Development of Heart- Seminar at JJMMC , Davangere.

1. By Dr Robin Thomas

2. By Dr Robin Thomas

3.  The vascular system appears in the middle of
3rd week , when embryo is no longer able to
satisfy its nutritional requirement .
 The Heart develops from splanchnopleuric
mesoderm related - intraembryonic coelom
that forms pericardial cavity. This mesoderm
called Cardiogenic area.

4. Cardiac development involves :
 1.Establishment of cardiogenic field
 2.Formation & position of heart tube
 3.Cardiac looping
 4.Cardiac septation

5.  Cardiac progenitor cells lie in the epiblast ,
lateral to primitive streak.
 Migrate towards primitive streak
 Cells destined to form cranial segments of heart ,
outflow tract, migrate first & cells forming more
caudal portions , right ventricle,
left ventricle & sinus venosus migrate in
sequential order.
 Cells procede towards cranium & position
themselves rostral to buccopharyngeal
membrane & neural folds- reside in splanchnic
layer of lateral plate mesoderm.

6.  Cardiac progenitor cells lies – epiblast ,lateral
to primitive streak. Cells procede towards
cranium –rostral to buccopharyngeal
membrane & neural folds. Reside in
splanchnic layer of lateral plate mesoderm.

7.  Blood islands appear in this mesoderm –form
bloodcells & vessels –vasculogenesis.
 Blood islands unite & form horseshoe shaped
endothelial lined tube surrounded by
myoblasts- cardiogenic field – intraembryonic
cavity over it develops into pericardial cavity.

8.  Initially central portion of cardiogenic area is
anterior to buccopharyngeal membrane & neural
plate.
 Closure of neural tube & formation of brain
vesicles – central nervous system grows cephalad
 Buccopharyngeal membrane is pulled forward –
heart & pericardial cavity move first to cervical
region & finally to thorax.
 Embryo fold cephalocaudally & laterally- caudal
region of paired cardiac primordia merge.

9.  18 Days embryo 20 Days embryo
 Central portion- cardiogenic area anterior to
buccopharyngeal membrane & neural plate.

10.  21Days embryo 22 Days embryo
growth of brain & buccopharyngeal memb
cephalic folding of pulled forward –heart &
embryo. pericardial cavity moves
first to cervical region-
thorax.

11.  22 day embryo
 Embryo folds cephalocaudally & laterally-caudal
region of paired cardiac primordia merge-
 Heart –continuous expanded tube with inner
endothelial lining & outer myocardial layer. Pump
blood –first aortic arch –dorsal aorta.

12.  Heart - continuous expanded tube – inner
endothelial lining & outer myocardial layer.
 Receives venous drainage at caudal pole - pump
blood - first aortic arch into dorsal aorta .
 Heart tube - attached to pericardial cavity by
dorsal mesocardium.
 Dorsal mesocardium disappears-creates
transverse pericardial sinus-connects both sides
of pericardial cavity.
 Myocardium thickens & secrete thick layer of
extracellular matrix – rich in hyaluronic acid –
separates from endothelium.

13.  Mesothelial cells on surface of septum
transversum form proepicardium-later form
epicardium.
 Heart tube consists of 3 layers
Endocardium-internal endothelial lining
Myocardium-muscular wall
Epicardium-outside of heart tube

14.  Right & left endothelial
heart tubes.
 Fusion of heart tubes
from cranial to caudal
ends.

16.  Arterial end of heart tube Venous end of
heart tube

17.  Single endothelial heart tube shows series of
dilatations.
 1.Bulbus cordis
 2.ventricle
 3.atrium
 4.sinus venosus

18.  Ventricle & atrium are connected by
atrioventricular canal.
 Sinus venosus has prolongations - right & left
horns.
 Bulbus cordis lies at arterial end of heart tube
–divisible into proximal part - conus &
distal part - truncus arteriosus.
 Truncus arteriosus continuous distally with
aortic sac-continuous with right & left
pharyngeal arch arteries-continuous with
right & left dorsal aorta.

19.  Sinus venosus lies at venous end of heart-has
right & left horns.
 One vitelline vein (yolk sac), umbilical vein
(placenta), common cardinal vein (bodywall)
join each horn of sinus venosus.

20.  Heart tube elongate & bend on day 21.
 Cephalic portion bend ventrally,caudally & to
right.
 Atrial portion shift dorsocranially & to left.
 Bending creates cardiac loop-complete by
day 28.

21.  Cephalic portion heart tube bend ventrally,
caudally & to right.
 Atrial portion shift dorso-cranially & to left.
Creates Cardiac loop-complete by day 28.

23.  Dextrocardia-heart loops to left instead of
right.
 Heart lies on right side of thorax instead of
left.
 May coincide with situs inversus-complete
reversal of asymmetry in all organs.

25.  Truncus arteriosus form ascending aorta &
pulmonary trunk.
 Conus absorbed into ventricle & form
chamber –partitioned into right & left
ventricles.
 Primitive atrium partitioned into right & left
atria.
 Sinus venosus absorbed into right atrium.
 Right common cardinal vein forms superior
vena cava.

26.  Umbilical vein disappears.
 Right vitelline vein forms part of inferior vena
cava.
 Left horn of sinus venosus retrogresses-form
part of coronary sinus.

29.  Sinus venosus & primitive atrial chamber are
connected by a wide opening
 Opening becomes narrow-shifts to right-
narrow slit-right & left venous valves.
 Cranially 2 valves fuse to form septum
spurium.
 Atrioventricular canal divides into right & left
halves.
 2 thickenings-atrioventricular cushions
appear on dorsal & ventral walls.

30.  Atrio ventricular cushions grow towards each
other & fuse –form septum intermedium.

32.  Begins at day 26-ingrowth of large tissue
masses.
 Endocardial cushions at atrio ventricular &
conotruncal junctions.
 Endocardial cells de differentiate & form part of
atrio- ventricular valves.
 Complete septation of atrioventricular canal –
fusion of endocardial cushions.
 Most of atrioventricular valve tissue –derived
from ventricular myocardium –undermining of
ventricular walls.

33.  Physical separation of 2 valves (mitral &
tricuspid valve) produce atrioventricular
septum.
 Absence causes-Atrio ventricular canal
defects. (Endocardial cushion defects)

34.  1.Complete endocardial cushion defects
Ostium primum ASD, VSD in interventricular
septum, clefts in anterior mitral valve & septal
leaflet of tricuspid valve.
 2.Partial endocardial cushion defects
Ostium primum ASD, clefts in mitral &
tricuspid valve.

39.  Septation of atria begins at day 30 day .
 Atrial chamber undergoes division into right
& left halves-formation of 2 septa.
 Septum primum arises from roof of atrium ,
to right of septum spurium.
 Septum primum grows downwards & fuses
with atrioventricular cushions.
 Upper part of septum primum degenerates-
form foramen secundum.

40.  Septum secundum formed to right of septum
primum.
 Septum secundum grows downwards from
roof of atrial chamber-overlapps free edge of
septum primum.
 Blood now flows from left to right through
oblique cleft b/w 2 septa-foramen ovale.
 During fetal life oxygenated blood reaches
right atrium from placenta.
 Blood reaches left atrium tru foramen ovale.

41.  After birth left atrium receives oxygenated
blood from lungs- foramen ovale obliterated
by fusion of septum primum & septum
secundum.
 Annulus ovalis –septum secundum.
 Fossa ovalis-septum primum.

42. Inter atrial septal defects
 1.Septum primum defect
 2.Septum secundum defect
 3.Patent foramen ovale
 4.Premature closure of foramen ovale

44.  Right atrium derived from :
1.Right half of primitive atrium-main part.
2.Sinus venosus.
3.Right half of Atrio ventricular canal.

45.  SINUS VENOSUS
 Left horn of sinus venosus –part of coronary
sinus.
 Right common cardinal vein becomes part of
superior vena cava.
 Right vitelline vein forms terminal part of
inferior vena cava.
 Right venous valve (right margin of sinu atrial
orifice) forms crista terminalis, valve of IVC,
& valve of coronary sinus.

47.  Left atrium is derived from :
1.Primitive atrial chamber-left half
2.Atrioventricular canal-left half
3.Pulmonary veins -absorbed proximal parts
 Single pulmonary vein opens into left half of
atrium –when septum primum just beginning to
form.
 Pulmonary vein bifurcates-right & left branches-
bifurcates-drain corresp. lung bud.
 Parts of pulmonary vein nearest to left atrium –
absorbed -4 pulmonary veins

49.  Fate of Bulbus Cordis
 Bulbus Cordis –divisible into conus (proximal
part) & truncus arteriosus (distal part).
 Spiral septum –union of right superior & left
inferior truncus swelling or cushions.
 Spiral septum appears within truncus
arteriosus & subdivides into ascending aorta
& pulmonary trunk.

50.  Conus (bulbus cordis proper) merges with
cavity of primitive ventricle .
 Right & left ventricle formed –partition of this
chamber.
 Bulboventricular cavity consists of :
Dilated lower part –communicates with atria.
Conical upper part-communicates with
truncus arteriosus.

54.  Septation of ventricles begins at day 25.
 Interventricular septum grows upwards from
floor of bulboventricular cavity-divides lower
dilated part into right & left halves.
 Interventricular septum fuses with fused
atrioventricular cushions.
 Right & left bulbar ridges arise from conical part
of bulboventricular cavity & fuse to form bulbar
septum.

55.  Bulbar septum grows towards interventricular
septum , doesnot reach it –gap left b/w two.
 Gap b/w upper edge of interventricular
septum & lower edge of bulbar septum –filled
by proliferation of tissue from atrioventricular
cushions.

56.  Inter ventricular septal defects
 1.VSD
 2.Tetralogy of Fallot
 3.Persistant truncus arteriosus
 4.Transposition of Great arteries

61.  Mitral & tricuspid valves formed –proliferation
of connective tissue under endocardium of
right & left atrioventricular canals.
 Pulmonary & aortic valves –endocardial
cushions formed at junction of truncus -
arteriosus & conus.

63.  3rd week of life ( 15-21 days)
 1.Splanchnopleuric mesoderm-18 days.
 2.Cavitation of mesoderm-intraembryonic
coelom-pericardial, pleural, peritoneal
cavities-18 days.
 3.Endocardial heart tube-20 days.
 4.Cardiac looping-21days.

64.  4 th week of life ( 22-28 days )
 1.Dvp. of left ventricle & right ventricle.
 2.Circulation commences.
 3.Cardiovascular septation.
 4.Aortic arches begins.

65.  5 th week of life ( 29-35 days )
 1.LV,RV,ventricular septum continue to grow.
 2.Approximation of aorta to interventricular
foramen, mitral valve,LV.
 3.Separation of ascending aorta,main
pulmonary artery.
 4.Separation of mitral & tricuspid valve.
 5.Tricuspid valve opens into right ventricle.
 6.Ostium primum closed by endocardial
cushions.

66.  6th & 7th week of life ( 36-49 days )
 1.Closure of conal septum
 2.Closure of membraneous part of ventricular
septum 38-45 days

67.  Blood vessel development by 2 mechanisms.
 1.Vasculogenesis-vessels arise by coalesence
of angioblasts.
 2.Angiogenesis-vessels sprout from existing
vessels.
 Dorsal aorta & cardinal veins –vasculogenesis.
 VEGF-vascular endothelial growth factor.

73.  Pharyngeal arches develop during 4 th & 5th
weeks of development.
 First arteries to appear in embryo-right & left
primitive aortae.
 Continuous with 2 endocardial heart tubes.
 Each primitive aorta-ventral aorta (lying
ventral to foregut), arched portion & dorsal
aorta (lying dorsal to gut).

74.  Fusion of 2 endocardial heart tubes-2 ventral
aorta partially fuse to form aortic sac.
 Unfused parts remain as right & left horns of
sac.
 Successive arterial arches appear in 2-6
pharyngeal arches, each connected ventrally
to right or left horn of aortic sac & dorsally to
dorsal aorta.

75.  Greater part of 1st & 2nd arch arteries
disappear ( 29 day embryo )
 Small portion of 1st arch artery persists to
form maxillary artery.
 Second arch artery form hyoid & stapedial
artery.
 Fifth arch artery also disappears.
 Aortic sac now connected with arteries of 3,4
& 6th arches.


76.  3rd & 4th arteries open into ventral part & 6th
arch arteries into dorsal part of aortic sac.
 Spiral septum formed in truncus arteriosus
,extends into aortic sac –fuses with posterior
wall-blood from pulmonary trunk passes into
6th arch artery –blood from ascending aorta
passes into 3rd & 4th arch arteries.
 Dorsal aorta b/w 3rd & 4th arches disappear
on both sides.

77.  Each 6th arch artery gives off artery to
developing lung bud.
 Right side-portion of 6th arch artery b/w lung
bud & dorsal aorta disappears.
 Left side-remains patent & forms ductus
arteriosus.
 Each 3rd arch artery gives off a bud –grows
cranially & form external carotid artery.

78.  Dorsal aorta gives off series of lateral
intersegmental branches to body wall.
 7th cervical intersegmental artery forms left
subclavian artery.

79. Arch Arterial derivative
1 arch Maxillary artery
2 arch Hyoid & stapedial artery
3 arch Common carotid & 1st
part of internal carotid
artery.
Left side of 4th arch Arch of aorta ( from left
common carotid to left
subclavian arteries ).
Right side of 4th arch Right subclavian artery
(proximal portion)
Left side of 6th arch Left pulmonary artery &
ductus arteriosus
Right side of 6th arch Right pulmonary artery

80.  Ascending aorta & pulmonary trunk –formed
from truncus arteriosus.
 Arch of aorta –from aortic sac, its left horn,
left 4th arch artery.
 Descending aorta-from left dorsal aorta,
partly from fused medial vessel.
 Brachiocephalic artery from right horn of
aortic sac.
 Common carotid artery from part of 3rd arch
artery.

81.  Pulmonary artery from 6th arch artery.
 Arteries to the gut-from ventral splanchnic
branches of dorsal aorta.
 Renal,supra renal & gonadal arteries –from
lateral splanchnic branches of dorsal aorta.
 Left subclavian artery –part of 7th cervical
intersegmental artery. Right side partly from
7th cervical intersegmental artery & right 4th
arch artery.

82.  Portal vein from right & left vitelline veins &
anastomosis b/w them.
 Superior vena cava from part of right anterior
cardinal vein & right common cardinal vein.
 Inferior vena cava from right posterior
cardinal vein, right subcardinal vein, right
supra cardinal vein, right hepato cardiac
channel.

83.  Heart develops from splanchnopleuric
mesoderm-cardiogenic area-3rd week.
 1.Establishment of cardiogenic field
2.Formation & position of heart tube
3.Cardiac looping
4.Cardiac septation
5.Aortic arch dvp.
 Heart begins to beat by day 22.

84.  Cardiogenesis begins on 18th day of life &
normally completed by 45th day of life with
formation of membraneous part of
interventricular septum.

85.  1.Kliegman, Stanton, Geme ST, Schor, Behrman. Nelson
Textbook of Pediatrics 19th edition 2012 :1527-1529.
 2.Sadler WT. Langmans Medical Embryology 10th edition
2012 :159-189.
 3.John FK, James EL, Donald CF Nadas Pediatric
Cardiology 2nd edition :14-25
 4.Myung K Park .Pediatric cardiology for Practitioners 2012
5th edition 120-180
 5.Inderbir singh, Pal PK. Human Embryology 8th edition
2012 :191-231