Topic 5: Early Human Development - Embryonic Period and Fetal Period Flashcards
1
Q
What weeks are the embryonic period?
A
- 3rd week to the end of the 8th week
but note that by the zygote stage, it is still an embryo in the first 2 week!
2
Q
What is the purpose of the embryonic period
A
- 3 germ layers are now present, forming the embryo
3
Q
What are the 3 germ layers?
A
1) ectoderm
2) Mesoderm
3) Endoderm
4
Q
How were the germ layers formed?
A
- each layer was formed from mitosis and differentiation of epiblast cells
5
Q
What does the ectoderm form?
A
- the nervous system and epidermis of the skin
6
Q
What does the mesoderm form?
A
- muscles, cardiovascular system, dermis, and most bones
7
Q
What does the endoderm form?
A
- epithelial lining of the digestive, respiratory, urinary, and reproductive system and their associated glands
8
Q
What parts of the embryo have formed in this period?
A
- major organ systems almost completely formed
- heart begins to beat
- limb buds differentiate
- embryonic membranes form
9
Q
As previously stated, embryonic membranes form. Name these membranes. (4)
A
- chorion
- amnion
- yolk sac
- allantois
10
Q
What does the chorion form? (3)
A
- derived from trophoblast cells
- surrounds all embryonic membranes
- chorionic villi
11
Q
What is chorionic villi?
A
projections of the chorion containing the blood vessels that will form the fetal part of the placenta
12
Q
What does the amnion form? (4)
A
- derived from epiblast
- forms the amniotic cavity
- amniotic cavity surrounds embryo/fetus with amniotic fluid
- the fluid’s function is shock absorption, temperature regulation
13
Q
What does the yolk sac form? (4)
A
- derived from hypoblast
- forms part of the GI (gastrointestinal tract)
- produced earliest blood cells and vessels
- source of primordial germ cells
14
Q
What are primordial germ cells?
A
- reporductive cells composed of primary oocytes and primary spermatocytes
15
Q
How many weeks does the fetal period span?
A
- 9th to end of the 40th week
