Embryonic Development Fertilization Each month an egg matures

Embryonic Development

Fertilization • Each month an egg matures and is released from the ovary during ovulation. • The egg enters the fallopian tube. • It is in the fallopian tube where sperm must encounter the egg. • Sperm fuses with the egg in a process called fertilization.

http: //www. daviddarling. info/images/Fallopian_tube. gif

Early Development • The fertilized egg is called a zygote. • The zygote begins to undergo mitotic cell division called cleavage. • Eventually a ball of cells called a morula is formed. http: //www. biology. iupui. edu/biocourses/n 100/images/38 cleavage. jpg

The Blastula Stage • After the 5 days the morula has continued to undergo cell division and forms a hollow ball of cells called the blastula (aka blastocyst) http: //www. ehponline. org/members/2006/114 -11/blastocyst. jpg

Implantation • When the blastula reaches the uterus it becomes embedded in the uterine lining. • This is called implantation and signifies the beginning of pregnancy. http: //www. dkimages. com/discover/previews/940/674676. JPG

Gastrulation • Gastrulation involves the inward migration of cells of the blastula. • This in-folding creates a layered structured called the gastrula. • Some migratory cells break off and form a third layer of cells. • The three layers of cells are called germ layers and will eventually form certain organs.

http: //trc. ucdavis. edu/biosci 10 v/bis 10 v/week 10/gastrulation. gif

The Germ Layers • The inner layer is called the endoderm. • The middle layer is the mesoderm. • The outer layer is the ectoderm.

Germ Layer Fate Endoderm Becomes the digestive tract and associated organs Mesoderm Becomes the muscles and bones Ectoderm Becomes the skin and nervous system