Early Embryonic Development (Lec 5)

Question 1

Contributions to Zygote

Answer 1

Female: 1 nucleus (23 chromosomes), large amount of cytoplasm (mitochondria, granules, mRNA, ribosomes

Male: 1 nucleus (23 chromosomes), very little amount of mitochondria

Question 2

Morula

Answer 2

> 16 cells after 72hours (still surrounded by Zona Pellucida)

Question 3

Hatching

Answer 3

Shedding of Zona Pellucida from Morula

Question 4

Blastocyst

Answer 4

~100 cells

• Inner cell mass: becomes extraembryonic disc
• Trophoblast: becomes chorion -> placenta
• Blastocoel: fluid-filled cavity

Question 5

Implantation

Answer 5

Begins day 6-7
- Cytotrophoblast: inner layer of cells
- Syncytiotrophoblast: outer layer of cells, aids in adhesion into endometrial wall
Implantation complete by Week 2

Question 6

Implantation Hormones

Answer 6

Human Chorionic Gonadotropin (hCG):

• Secreted by Trophoblast cells (later by Chorion)
• Maintains Corpus Luteum to prevent menstruation and continues secretion of Progesterone/Estrogen
• hCG levels decline as placenta forms