1. Fertilization and Embryonic Development

2. Fertilization takes place in the fallopian tube

3. The fertilized egg is called a zygote

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

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

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

8. 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)

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

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

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

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

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

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

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

16. Cells not only increase in number but size increases as well