The heart develops from cardiogenic mesoderm and forms endothelial heart tubes that fuse to create a single heart tube located within the pericardial cavity. The heart tube undergoes looping to form the basic chambers and portions. Septae then develop to divide the heart into four chambers - the interatrial septum divides the atria while the interventricular and aorticopulmonary septa divide the ventricles. Various congenital malformations can occur if septation is incomplete or unequal. The great arteries also septate during development.

1. Dr. Sandip Gupta
PGT – Pediatrics
BSMCH
Development of Heart
&
Congenital Malformations

2. Development of the heart
Develops from splachnopleuric mesoderm lying immediately cranial to the
pro-chordal plate. This medoderm constitutes cardiogenic area
Cells of the area migrate between mesoderm and endoderm and arrange as
to longitudinal cellular strands called cardiogenic cords
cords become canalized to form two thin-walled endothelial tubes - called
endocardial heart tubes

3. Formation of Single heart tube & pericardial cavity
As the lateral folds develop, the
endocardial heart tubes gradually
approach each other and fuse from
the cephalocaudal direction to form
a single unpaired heart tube
Fusion of endocardial heart tubes
into one single is followed by a
fusion of paired pericardial cavities
so that finally
single (common) pericardial cavity
arises

4. • If the fusion is completed, the
heart tube lies within the pericardial
cavity and is attached to its dorsal
side by a fold of mesodermal tissue -
the dorsal mesocardium
• The dorsal mesocardium is transitory
structure that soon degenerates
• After disappearing of the mesocardium,
the heart tube is freely housed in the
pericardial cavity, being firmly fixed only
at two sites:
at arterial (cranial) and
venous (caudal) ends
the single heart tube stage is
achieved during the 23 -24 day
when the heart begins regularly to
beat

5. Formation of the heart wall
as the heart tubes fuse, the mesenchyme around
them proliferates and forms a thick layer of cells -
myoepicardial mantle
from the endothelium of the heart tube the
myoepicardial mantle is separated by cardiac jelly - a
gelatinous connective tissue
cells of the myoepicardial mantle differentiate into:
- mesothelial cells - outermost layer called epicardium
(visceral pericardium)
- myoblasts - cardiomyocytes of myocardium
cells of cardiac jelly give rise to subendocardial layer
of endocardium(PURKINJE FIBERS)
the mentioned processes result in three-layered
composition of the heart wall known from microscopic
anatomy:
the inner endocardium, the middle myocardium, and
the outer epicardium

7. • Development of the heart tube then continues by its uneven growth in the
width and Length,
• As a result it distinguishes in several portions in caudocranial axis there are
as follows :
sinus venosus - venous end, receiving blood from the umbilical,
vitelline and common cardial veins on each side
primitive atrium - separated from the sinus by a terminal sulcus,
primitive ventricle - separated from the atrium by the AV sulcus,both
portions are connected each other with an AV foramen.
bulbus cordis - is continuous with ventricle through the primary
interventricular foramen;
--this portion will give rise to part the definitive right ventricle
truncus arteriosus - arterial end of the tube, which divides into paired
ventral aortae

8. Formation of the Cardiac Loop
• The heart tube
continues to elongate
and bend on day 23.
The cephalic portion of
the tube bends
ventrally, caudally, and
to the right. And the
atrial (caudal) portion
shifts dorsocranially and
to the left.
• This bending, which may
be due to cell shape
changes, creates the
cardiac loop. Completed
by day 28.

9. Septation of the heart
The septation process = division of the heart into two halves
down midline
the process begins in the 5th week and ends in a week later
3 septae take part in division of the heart in the right and left
chamber
there are as follows:
interatrial septum
interventricular septum
aorticopulmonary septum

10. Ventral
endocardiac
cushion
Dorsal
endocardiac
cushion
Atrioventricular
tube
Left
atrioventricular
tube
Right
atrioventricular
tube
Compartmentation of heart
27 - 37th day

11. Compartmentation of primitive atrium
( 4th to 5th week)

13. Anomalies of atrial septum formation

14. Compartmentation of primitive ventricle
(4th -8th wk)

15. The medial walls of the expanding ventricles become apposed and gradually
merge, forming the muscular IVS.
The IV foramen, above the muscular portion of the IVS, shrinks on
completion of the conus septum. outgrowth of tissue from the inferior
endocardial cushion along the top of the muscular interventricular septum
closes the foramen This tissue fuses with the abutting parts of the conus
septum. Complete closure of the interventricular foramen forms the
membranous part of the IVS.

16. Anomaly of ventricular septum development

17. Septum Formation In The Atrioventricular Canal
• At the end of the fourth week, two mesenchymal cushions, the AV
endocardial cushions, appear at the superior and inferior borders of
the AV canal.
• In addition to the superior and inferior endocardial cushions, the two
lateral atrioventricular cushions appear on the right and left borders of
the canal

18. Compartmentation of truncus arteriosus
and bulbus cordis

19. Malformation of cono-truncal region
• No septum formation : failure of conutruncal ridges to fuse
-Truncus Arteriosus.
• when the conotruncal septum fails to follow its normal spiral
course and runs straight down - TGA
• Unequal compartmentation : - TOF, PS

20. PTA

21. TGA

22. TOF

24. PDA - Patent Ductus Arteriosus

25. • 1st aortic arch – disappears
• 2nd aortic arch – disappears
• 3rd aortic arch - has the same development on the right and left
side it gives rise to the common carotid artery & initial portion of
the internal carotid artery.
•4th aortic arch - has ultimate fate different on the right and left
side on the left - it forms a part of the arch of the aorta between
left common carotid and left subclavian artery on the right - it
forms the proximal segment of the right subclavian artery
•5th aortic arch - is transient and soon obliterates
•the 6th aortic arch - pulmonary arch

26. ABNORMALITIES OF AORTA
• Coarctation of Aorta: narrowing below subclavian
artery.
• Double Aortic Arch:Rt dorsal Aorta persists betwn
the origin of 7th intersegmental artery & its
junction with Lt dorsal Aorta
• Right aortic Arch: Lt 4th arch& Dorsal aorta are
obliterated & replaced by counterparts on Rtside
• Interrupted Aortic Arch: obliteration of the 4th
Aortic Arch on Lt side.

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