تطور تكوين القلب

1. Development of the Heart
DR.FATHIA ALAZZI

2. Development of muscular part of
interventricular septum :
Primordial muscular
interventricular( IV )septum
arises in the floor of ventricle
, as thick crescentic fold with
concave free edge.
This septum subdivides the
original ventricular cavity
incompletely into right & left
ventricles that communicate
together through IV foramen.
This foramen closes by the
end of 7th week as the 2 bulbar
ridges fuse with the endocadial
cushion.
A-sagittal section 5th week.
Coronal section.6th week.

3. Closure of IV foramen & formation
of membranous part of IV septum
result from fusion of the following :
1-right bulbar ridge.
2-left bulbuar rige.
3-fused endocardial cushions.
A,sagittal s.at 5th w.
B, coronal s.at 6th w.after
incorporation of the proximal part of
bulbus cordis into the ventricles.
C,5th w.,showing the bulbar ridges
& fused endocardial cushions.
D,6th w., proliferation of endocardial
cushions to diminish I V foramen.
E,7th w.,fusion of bulbar ridges +
extensions of endocardial cushions
upward with aortico-pulmonary septum
and down with muscular I V septum to
close I V foramen , so memb. IV
septum is formed

4. A sagittal s.at 5th w., showing the
bulbus cordis in the primitive heart.
B coronal s.at 6th w. after
incorporation of the proximal part of
bulbus cordis into the ventricles to
forms :
In right ventricle …Conus arteriosus
(infundibulum), which gives origin of
pulmonary trunk.
In left ventricle…. Aortic vestibule part
of ventricular cavity just inferior to aortic
valve.
Incorporation of the
proximal part of bulus
cordis into the ventricles

5. Cavitation of Ventricular Walls
Leads to formation of
spongy muscular bundles
(trabeculae carneae).
These bundles become
the papillary muscles &
tendinous cords
(attached to the cusps of
tricuspid & mitral valves).
A-5 weeks.
B-6weeks.
C-7weeks.
D-20 weeks.

6. Partitioning of distal part of the Bulbus
Cordis & Truncus Arteriosus :
A, 5th w. ventral v.of heart.
B,5th w. transverse sections of truncus
arteriosus & bulbus cordis,illustrating
truncal & bulbar ridges.
C,5th w. truncal & bulbar ridges , after
removal of ventral wall of heart &
truncus arteriosus.
D,heart after partitioning of truncus
arteriosus into aorta & pulmonary trunk.
E, transverse sections through newly
formed aorta & pulm.trunk showing
aortico-pulmonary septum.
F,6th w.removal of ventral wall to show
aotico-pulmonary septum.

7. Partitioning of distal part of the Bulbus
Cordis & Truncus Arteriosus :
G,diagram illustrating the spiral
form of aortico-pulmonary
septum.
H,drawing showing aorta &
pulmonary trunk twisting around
each other as they leave the
heart.

8. Partitioning of distal part of the Bulbus
Cordis & Truncus Arteriosus :
 During 5th w. firstly , a right &
left bulbar ridges are developed
in the lower part.
Another ant.& post. Bulbar
ridges in the middle part.
Right & left truncal ridges are
developed in the upper part.
Bulbar & truncal ridges are
developed from proliferation of
mesenchymal cells of their wall.
They are also derived from neural
crest mesenchyme by passing through
the primitive pharynx

9. Partitioning of distal part of the Bulbus
Cordis & Truncus Arteriosus :
 as development proceeds, the
ridges fuse together following a
spiral course, forming aortico-
pulmonary septum which has a
spiral shape at the 6th week ,
(as in G).
This septum divides bulbus
cordid & truncus arteriosus into
aorta & pulmonary trunk.
Because of spiraling of aortico-
pulmonary septum, pulm.trunk twists
around the aorta. Firstly pulm.trunk lies
ant.& to right of the aorta near the
ventricles, then upward,it lies post. & to
left of aorta.

10. Development of Atrioventricular Valves
A,5thw.,showing right &
left AV canals and
begining of valve
swellings due to
proliferations of tissue
(subendocardial tissue)
around AV canals.
B,6th w.
C,7th w. complete
development of tricuspid
& mitral valves….. Note
also development of
compelete interventricular
septum(muscular+memb.part)

11. 3 Semilunar valves
begin to develop from 3
swellings of
subendocardial tissue
around aortic &
pulmonary orifices.
These swellings are
hollowed out to form the
thin walled semilunar
cusps.
Results after
development of bulbar &
truncal ridges and formation of
aorticopulmonary septum.
Development of aortic & pulmonary valves :

12. Development of aortic & pulmonary valves
A, long. Section showing
bulbar & truncal ridges.
B, transverse section of
bulbus cordis.
C,fusion of bulbar ridges.
D,formation of walls & valves
of aorta & pulmonary trunk.
E, rotation of the vessels &
the valves.
F, long.sections showing
hollowing & thinning of valve
swelling to form the cusps.

13. Development of conducting system :
Sinuatrial (SA) node
begins to develop during 5th
w.as it is present in right wall
of sinus venosus.
SA-node is incorporated
into wall of right atrium with
sinus venosus. SA-node is
located high in the right
atrium ,near entrance of SVC.
Right sinuatrial valve
(cranial part)…. Forms crista
terminalis,but the caudal part
…forms the valves of IVC &
coronary sinus.

14. Development of conducting system :
Left sinuatrial valve is
incorporated into the
interatrial septum forming AV-
node & bundle ,which are
located superior to
endocardial cushions.
Right & left bundle
branches arising from AV-
bundle , pass from atrium into
the ventricular myocardium.
A band of C.T. grows in
from the epicardium and
separates the muscle of atria
from that of ventricles to form
the cardiac skeleton
(fibrous skeleton of heart).

15. Anomlies of heart
1- anomlies in position
Dextrocardia
2- anomlies in atrial septum(Atrial Septal
defects (ASD)
• patent foramen ovale).most common
• ostium secundum defect.
• common atrium..
Rare cardiac defect ,in which the interatrial
septum is absent due to failure of septum
primum & septum secundum to develop.

17. 3-Anomlies of IV septum
• Defect in membranous septum
• Completely absent IV septum
4-anomalies in bulbus cordis
• Tetralogy of Fallot
• Persistant bulbus cordis
• Transposition of aorta & pulmonary
trunk
5-anomlies in valves
• Aortic stenosis
• Pulmonary stenosis

18. Ventricular Septal Defects (VSDs):
Membranous VSD …. Is the most common type.
Results from incomplete
closure of IV foramen due to
failure of development of memb.
part of IV septum.
Large VSDs with excessive
pulmonary blood flow &
pulm.hypertension result in
dyspnea (difficult breathing) +
heart failure.

19. Or absence of the IV septum--Single
ventricle + Transposition of aorta &
pulmonary trunk.
Complication: heart failure and
death.
This diagram showing transposition
of great arteries (TGA) which leads to
cyanosis. VSD+ASD allow mixing
arterial & venous blood.
Transposition results from that the
aortico-pulmonary septum descends
straight (instead of spiral).

20. Tetralogy of Fallot : It contains 4 cardiac
defects :
1- Pulmonary stenosis
(obstruction of right
ventricular outflow).
2- Ventricular Septal Defect
(VSD).
3- Dextroposition of aorta
(overriding aorta).
4- Right ventricular
hypertrophy.
 cyanosis is one of the
obvious signs of tetralogy .

22. Development of blood vessls
Mesenchymal cells blood island
blood vessel
Development of arteries from
• Two dorsal aortae &their branches
• Two ventral aortae
• Six pairs of pharyngeal arch arteries

23. The Aortic Arches Derivatives :
During the 4th week, as the
pharyngeal arches develop, they
are supplied by the aortic
arches.
Aortic arches arise from the
aortic sac and terminate in the
dorsal aorta.
There are 6 pairs of aortic
arches, but they are never
present at the same time.
During 8th w.,the primitive
aortic arch pattern is
transformed into final fetal
arteries.

24. Aortic Arch Arteries :

25. Left side embryonic cardiovascular
system (26 days) 4 –week embryo :
The paired dorsal aortae fuse to form a
single dorsal aorta, just caudal to the
pharyngeal arches.
Branches of the dorsal aorta :
1- Cervical dorsal intersegmental arteies join
to form vertebral artery on each side
(7th cervical intersegmental artery forms the
subclavian artery).
2- Thoracic dorsal intersegmental arteries
persist as intercostal arteries.
3- in the lumbar region, they persist forming
lumbar arteries, but 5th lumbar enlarge and
forms common iliac artery.
4- in the sacral region, they form lateral
sacral arteries , but the caudal end of dorsal
aorta becomes the median sacral artery.

26. The aortic Arches :
A, left sided-embryo (26-
days) showing the
pharyngeal arches.
B, schematic drawing
showing left aortic arches
arising from the aortic sac.
C, an embryo (37days),
showing the single dorsal
aorta and degeneration of
most of the first two pairs
of aortic arches.

27. Development of the final fetal arterial pattern :
A, aortic arches at 6 weeks, note
largely disappearance of the first two
pairs of aortic arches.
B,aortic arches at 7 weeks, showing
normal degeneration of aortic arches
and dorsal aortae.
C, final arterial arrangement at 8
weeks, note open ductus arteriosus.
D, 6-month-old infant, note the final
arrangement of the vessels - and that
the ascending aorta & pulmonary
arteries are smaller in C than in D.
Note also, obliterated & fibrosed ductus
arteriosus forming … ligamentum
arteriosum within few days after birth.

28. Derivatives of 1st & 2nd pairs of aortic arches
:
The 1st aortic arches
largely disappear. small
parts persist to form the
maxillary artereis.
The 2nd aortic arches
disappear leaving small
parts forming the stapedial
artereis (run through the
ring of the stapes, a small
bone in middle ear).

29. Aortic Arches Arteries

30. Derivatives of 3rd & 4th pairs of aortic arches :
The 3rd arch artery persists forming
the common carotid artery and proximal
part of internal carotid artery (on both
sides), it joins with the dorsal aorta to
form the distal part of int.c.artery. The
ext.c.artery develops as a new branch
from 3rd arch.
The 4th arch forms the main part of
the arch of aorta… on left side,
and forms the proximal part of right
subclavian artery … on the right side.
 The distal part of Rt.subclavian artery
develops from the right dorsal aorta &
right 7th intersegmental artery.
The left subclavian artery …. is not
derived from aortic arch but from the
left 7th intersegmental artery.
Proximal part of the arch of
aorta develops from the aortic
sac , and the distal part
from left dorsal aorta.

31. Aortic arches arteries

32. Derivatives of 5th & 6th pairs of aortic arches :
The portion of dorsal aorta
connecting the 3rd & 4th arches
disappears on both sides.
The 5th arch artery disappears in
50% and in the other 50% of the
embryos, these arteries do not
develop.
The 6th arch artery :
a- proximal part on both sides …
forms the pulmonary artery.
b- distal part of left artery : forms
ductus arteriosus which connects left
pulmonary artery with arch of aorta.
C- distal part of right artery :
disappears.
The dorsal aorta on the
right side caudal to 4th arch
disappears down to the single
dorsal aorta, while persists on
left side to form descending
aorta.

33. Aortic Arches Arteries

34. Development of aorta
1- its proximal part
develops from left part
of distal part of aortic sac
(right part of aortic sac
forms brachio -cephalic
artery).
Proximal part of aortic
sac forms the pulmonary
trunk.
2- its main middle part
develops from left 4th
aortic arch.
3- its distal part
develops from the left
dorsal aorta between 4th &
6th aortic arches.

35. Final development of the arteries from the aortic
arches arteries :

36. The relation of recurrent laryngeal
nerves to the aortic arches :
A, 6-weeks, showing R.L.Ns.
hooked around the distal part of
6th pair of aortic arches.
B, 8-weeks, showing the
Rt.R.L.N. hooked around the
Rt. Subclavian artery, and the
left R.L.N. hooked around the
ductus arteriosus & arch of
aorta.
Child, showing the left R.L.N.
hooked around ligamentum
arteriosum & arch of aorta.

37. Development of Recurrent Laryngeal Nerves :
Firstly, these nerves supply the 6th
pharyngeal arch so, they hook around
the 6th pair of aortic arches.
On the right , the distal part of right
6th aortic arch degenerates ,so right
R.L.N. hooks around the right
subclavian artery.
On the left , the left R.L.N. hooks
around the ductus arteriosus formed
by the distal part of 6th aortic arch.
 when DA is transformed after birth
into ligamentum arteriosum ,left
R.L.N. hooks around lig.arteriosum &
arch of aorta.

38. Coarctation of the aorta :
A, postductal coarctation of aorta.
B, development of collateral
circulation.
C and D, preductal coarctation.
E, 7-week embryo, showing normal
area of involution in the distal segment of
right dorsal aorta as the right
subclavian artery develops.
F, abnormal area of involution in the
distal segment of the left dorsal aorta.
G, later stage, showing the abnormally
involuted segment appearing as a
coarctation of aorta which moves with
the left subclavian artery to the region of
ductus arteriosus….. E to G illustrate
one hypothesis about the embryological
basis of coarctation of aorta.

39. Coarctation of Aorta :
In postductal coarctation
, the constriction is distal
(below) to ductus arteriosus.
This permits development of
a collateral circulation during
the fetal period to assist
passage of blood to lower
part of the body.
In preductal coarctation ,
the constriction is proximal
or above the ductus
arteriosus which remains
open and maintain the
circulation (below the
narrowing) to the lower part
of the body.