EMBRYONIC DEVELOPMENT AFTER FERTILIZATION

3 PROCESSES OCCURE IN AN EMBRYO AFTER FERTILIZATION:

1) Cleavage

2) Gastrulation

3) Organogenesis

Cleavage

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.

EARLY EMBRYONC DEVELOPMENT IN ANIMALS

BLASTOMERES

TWO TYPES OF CLEAVAGE1) 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.

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).

Meroblastic cleavage

Holoblastic cleavage

GASTRULATION

GASTRULATION

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

THREE EMBRYONIC GERM LAYERS

•Ectoderm

•Endoderm

•Mesoderm

ECTODERM

•Ectoderm is the outer layer of the developing embryo.

It gives rise to:• Integumentary system•Brain•Spinal cord•Pituitary gland

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

MESODERMMesoderm is the middle layer of the developing embryo. It is found between the ectoderm and the endoderm.

ORGANOGENESIS

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.

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.

FORMATION OF NEURAL CORD FROM NEURAL PLATE

EMBRYONIC DEVELOPMENT PROCESS