Early Embryology Flashcards
What does the embryo enter the uterine cavity as 3 days after fertilization?
Morula
What does the morula become by swelling with fluid?
Blastocyst–> formed in the 1st week; called blastocyst when it forms an inner cell mass
*What two structures compose the blastocyst?
- Embryoblast (forms embyro)
2. Trophoblast (forms placenta)
What two structures develop from the trophoblast? When?
- Cytotrophoblast
- Syncytiotrophoblast
* in the 2nd week
What does the cytotrophoblast form?
Primary villi
What does the syncytiotrophoblast do?
Implants into the uterine wall and actually produces hCG–> is the outer portion of the trophoblast
In the second week, what two layers comprise the embryo?
Epiblast and hypoblast (called bilaminar disk)–> is composed of two germ layers at this point
What germ layer does the epiblast give rise to?
ectoderm
What structure does mesoderm and endoderm derive from?
primitive streak
What two cavities are present in the second week?
- amniotic cavity
2. yolk sac
*Rule of 2’s (3 rules)
In the 2nd week:
- 2 germ layers (bilaminar disc; epiblast, hypoblast)
- 2 cavities (amniotic cavity, yolk sac)
- 2 components to placenta (syncytio- and cytotrophoblast)
Rule of 3’s (1 rule)
3 germ layers in the third week (endoderm, ectoderm, mesoderm)–> process of obtaining the three layers is called gastrulation; cells called gastrula in the 3rd week
What week does neural tube form and close?
4th week
What weeks does organogenesis take place?
Weeks 3-8; called embryonic period
When does implantation occur?
By the 7th day
