education

1. Embryology and Anatomy of the
heart

2. Introduction
• The first organ to develop
• Largely from mesoderm
• Begins middle of 3rd week till end of 8th week
• Chamber partition from mid 4th week to 8th week
• Events overlap

3. Day 18 -21 (week 3)

4. Day 22-23 (week 4)

5. Day 23 – 28 (week 4)

6. Late week 4 – week 5 (endocardial
cushion)

7. From end of week 4 (Day 28):Atrial
partition

8. Early week 5: Atrial partition ctd

9. Week 5 -6: Atrial partition ctd

10. Week 5- 6: Atrial partition

11. Week 4- 5: Pulmonary veins/Left
atrium
• 4 pulmonary veins develop as outgrowth of
the dorsal atrial wall just left of the septum
primum
• As the atrium enlarges, the pulmonary veins
become incorporated into the wall of the left
atrium.

12. Day 23-28 (Sinus venosus)
• Right and left sinus horns develop (lateral
protrusions from sinus venosus)
• Both horns initially equal
• Right horn progressively enlarges
• By day 28, it is larger and sinoatrial orifice
moves to the right.
• SVC and IVC open into it
• Right horn eventually incorporated into right
atrium
• Left horn becomes coronary sinus

13. Week 5: Bulbous cordis & Truncus
arteriosus
• Mesenchymal cells proliferate in the walls
forming bulbar and truncal ridges which are
continuous with each other.
• The bulbar and truncal ridges undergo 180
degrees spiralling
• Results in spiral aorticopulmonary septum on
fusion of the ridges

14. Week 5: Bulbous cordis & Truncus
arteriosus
• It divides into the ascending aorta and the
pulmonary trunk
• Because of the spiralling of the septum, the
pulmonary trunk twists round the ascending
aorta
• The bulbous cordis becomes incorporated into
the walls of the ventricle

15. Week 5: Bulbous cordis & Truncus
arteriosus

16. Mid 4th week –end 7th week: Ventricles

17. Mid 4th week –end 7th week: Ventricles

18. Week 7: Membranous interventricular
septum (IVS)
• Formed by extension of tissue from right side of
the endocardial cushion to the muscular part of
IVS
• Merges with tissues from the bulbar ridges of the
aorticopulmonary septum
• After closure, the pulmonary trunk/aorta are
aligned and in communication with their
respective ventricles
• Cavitation of the walls lead to trabeculae,
pappilary muscles, and chordae tendinae

19. End of week 7

20. Valves
• Semilunar valves develop from 3 swellings of
subendocardial tissue around the orifices of the
aorta and pulmonary trunk when the truncus
arteriosus partition is near completion
• These swellings become hollowed out and
reshaped into 3 thin wall cusps.
• The atrioventricular valves develop similarly from
subendocardial tissues around the AV cannal.

21. The primitive aortic arches
• Of the 6 pairs of primitive aortic arches, 1st, 2nd and and
5th regress completely.
• Proximal portion of the 6th arches become the right and
left pulmonary arteries
• The distal left 6th arch becomes the ductus arteriosus
• The 3rd arch forms connection between internal and
external carotid arteries
• The 4th becomes the segment between left carotid and
subclavian arteries