1. EMBRYOLOGY

2. Highlights…………………. Implantation Types and normal site of implantation
Clinical aspects – placenta prevea
Formation of endoderm
Formation of ectoderm
Secondary yolk sac
Extra embryonic mesoderm

3. First week of intra uterine life

4. SECOND WEEK OF INTRA UTERINE LIFE

7. Prochordal plate
Buccopharyngeal
membrane
Primitive streak
Cloacal membrane

8. DEVELOPMENT OF NOTOCHORDAL PROCESS

9. TRANSFORMATION OF NOTOCHORDAL PROCESS

12. Formation of mesoderm

13. SUBDIVISIONS OF INTRA EMBRYONIC MESODERM
Separates the ectoderm and endoderm except at :
Prochordal plate, cloacal membrane and in the midline where the notochord is present.
At the edge both intra and extra embryonic mesoderm
are continuous.
The three divisions of the intra embryonic mesoderm:
1. Paraxial mesoderm.
2. Lateral plate mesoderm and
3. The intermediate mesoderm.

14. X Y Prochordal plate Paraxial Mesoderm Primitive streak Intermediate

15. Endoderm
Notochord
Intermediate mesoderm

16. Paraxial mesoderm segments into cubical masses - the somitomeres which form the somites.
Small cavities appear in the lateral plate mesoderm,which join together to form the intra embryonic coelom.
The horse shoe shaped cavity joins in the midline cranial
to the prochordal plate.
Intra embryonic coelom divides the mesoderm into somatopleuric and splanchnopleuric mesoderm.
The coelom gives rise to pericardial, pleural and the
peritoneal cavities.

17. Neural plate Y X

18. Neural plate
Lateral plate mesoderm

19. Intra embryonic coelomX Y

20. X Y
Intra embryonic
coelom opening

21. Amniotic cavity A B C

22. Somatopleuric mesoderm
Ectoderm

23. The heart is developed from the splanchnopleuric
mesoderm cranial to the prochordal plate and this area
is the cardiogenic area
Cranial to the cardiogenic area the mesoderm
does not split.It forms the future septum transversum

24. Fate of the somites
The paraxial mesoderm forms segments- the somites
that lie on either side of the neural tube.
Somite period – days of development
Total number of somites – 44 pairs
The somites are divided into three parts:
1. Ventromedial - Sclerotome.
2. Lateral Dermatome.
3. Intermediate - Myotome.

25. Surface ectoderm
Neural tube
Dermatome
Somite
Myotome

26. Sclerotome – Cells of the sclerotome migrate medially.
They surround the neural tube and form the vertebral
column
Dermatome – These cells migrate and lie on the deep
surface of the ectoderm.
These give rise to the dermis of skin and
subcutaneous tissue.
Myotome –It gives rise to the striated muscle.
Each myotome is innervated by a spinal nerve.
The number of somites is equal to number of
spinal nerves