DONE Embryology Flashcards
What is the pre-embryonic period?
1st 2 weeks of development
- Cleavage (forms morula)
- Compaction (forms blastocyst)
- Implantation
Where is the sperm fertilised?
Ampulla of Fallopian tube
Where is the ideal site for implantation?
Posterior uterine wall
What is cleavage?
In week 1
Mitotic divisions = 2 blastomeres of equal size
Zona pellucida forms
What is a morula?
When compacted blastomeres divide to form 16-cell (each cell totipotent) morula
What is compaction?
In week 1
Formation of 1st cavity + blastocyst
Segregates inner + outer cells
In a blastocyst, after compaction, what is the trophoblast?
Outer cell mass, forms epithelial wall, contributes to placenta
In a blastocyst, after compaction, what is the embryoblast?
Inner cell mass, form embryo
After compaction are the cells pluripotent, totipotent or multipotent?
Pluripotent (can become many cell types)
What is hatching?
Week 1
Blastocyst hatches from zona pellucida after compaction for implantation
How many cells does the blastocyst have at start of implantation?
100 cells, 8 make embryo, rest form fetal membranes
Where does implantation begin?
Blastocyst implants into uterine epithelium (endometrium)
What occurs in the week of twos?
2 cellular layers emerge from the outer cell mass + inner cell mass
In the week of twos what does the outer cell mass form?
Syncytiotrophoblast = multi-nucleated epithelial, transport between mother + embryo Cytotrophoblast = inner layer mononucleated cells
In the week of twos what does the inner cell mass form?
The bilaminar disc:
- Epiblast = columnar cells next to amniotic cavity
- Hypoblast = cuboidal cells next to blastocyst cavity
By the end of 2nd week, what has occurred?
Conceptus has implanted
Embryo + its 2 cavities (amniotic + yolk sac) suspended (by connecting stalk) within supporting sac (chorionic cavity)
What does implantation allow?
Link between maternal + fetal circulation into placenta (chorionic villus)
What are the 2 implantation defects?
Ectopic pregnancy = implantation not in uterine body (mainly in fallopian tube), life-threatening
Placenta praevia = implantation in lower uterine segment, haemorrhage, C-section
What occurs in week 2, day 9?
Syncytiotrophoblast form lacunae (gaps)
Primitive yolk sac forms
What occurs in week 2, day 11?
Primitive yolk sac membrane pushed away from cytotrophoblast, converted to extraembryonic mesoderm
What occurs in week 2, day 12?
Maternal sinusoids (capillaries) invaded by syncytiotrophoblast Uteroplacental circulation begins
What occurs in week 2, day 13?
Secondary yolk sac forms
What occurs in week 2, day 14?
Chorionic cavity forms
Embryo suspended by connecting stalk (column of mesoderm, future umbilical cord)
Bleeding can be confused with menstrual (increased blood flow to lacunar spaces)
Early pregnancy loss
50% zygotes lost in 1st 2-3 weeks
15% pregnancies miscarry
1% women have recurrent miscarriages (3 consecutive pregnancies)
