Fertilization and Embryonic Development

Fertilization takes place in the fallopian tube

The fertilized egg is called a zygote

The fertilized egg undergoes a series of mitotic cell divisions called cleavage Once cleavage takes place the zygote is called an embryo

During cleavage the number of cells increases, but not the size of the developing embryo

Stages of Embryonic Development The morula is the stage of development when the embryo is a mass of cells formed from cleavage

Stages of Embryonic Development In the blastula stage the embryo is a hollow ball made of a single layer of cells( it is the same size as the zygote)

Implantaton occurs during the blastula stage 6 to 10 days after fertilization

During the gastrula stage, one side of the blastula becomes indented forming an inner and outer layer of cells (same size as the zygote)

Three germ layers are formed Three germ layers are formed. All tissues and organs form from these layers

The ectoderm – is the outer layer It becomes the nervous system and the skin

The mesoderm is the middle layer It becomes muscles, skeleton, circulatory, excretory and reproductive systems

The endoderm is bottom layer It becomes the liver, pancreas, digestive and respiratory systems

Differentiation is the process by which the primary germ layers cells become specialized into various tissues and organs

Cells not only increase in number but size increases as well