After fertilization, an embryo undergoes three main processes: 1) Cleavage - The zygote rapidly divides through holoblastic or meroblastic cleavage to form a hollow ball of cells called a blastula. 2) Gastrulation - The blastula cells rearrange to form the three germ layers: ectoderm, endoderm, and mesoderm. 3) Organogenesis - The germ layers develop into organs, with the ectoderm forming skin and nervous system, endoderm forming lung, digestive, and glandular tissues, and mesoderm forming muscle and blood tissues.

1. EMBRYONIC DEVELOPMENT
AFTER FERTILIZATION

2. 3 PROCESSES OCCURE IN AN
EMBRYO AFTER FERTILIZATION:
1) Cleavage
2) Gastrulation
3) Organogenesis

3. Cleavage

4. CLEAVAGE
• The single celled zygote undergoes a period of
rapid cell division without growth to produce a
ball of cells.
• A hollow ball of cells are formed called a
blastula.
• The blastula consist of many smaller cells called
blastomeres.
• The blastula has a hollow part that is filled with
fluid and is called a blastocoel.

5. EARLY EMBRYONC DEVELOPMENT
IN ANIMALS

6. BLASTOMERES

7. TWO TYPES OF CLEAVAGE
1) Meroblastic cleavage – this is the incomplete
division of the egg. This occurs in species with
yolk-rich eggs such as reptiles and birds.
Thus only part of the zygote undergoes cleavage
(cell division).
This happens in these eggs due to the large
volume of yolk.

8. 2) Holoblastic cleavage – this is the complete
division of the egg. This occurs in species whose
eggs have small amounts of yolk, such as sea
urchins and frogs.
Thus the entire zygote undergoes cleavage (cell
division).

9. Meroblastic
cleavage
Holoblastic
cleavage

10. GASTRULATION

11. GASTRULATION
Gastrulation is an early embryonic
development in which the cells of a
blastula rearranges into a three-layered
embryo, called a gastrula.

12. THREE EMBRYONIC GERM LAYERS
•Ectoderm
•Endoderm
•Mesoderm

13. ECTODERM
• Ectoderm is the outer layer of the developing
embryo.
It gives rise to:
• Integumentary system
• Brain
• Spinal cord
• Pituitary gland

14. ENDODERM
• Endoderm is the innermost (internal) layer found
in a developing organism.
It gives rise to:
• Epithelial layer of lungs
• Digestive system
• Liver
• Pancreas
• Bladder
• Thyroid glands

15. MESODERM
Mesoderm is the middle layer of the
developing embryo. It is found between
the ectoderm and the endoderm.

17. ORGANOGENESIS

18. ORGANOGENESIS
• Organogenesis is the process of the ectoderm,
endoderm and mesoderm developing into internal
organs of an organism.
• Endoderm: Form tissues within the lungs , thyroid
and pancreas.
• Mesoderm: Assists in the production of cardiac
muscle, skeletal muscles, smooth muscles , tissues
within kidneys and red bloody cells.
• Ectoderm: Makes tissues in the epidermis and
helps in the formation of neurons in the brain and
melanocyte.

20. ORGANOGENESIS CONTINUED….
• In every vertebrates the mesoderm forms the
notochord and the ectoderm forms the neural
plate.
• The neural plate folds inwards and forms a
neural tube which will further go to form the
central nervous system which is the brain and
the spinal cord.

21. FORMATION OF NEURAL CORD
FROM NEURAL PLATE

22. EMBRYONIC DEVELOPMENT PROCESS