Early embryonic development Flashcards
What are egg cells covered in?
The zona pellucida
What is the zona pellucida made of?
Glycoprotein
What is a zygote?
A single cell with genetic information from both the oocyte and sperm
What is cleavage?
Splitting without growth
How many times does cleavage occur?
Until 32 cells within the zona pellucida
What is the name for a 32 cell zygote?
Morula
Does the morula have a zona pellucida?
Yes
What happens to the morula?
Compaction
What is compaction?
The cells of the morula become closer together and the cells on the outside start to differ
When does differentiation first occur?
In the morula
What are the two cell types that first diffferentiate?
Trophoblasts
Embryoblasts
What happens to embryoblasts?
They group at one end forming an inner cell mass
What two structures form inside the trophoblast?
Inner cell mass
Blastocoel
What is a blastocyst?
The name given to the mass of cells that is trophoblasts, inner cell mass and blastocoel
When does the zona pelucida disappear?
Blastocyst formation
What happens to the inner cell mass?
The embryoblast differentiate
Another cavity forms called the amniotic cavity
What is the third differentiated cell types?
Embryo blast forms:
Hypoblast (middle)
Epiblast (around the amniotic cavity)
What prevents polyspermy?
Fast electrical block
Calcium wave causes cortical granules to fuse with the plasma membrane
What is the name of the smaller cells formed by cleavage?
Blastomeres
What forms in compaction?
Tight junctions
When does the embryo implant in the endometrium?
5-6 days after fertilisation
What are the three layers of the uterine wall?
External perimetrium
Medial myometrium
Internal endometrium
How does the uterine wall attach to the blastocyst?
It and the trophoblast both express adhesion molecules
Where does adhesion of the blastocyst occur?
Above the inner cell mass
How does the embryo penetrate the endometrium?
The trophoblast differentiates into cytotrophoblast and synctiotrophoblast
Synctiotrophoblast inserts itself between the uterine and epithelial cells
How does synctiotrophoblast form?
The fusion of cytotrophoblast cells
What does the synctiotrophoblast surround?
With time, the whole embryo, as it embeds in the uterine wall
How long until the embryo is completely embedded in the endometrium?
10 days after fertilisation
What are lacunae?
Formed in the synctiotrophoblast from vacuoles fusing together
What happens at 12 days after fertilisation?
The embryo is totally embedded and uterine epithelial cells have covered the entrance
How does the placenta form?
Lacunae develop into interconnecting network
Synctiotrophoblast penetrates maternal capillaries
What are sinusoids?
Dilated maternal capillaries
What happens after 13 days?
Lacunae and sinusoids fuse
When does the cytotrophoblast proliferate?
13 days
Forms primary villi
What are primary villi?
Contain capillaries and link to the embryonic circulatory system by the connecting stalk
What are tertiary villi?
Form after 21 days
Contain a capillary network connecting embryonic circulation to the umbilical artery and vein
What does the synctiotrophoblast secrete?
hCG
Human chorionic gonadotrophin
