1. DEVELOPMENT OF CARDIOVASCULAR SYSTEM
Dr Samina Anjum

2. Learning Objectives
Septum formation in truncus arteriosus & conus cordis
Septum formation in ventricles
Valve formation
Formation of conducting septum
Clinical correlates

3. SEPTUM FORMATION IN THE ATRIOVENTRICULAR CANAL
At the end of the 4th week, two mesenchymal cushions, the atrioventricular endocardial cushions, appear at the superior and inferior borders of the atrioventricular canal.

4. In addition two other cushions, the lateral atrioventricular cushions, appear on the right and left borders of the canal.
By the end of 5th week, the superior and inferior cushions project further in the lumen and fuse, resulting in complete division of the canal into right and left atrioventricular orifices.

5. Scanning electron micrograph of heart from mouse embryo, showing growth and fusion of the superior and inferior endocardial cushions in the atrioventricular canal

6. ATRIOVENTRICULAR VALVES
After the atrioventricular endocardial cushions fuse, each atrioventricular orifice is surrounded by localized proliferations of mesenchymal tissue.

7. ATRIOVENTRICULAR VALVES
When tissue located on the ventral surface of these proliferations becomes hollowed out and thinned by the blood stream, valves are formed that remain attached to the ventricular wall by muscular cords.
Finally, muscular tissue in the cords degenerates and is replaced by dense connective tissue.

8. The valves then consist of connective tissue covered by endocardium and are connected to thickened trabeculae in the wall of ventricle, the papillary muscles, by means of chordae tendinae.
Two valve leaflets are formed in the left atrioventricular canal, the bicuspid or mitral valve, and three on the right side, the tricuspid valve.

9. SEPTUM FORMATION IN THE TRUNCUS ARTERIOSUS
During the 5th week, pairs of opposing ridges appear in the truncus.
These ridges, the truncus cushions/ conotruncal ridges, are located on the right superior wall (right superior truncus cushion) and on the left inferior wall (left inferior truncus cushion).

10. Cont…
The right superior truncus cushion grows distally and to the left, while the left inferior truncus swelling grows distally and to the right

11. Thus, the cushions twist around each other while growing towards the aortic sac.
After complete fusion, the ridges form a septum known as the aorticopulmonary septum, dividing the truncus into an aortic and a pulmonary channel.

12. SEPTUM FORMATION IN THE CONUS CORDIS
Similar cushions develop along the right dorsal and left ventral walls of conus cordis.
The conus cushions grow towards each other and in a distal direction to unite with the truncus septum.

13. The two conus cushions have fused, the septum divides the conus into an anterolateral portion conus arteriosus/infundibulum (the outflow tract of the right ventricle) and a posteromedial portion aortic vestibule (the outflow tract of the left ventricle).

14. SEPTUM FORMATION IN THE VENTRICLES
By the end of 4th week, the two primitive ventricles begin to expand due to continuous growth of the myocardium on the outside and continuous diverticulation and trabecula formation on the inside.

15. A crescent shape muscular partition begins to project upwards due to active growth from the floor of primitive ventricle.

16. The space bounded by the crescent edge of the muscular part of septum and the fused endocardial cushions is called interventricular foramen.

17. The growth of tissue from the inferior endocadial cushions along the top of the crescent upper edge of muscular interventricular septum closes the interventricular foramen. This completes the formation of the membranous part of the interventricular septum.

18. With the formation of right & left ventricles , the proximal portion of bulbus cordis become incorporated in right ventricle .

19. SEMILUNAR VALVES
When partitioning of the truncus has almost been complete, primordia of the semilunar valves become visible as small tubercles on the main truncus swelling.
One of each pair of tubercles is found on the orifices of pulmonary and aortic channels.
L.S through semilunar valves

20. Cont…
A third tubercle appears in both the channels opposite the fused truncus swellings.
Gradually, the tubercles are hollowed out at their upper surface, thus forming the semilunar valves, having a covering of endothelium over loose connective tissue.
Neural crest cells contribute in the formation of these valves.
L.S through semilunar valves

21. CONGENITAL ANOMALIES
Ventricular septal defects (VSDs): 12/10000 births
It involves the membranous or muscular portion (80%) of the septum.
It is the most common congenital cardiac malformations.

22. TETRALOGY OF FALLOT 9.6/10,000 births
Tetralogy of Fallot causes low oxygen levels in the blood. This leads to cyanosis.
It is the most frequently occurring abnormality of the conotruncal region.
The defect is due to the unequal division of the conus, resulting from anterior displacement of the conotruncal septum.

23. It includes four defects:
Pulmonary infundibular stenosis
Defect of interventricular septum
An overriding aorta arising directly above the septal defect or over the right ventricle
Hypertrophy of right ventricular wall due to high pressure on the right side.

24. PERSISTENT TRUNCUS ARTERIOSUS:
It results when the conotruncal ridges fail to fuse and to descend toward the ventricles.
The pulmonary artery arises some distance above the origin of the undivided truncus.

25. Cont…
Since the ridges also participate in the formation of the interventricular septum, the persistent truncus is always accompanied by a defective interventricular septum.
The undivided truncus thus overrides both ventricles and receives blood from both sides.

26. TRANSPOSITION OF THE GREAT VESSELS
PULMONARY VALVE ATRESIA
TRANSPOSITION OF THE GREAT VESSELS
It occurs when the conotruncal septum fails to follow its normal spiral course and descends straight downwards. As a result, the aorta originates from the right ventricle and the pulmonary artery originates from the left ventricle.
Ductus arteriosus is always patent
Pulmonary artery trunk is narrow or even atretic.
Oval foramen is patent
Ductus arteriosus is always patent

28. FORMATION OF CONDUCTING SYSTEM OF HEART
Initially, the pacemaker for the heart lies in the caudal part of the left cardiac tube.
Later, the sinus venosus assumes this function, and as the sinus is incorporated into the right atrium, pacemaker tissue lies near the opening of the superior vena cava. Thus the sinuatrial node is formed.

29. Cont…
The atrioventricular node and bundle (bundle of His) are derived from two sources:
Cells in the left wall of sinus venosus
Cells from the atrioventricular canal
Once the sinus venosus is incorporated into the right atrium, these cells are located in their final position at the base of the interatrial septum.

30. ECTOPIA CORDIS Rare anomaly Heart lies on the surface of chest
Due to failure of ventral body wall to close.

31. DEXTROCARDIA

32. THANK YOU