5. First weeks of development

Question 1

Fertilization vs gestation

Answer 1

40 weeks after last period
38 weeks post-fertilization
40 weeks gestation

Question 2

Maturation of follicle

Answer 2

Ovulation –> corpus luteum

Question 3

Implantation

Answer 3

6-7 days pf
Attachment to blastocyst to endometrium
Formation of vital embryonic structures
Inner cell mass growing rapidly (new layer)
Trophoblast cells create outer cynytial layer and synthesize human chorionic gonadotropin hormone (hCG): signals to corpus luteum to increase size and progesterone production
ICM forms amniotic cavity and makes hypoblast next to epiblast

Question 4

Gastrulation

Answer 4

Invagination
Making endoderm ectoderm and mesoderm
Maternal blood supply by lacunae
Hypoblast of ICM forms (fake) endoderm
Epiblast of ICM separates from trophoblast (germinal disc, primary ectoderm)
Upper ICM will form amnion

Question 5

Week of 2’s

Answer 5

2 cell types: trophoblasts, cyncytial
2 layers: hypoblast and epiblast
2 cavities: amnion and chorion
2 extraembryonic membranes: mesoderm and chorion

Question 6

2nd week

Answer 6

Enzymatic destruction
Implantation at embryonic vegetal pole (ICM side)
Syncytiotrophoblasts destroy endometrium glands and vessels, cover more of embryo
Glycogen and lipids are released and diffuse to embryo
Clear presence of amniotic cavity (almost germinal disc, amnion)
Hypoblast start moving (first part of yolk sac)
Everything is covered in mesoderm

Question 7

Implantation at embryonic vegetal pole (ICM side)

Answer 7

Orientation by specific factors
Endothelial growth factor receptor

Question 8

Chorionic cavity formation

Answer 8

Emnion + embryonic disc + yolk sac connected to mesoderm by connecting stalk
Hypoblast migration to form Heuser’s membrane (primary yolk sac)
Extraembryonic mesoderm forms material between Heuser’s membrane and cytotrophoblasts
Extraembryonic mesoderm between amnion and cytotrophoblasts
Extraembryonic mesoderm splits into 2, leaving cavity: chorion
Second wave of hypoblast cell migration

Question 9

Second wave of hypoblast cell migration

Answer 9

Endoderm migrates over mesoderm
Secondary yolk sav
Primary yolk sac is pushed forward
Remnants go to vegative pole (chorionic cavity)

Question 10

Placentation

Answer 10

Occurs as blood vessels form around periphery of blastocyst

Question 11

Ectopic implantation

Answer 11

Risk to mother and child
Can happen in abdomen, fallopian tube and uterus