posterior. In the upper part ofthe" tnincus~ .. the anterior ridge becomes left; while the posterior ridge becomes right. When the two ridges fuse together, a spiral septum is formed. This septum is called the aorticopulmonary or aortopulmonary septum. This septum divides the truncus arteriosus into the ascending aorta and pulmonary trunk.

aorticopulmonary sept..,

~ bulbar ridges A;:"" Pulmonary trunk

Ascending aorta

~·· ......,..··~- ~~ f\1-e~A.\':} ~ pulmonary trunk

?--aorta

Fig. 2.13. Formation of the aorta and pulmonar( trunk.

.. . ,

15

FOETAL CIRCULATION

Read snell page 105-107,"Notice the following:

a. In the foetus the right atrium receives two types ofblood (oxygenated and~).

- ,......._,-..

1. highly oxygenated blood from the placenta along umbilical-vein ductus venosus (inside liver ) Inf.

vena cava Rt. atrium.

2. deoxygenated blood comes from the upper part of the body (head & neck, brain and upper limbs, through the superior vena cava.

\ __ -~/ YE:RY LITT~~ MIXING .occurs betw~en tlw_~etw? typ¥~ ofblqo_d · mstde the Rt. atnum.

The oxygenated blood will pass from the right atrium ___ ___. left atrium (through foramen ovale) ___ ____.,.. .

It. ventricle Aorta Head, ----· neck, Brain, upper limbs.

passage of blood from Inf. vena cava ___ __.. Rt. atrium----~~ ( (

lleft;trium? ::J (1) he valve of the inferior vena cava directs the blood flow to the

'( (2) The pressure in the left atrium is much lower than tht~ pressure in r:::;'l the right atrium (No pulmonary circulation in the foetus). "-2J :) ~fu_..,. ?'rtM\A.'IA ,tn ~..1~ \J-'t\1'-(..

----:7- passage of deoxyrenated blood from sup. vena cava • Rt. atrium Rt. ventricle? The lower border of the septum secundum hangs over the foramen ovale & prevents blood from passing into the left atrium through the foramen ovale.

The deoxygenated blood will pass through the following:-Sup. vena cava Rt. atrium .., Rt. ventricle

----1•~ Pulmonary trunk • ductus arteriosus ~ ------1•• distal part of arch of aorta------+ descending aorta ----1_.._ ___ _..., Internal iliac arteries .._ Umbilical anteries -----•• ----1;.,.Placenta. .,.. 5'6/. ....-

Ou.cfliS arle!iasus

~ upcnor UE.na Cava

'I ll.m J,,f,c<d

Vt!/11

!'--\.; x i V\ j _c,?:, rQ q (c_ ?_ .,.

(jJ c'-.t

G ctt­C!) cvt­@~

clv..Qv.s VC-t1 o h( 5 ->

' . ' c 6. ~~· S<Liu r;lfc/ vJ,;~ QL I•V•-?- 7•

R -1 • ct tv ,. VI L.v..

l t- . Ci\ fy i v..~ 6 (,' J.

( 1)

co~\Ml;ctWt ® · n J se.ptd d_l ~t.ls.....,. A .s .J::>~ q

Anomalies of the atrial septum~ ntr't' ~ f.k3' a. The septum primum may fail to reach the atrioventricular

endocardial cushions, so that the form;en primum persists. This osteum primum defect may be associated with defects of the endocardial cushions.

b. The septum secundum may fail to develop so that the foramen secundum remains wide open ( osteum secundum defect).

c. The septum primum and secundum may develop normally but the oblique valvular passage between them may remain patent (patent" foramen ovale ).

®

<)

Complete filure of the septum primum and septum secundum to develop one atrium and two ventricles (.a_ trilocular biventricular heart). Interventricular septal defects may be seen either in the membranous or the muscular part of the septum. (More in the. membranous, why??). .· Persistent common atrio-ventricular (A-V) canal (results from complete failure of fusion of the anterior and posterior endocardial cushions which normally divide the A-V canal into right and left orifices (usually associated 'Vith defects of the atrial or :ventricular septa, why??) . ..-,- us\}..~ %.\), ~td . wid_ . Sef~(~ _ ctq{ Lls ~- occ ~~ --~- ;z o·l" 1>-~~<M~I J.s

® © @

Fig. 15.23 . Septal defects. A. Septum prirnurn defect. B. Septum secundum defect. C. Patent foramen ovale. D. Jnterven~ricular septum defect( . · .

Endocardial cushion dcrect . .t- • rrA ~ i -He..vvt

A-v C•\"'J

CDIIHON ATRIUM

C011110H VENTR 1 CLE

septum secundum .1$· , '·;:1:@/·.~::.<i •. ~l .. · ~' , • I ' t • :

. . ... 'V\.ot"AA4 . . . ' I:, . ' ' : . I ' • I ~ ' 0 : •

ovale ' .. ! ' ' : ----..----~------...:___,_, _!,._ ,_, __ ,!.._ .. _ . _ _ .

' Almormalitics of the truncus nnd conus A. Unequal division of the truncus arteriosus results in tetra:

logy of Fallot which consists of the following defects: 1. Pulmonary stenosis (smaller division) · 2. Overriding aorta (larger division) 3. VSD (membranous part fails to develop) 4. Hypertrophy of right ventricle (Fig. 12-13)

'~Ji ·· . • : . . . · ... . . . ..

pulmonary stenosfs

Atrtal Septal Defect A

displaced aortfc

Persistent Truncus Artertosus.

c

. , .... .. .

• •• 0 .·.! . :. •· •,

hypertrophy of rtght ventricle ··:·

; ~ trunk . '' ' ..

. !

· ventricular septal defect

·'i.

: ,.·;' .· i ! l'; ! I I '•

; ;'(: .\ .: .

~- -·---: Persistence of truncus arteriosus 1·

This results from failure of truncoconal ridges to fuse (failure of the formation of aorticopulmonary ~eptum) I i,: Fig. 12-14). · .. ·· ·: Complete transposition of the great vessels I ; 1. The aorticopulmonary....s~ptum (truncoconal .septum) f· .::

fails to follow the normal spiral course. I ' 1

2. The pulmonary trunk arises from the left ventricle and ' the aorta arises from the right ventricle (Fig 12-14). . i

3. This condition is incompatible with life unless it is associated with a septal defect or a patent du~tus arte- : riosus .

. ·'-

( 1 j

l'dlonl lorumon

ovale -----tP:__--~

(.2·.~ 0n3lA .h ~ j ..,. !,-?' "'~4.

Interventricular ) soptol dofoct

Q) (•1)

Undordovolopod nghl vontriclo ----.!11'---- Overdeveloped

loft vonlricle

Figure S-0. Trrcu:;p1u atro:>tJ, 111u1catrng tllu four mnrn cnrdrac defects assocrntcd wrth tl1i~ malfornntron .

c. Tricuspid atresia iFig-urc G-91 -is obliteration of t.hc right AV canal. -is ch:u:nclerizccl b~· nbscncc of t.hc tricuspid v;tiVL'.

-Is associated clinically \~'ilh marked cyanosis. -is :1.hv;-tys nccompanicd by the follnwin:.::-: (1) Patent foramen ovale (2) IV septum dcfcc~ (:3) o,~cnlevelopcd left ve.ntt·icle (•1) Underdeveloped right. ventricle

L--~~ Patent

Tr<tnspo:>ilion of Grc~;~t Vessels Pulrnon<~ry Valvular Atresia

ov~l

foramen

Figure 12-JO. t\, Tr.1nspo~.ition of the grc,lt vessels. l3, Pulmonary Jtresia with norm.1l ,wrtic root. The onl~· acce~s r•)ule to the lungs is by woy of the p.1tent ductus , I r( L'f'i ( 1\ll..,.

A. Coarctation of the aorta ·• A narrowing of the aorta either just above or below the

ductus arteriosus (Fig. 12-16). I. Preductal coarctation

a) Generally associated with other serious congenital heart defects

b) Prenatal circulation of blood is not seriously dis­turbe~ b~cause most of the blood from the right ventncle IS shunted through the ductus arteriosus which is distal to the narrowi~g of the aorta. '

c) ~fter b~rth this major shunt is closed, the pressure m the d1stal aorta remains low, and the blood flow to the body is impeded.

d) Usually fatal in infancy.

tlunMI\l l'ur.IHKTM. CIJARCTI\TION POSTDUCTAL COARCTATION

t "IR.12-Ilo . ("on•~lnllnnnfthcnnrln.

2. l'ostductal coarctation a) The narrowing of the aorta is distal-to the ductus

b)

'~c)

arlcriosus . . ~>rena tal blood circulation ·thro.ugh the aorta is_ im­peded. A collateral circulation becomes established during fetal life which shunts the blood around the coarcta-tion.

d) As the collateral circulation is already well estab­lished, after birth no significant change occurs in the circull\tion.

' c) This is the common finding In cases of Thrncr's syndrome.

B. Patent ductus arteriosus This condition may occur as an isoltacd abnormality or

in combination with other heart defects. It is more com­mon in females than in males. It is also the most common / cardiac mal formation associated with maternal rubcUaJ::"

/

l .

-:J i~~!!-~_t,i.9n._<!~rin~l!I!.Y...Jlt>g!J.~.n~y. Superior vena cava

VI. Abnormalities in the positioning of the heart A. Dextrocardia (displacement of the heart to f he right)

The heart tube bends to the left instead of the right, so the heart and the great vessels are reversed; otherwise, the heart functions normally. This is usually associated with ~itus inversus. Isolated dextrocardia usually results in

f IA-e_ 1\·1 GY1 i\.r j ·-~./"-./

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