2. INTRODUCTION
• Cardiovascular system starts to develop by middle of 3rd week of
intrauterine life.
• Heart starts to beat by early 4th week (23 rd day).
• Entire process of heart development completes by 7th week.
• Crucial period for development of anomalies is 3 - 6 weeks.
3. PRIMARY HEART FIELDS
• Progenitor heart cells lie in
the epiblast, from they
migrate to splanchnic
mesoderm, which forms
primary heart fields.
• PHF
1. Atrium
2.Left ventricle
3. Parts of right ventricle.
.
4. SECONDARY HEART FIELDS
• Secondary heart fields(SHF)
develop in the splanchnic
mesoderm ventral to pharynx.
• SHF
1. Parts of Right ventricle
2. outflow tract ( conus cordis
and truncus arteriosus)
• SHF - Laterality of heart which
occurs on day 16
5. Molecular regulation- HEART FIELDS
• Induction of heart by NKX 2.5.
• BMP 2 & 4 Secreted by
endoderm and lateral plate
mesoderm.
• WNT INHIBITION by CRESCENT
and CEREBRUS -.
• RETINOIC ACID(RA) – contribute
to the venous portion of heart
tube.
6. LEFT SIDEDNESS
5 - HT - transcription factor
PITX2.
PITX2 - master gene for left
sidedness.
Laterality defects such as
dextrocardia, VSD, ASD, DORV,
OUTFLOW Defects occurs.
Tertogenicity of SSRI explains the
importance of 5 –HT Signaling
pathway.
7. Heart tube formation
• PHF are induced by the
endoderm to form cardiac
myoblasts and blood islands.
• Blood islands will forms blood
cells and vessels by
vasculogenesis.
• Blood islands unite and forms a
horseshoe shaped endothelial
tube , cardiogenic region.
• Pericardial cavity develops over
it
8. Formation and position of heart tube
• Cardiogenic area lie anterior to
oropharyngeal membrane.
• Growth of the brain and cephalic
folding of embryo pulls the
oropharyngeal membrane
cranialy ,while heart and
pericardial cavity moved first to
cervical region and then to
thorax.
• .
9. • As a embryo grows and bends
cephalocaudally, caudal regions
of the paired cardiac tube
merges except at the
caudalmost parts
• Central parts of the heart tube
expands to form the outflow
tract and ventricular regions
10. • Now the heart becomes a
continuous tube with an inner
endothelium and an outer
myocardial lining.
• Heart tube remains attached to
dorsal side of pericardium by the
dorsal messocardium.
• Middle section of dorsal
mesocardium disappears and
forms transverse pericardial sinus
which connects both sides of the
pericardial cavity.
• Myocardium thickens and secrete a
layer of ECM called cardiac jelly .
11. • Heart tube consists of three
layer
1.Endocardium – internal
endothelial lining of heart.
2. Myocardium – muscular wall
3. Epicardium – visceral
myocardium, formation of
coronary arteries
12. Cardiac looping
• Heart tube continues to elongate
as cells are added from SHF to its
cranial end.
• Lengthening process is essential
for normal formation of part of
right ventricle and outflow tract
region and looping process.
13. • Cardiac tube begins to bend on
day 23 and completes on day 28
• Cephalic portion of the tube
bends ventrally, caudally and to
the right.
• Caudal (atrial) portion shifts
dorsocranially and to the left.
14. Cardiac looping
• Conotruncal portion of heart tube
moves from the right side of
pericardium to the more medial
position,results from the formation
of two transverse dilations of
atrium.
• Trabeculae occurs in the primitive
ventricle becomes left ventricle.
• Bulboventricular sulcus – junction
between the ventricle and bulbus
cordis. Its called the primary
interventricular foramen.
15. Bulbus cordis
Proximal parts :
• Trabeculated parts of the right
ventricle
• Conus cordis :
Outflow tracts of both ventricle.
• Truncus arteriosus –
• Roots and proximal portion of aorta
and pulmonary artery.
16. Sinus venosus development
Each horns receives
• 1. viteline veins
• 2.. Umblical veins
• 3. common cardinal veins.
• During 4th and 5th week shifting
occurs predominantly to right -
obliteration of left vitelline veins
at 5th week and obliteration of
left common cardinal veins at
10th weeks
17. Cont..
• Only oblique vein of left atrium
and coronary sinus persists.
• Right sinus horns - smooth
walled part of right atrium.
• Sinus venosus also gives rise to
the visceral pericardium of the
heart.
• Some of sinus venosus cells
infiltrate into the heart and forms
the conducting system of the
heart.
18. • Its entrance sinuatrial orifice
flanked on each side by rt and lt
venous valves.
• Dorsocranially valves fuses and
forms a sputum spurium.
• Lt venous valve and sputum
spurium helps in the development
of atrial septum
• Rt venous valve develops into
• 1.valve of IVC
• 2. valve of coronary sinus
19. Abnormalities of cardiac looping
• Dextrocardia : the location of the heart in the right hemithorax with
the base to apex axis to the right
• Mesocardia : cardiac base to apex axis directed to the midline of the
thorax or with ventricular apices equally directed to both right and
left sides
20. Cardiac septa formation
1.Endocardial cushions-
septum formation by two
actively growing ridges
2. septum formation by single
actively growing cell mass,
such as septum primum and
septum secundum.
3.IVS - septum formation by
merging two expanding
portions of the walls of heart.
21. Formation of interatrial septum
• Septum primum –
• End of 4th week
• Sickle shaped crest grows from
the roof of common atrium
towards endocardial cushions.
• Opening between the lower rim
of septum primum and
endocardial cushions – ostium
primum.
22. Cont..
• Superior and inferior
endocardial cushions grows
along the edge of septum
primum and closes the ostium
primum.
• Before closure , cell death occurs
in the upper portion of septum
primum and forms the ostium
secundum
23. • New crescent shaped fold called
septum secundum appears .
• Left venous valve and septum
spurium fuse with the right side
of the septum secundum .
• It overlap the ostium secundum
• The opening left by ostium
secundum is called oval foramen
(foramen ovale)
• Remaining parts of septum
primum becomes the valve of
the oval foramen.
24. Formation of left atrium and pulmonary veins
Dorsal mesenchymal
protrusion(DMP) - the
proliferating mesenchyme of
the dorsal mesocardium.
This tissues grows with the
septum primum towards the
atriventricular canal.
25. • Pulmonary veins is positioned.
• Remaining parts of DMP
contributes to endocardial
cushion formation.
Clinical correlates:
TAPVR
26. AV CANAL SEPTUM FORMATION
• FOUR endocardial cushions
appears at the end of 4 weeks.
• AV CANAL access only to
primitive left ventricle and is
separated by bulbo ventricular
flange.
• At the end of fifth
week,posterior extremity of
flange terminates midway along
the base of dorsal endocardial
cushions.
27. • AV canal enlarges to right -
direct access to rt and lt
ventricle.
• Two lateral endocardial cushions
appear on the right and left
borders of canal.results into rt
and left av valves
• Each AV Orifices is surrounded
by local proliferations of
mesenchymal tissues
• Blood flows hollows out,
mesenchymal tissue becomes
fibrous and forms the AV
VALVES.
28. • AV valves remain attached to the ventricular wall by the muscular
cords.
• Muscular cords degenerates and is replaced by dense connective
tissues to become chordae tendinae.
• AV Valves are connected to the papillary muscles by means of
chordae tendinae.
29. Septum formation in the truncus arteriosus
and conus cordis
• Right superior truncus swelling
grow distally and to the left and
on
the left inferior truncus grow
distally and on the right.
• Swelling twisted around each
other and forms the
aorticopulmonary septum
divides the truncus into an aortic
and pulmonary channel.
30. Cont..
• Similar swellings appear on the
dorsal and ventral walls of conus
cordis ,grows towards each
other and distally to unite with
the truncus septum.
• Septum divides the conus into
an anterolateral portion
(outflow tract of RV) AND
POSTEROMEDIAL
portion(outflow tract of LV)
31. INTERVENTRICLUAR SEPTUM- MUSCULAR
PART
• By the end of 4TH week ,two
primitive ventricles begin to
expand.
• Medial walls of the expanding
ventricles become apposed and
gradually merge – muscular
ventricular septum.
32. • Interventricular foramen – space
between the free rim of muscular
ventricular septum and fused
endocardial cushions.
• Interventricular foramen closes by
completion of conus septum and
outgrowth of tissue from the
anterior endocardial cushions
along the top of muscular
interventricular septum.
33. BULBAR PARTS
• Right and left bulbar ridges arise
in bulboventricular cavity
• These ridges grows towards each
other to form bulbar septum
• Grows downwards towards
muscular part of IVS but does
not reach it
34. MEMBRANOUS PARTS
• Proliferation of tissue from
inferior A-V endocardial
cushions fills the gap between
muscular and bulbar parts of IVS
• TWO parts :
• INTERVENTRIULCAR
• ATRIOVENTRICULAR – separates LV
& RA
35. Semilunar valves
• Semilunar valves visible as small tubercles found on the main truncus
swellings.
• Third tubercle appear in both channels opposite the fused truncus
swellings.
• Tubercles hollow out at their upper surface forming semilunar valves.
• Neural crest cells contribute to the formation of semilunar valves.
36. Aortic Arch
• Each pharyngeal arch has own
cranial nerve and arteries.
• Aortic arches arise from the aortic
sac ,the most distal part of truncus
arteriosus.
• .
• By day 27,most parts of 1st and 2nd
arch disappears.
• First arch artery is represented by
maxillary artery.
• Second arch artery is represented
by stapedial artery.
37. • 3rd arch
• Common carotid artery
• Part of internal carotid artery
• External carotid atery arises as
sprout from 3rd arch
5th arch fails to form
38. FOURTH ARCH
4th arch on right
• Proximal segment of
subclavian artery
• Distal segment - 7th
intersegmental and Rt dorsal
aorta.
4th arch on left
Arch of aorta
39. • 6th arch on right
• Right pulmonary artery
• Distal segment regress
6th arch on left
• Left pulmonary artery
• Distal segment as ductus
arteriosus
• .
40. Venous system
Inferior vena cava
• Rt Vitelline veins –
hepatocardiac portion of ivc
• Rt subcardinal veins – renal
segment of ivc
• Rt sacrocardinal veins.
Superior venae cava
ANASTOMOSIS of rt common
cardinal veins and proximal
portion of right anterior cardinal
veins.
41. Conducting system of heart
• Pacemaker for the heart lies in the caudal part of the left cardiac
tube.
• AFTER cardiac looping ,sinus venosus assumes this function’
• Pacemaker lies near the opening of svc into the right atrium ,thus
sinoatrial node is formed.
42. • Av node and bundle of his are derived from two sources:
1.myocardial cells in the left wall of sinus venosus.
2.myocardial cells from AV Canal.
43. NEURAL CREST CELLS
• Cardiac neural crest cells - the
formation endocardial formation in
both conus and truncus arteriosus.
• Neural crest cells - the smooth
muscle and connective tissues of
the arch vessels.
• Heart defects caused by this
mechanism include TOF,PS,PTA
AND TGA.
