1. DEVELOPMENT OF HEART
Prof. Mujahid Khan

2. Objectives Describe heart tubes
List dilation and constrictions of heart tube
Describe endocardial cushion
Describe atrial septum
Describe ventricular septum
Describe oval fossa
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7/19/2019

3. Development of Heart
Primordium of heart is first evident at 18 days in the cardiogenic area
Mesenchymal cells aggregate side by side to form 2 cardiac primordia, Angioblastic cords
These cords canalize to form two thin walled endocardial heart tubes

5. Development of Heart
The endocardial heart tubes approach each other and fuse to form a single heart tube after lateral folding
Fusion of tubes begins at the cranial end of the developing heart and extends caudally

6. Primordial Myocardium
As the heart tubes fuse, an external layer of heart the primordial myocardium is formed from mesoderm
At this stage the developing heart is composed of a thin endothelial tube, separated from thick muscular tube by cardiac jelly

7. Endocardium
The endothelial tube becomes the internal endothelial lining of the heart, called endocardium
The primordial myocardium becomes the muscular wall of the heart or myocardium
The visceral pericardium or epicardium is derived from mesothelial cells and spread over the myocardium

8. After Folding As folding of head region occurs
The heart and pericardial cavity come to lie ventral (anterior) to the foregut and caudal (inferior) to the oropharyngeal membrane

10. Fate of Heart Tubes
The tubular heart elongates and develops alternate dilations and constrictions:
Truncus Arteriosus
Bulbus Cordis
Ventricle
Atrium
Sinus venosus
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7/19/2019

11. Fate of Heart Tubes
As the developing heart elongates and bends, it gradually invaginates into the pericardial cavity
Heart is now attached only at its cranial and caudal ends

12. Partitioning of Heart
Partitioning of the atrioventricular canal, primordial atrium, and primordial ventricle begins around 4th week
Completed by the end of the 5th week

14. Partitioning of Atrioventricular Canal
Toward the end of the 4th week
Endocardial cushions form on the dorsal (posterior) and ventral (anterior) walls of the AV canal
The AV endocardial cushions approach each other and fuse
Dividing the AV canal into right & left canals
These canals partially separate the primordial atrium from the ventricle
Endocardial cushion works as AV valves

16. Endocardial Cushion
It develops from a specialized extracellular matrix (ECM) or cardiac jelly
The transformed endocardial cushions contribute to the formation of the valves and membranous septa of the heart
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7/19/2019

18. Partitioning of Primordial Atrium
Beginning at the end of the 4th week
Is divided into right & left atria by the formation and subsequent modification and fusion of two septa:
Septum primum
Septum secondum

19. Septum Primum It’s a thin crescent shaped membrane
Grows from the roof of the primordial atrium towards the fusing endocardial cushions
Dividing the common atrium into left & right halves

23. Foramen Primum
A large opening forms in the growing septum primum between its crescentic free edge and the endocardial cushion
It serves as the shunt, enabling oxygenated blood to pass from right to the left atrium
Becomes progressively smaller and disappears as the septum primum fuses with the fused endocardial cushions to form a primordial AV septum

25. Foramen Secondum
Perforation appears in the central part of the septum primum before the foramen primum disappears
Perforation coalesce to form another opening, the foramen secondum
Concurrently, the free edge of the septum primum fuses with the left side of the fused endocardial cushions
Foramen secondum ensures a continuous flow of oxygenated blood from right to the left atrium

27. Septum Secondum A crescentic muscular membrane
Grows from ventrocranial wall of atrium
Immediately to the right of the septum primum
It is thick and grows during 5th & 6th weeks
Gradually overlaps the foramen secondum in the septum primum

29. Septum Secondum Its forms an incomplete partition between the atria
Consequently an oval foramen forms
Cranial part of the septum primum attached to the roof of it disappears gradually
Remaining part of septum primum (attached to endocardial cushion) forms a flap like valve of oval foramen

31. Oval Foramen
Before birth it allows most of the oxygenated blood entering the right atrium from IVC to pass into the left atrium
Prevents the blood flow in opposite direction
After birth it normally closes and the valve of the oval foramen fuses with septum primum
The interatrial septum becomes a complete partition between the atria

33. Oval Fossa
An oval depression in the lower part of the interatrial septum of the right atrium known as oval fossa
It’s a vestige of the oval foramen
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34. Partitioning of Primordial Ventricle
Division of primordial ventricle is first indicated by a median muscular ridge, the primordial interventricular septum
Is a thick crescentic fold has a concave free edge
Initially most of its height results from dilation of the ventricles on each side of the IV septum

36. Partitioning of Primordial Ventricle
Medial walls of the enlarging ventricles approach each other and fuse to form the primordium of the muscular part of the IV septum
Active proliferation of myoblasts in the septum increase its size
Until the 7th week there is a crescent shaped interventricular foramen between the free edge of IV septum and the fused endocardial cushion

38. Interventricular Foramen
The IV foramen permits communication between the right and the left ventricles
It usually closes by the end of the 7th week

40. Interventricular Septum
The membranous part of the IV septum is derived from an extension of tissue from the right side of the endocardial cushion to the muscular part of the IV septum

41. Interventricular Septum
After closure of the IV foramen and formation of the membranous part of the IV septum, the pulmonary trunk is in communication with the right ventricle and the aorta with the left ventricle

42. THE END
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7/19/2019