Early embryonic development Flashcards

1
Q

What are egg cells covered in?

A

The zona pellucida

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2
Q

What is the zona pellucida made of?

A

Glycoprotein

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3
Q

What is a zygote?

A

A single cell with genetic information from both the oocyte and sperm

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4
Q

What is cleavage?

A

Splitting without growth

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5
Q

How many times does cleavage occur?

A

Until 32 cells within the zona pellucida

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6
Q

What is the name for a 32 cell zygote?

A

Morula

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7
Q

Does the morula have a zona pellucida?

A

Yes

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8
Q

What happens to the morula?

A

Compaction

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9
Q

What is compaction?

A

The cells of the morula become closer together and the cells on the outside start to differ

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10
Q

When does differentiation first occur?

A

In the morula

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11
Q

What are the two cell types that first diffferentiate?

A

Trophoblasts

Embryoblasts

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12
Q

What happens to embryoblasts?

A

They group at one end forming an inner cell mass

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13
Q

What two structures form inside the trophoblast?

A

Inner cell mass

Blastocoel

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14
Q

What is a blastocyst?

A

The name given to the mass of cells that is trophoblasts, inner cell mass and blastocoel

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15
Q

When does the zona pelucida disappear?

A

Blastocyst formation

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16
Q

What happens to the inner cell mass?

A

The embryoblast differentiate

Another cavity forms called the amniotic cavity

17
Q

What is the third differentiated cell types?

A

Embryo blast forms:
Hypoblast (middle)
Epiblast (around the amniotic cavity)

18
Q

What prevents polyspermy?

A

Fast electrical block

Calcium wave causes cortical granules to fuse with the plasma membrane

19
Q

What is the name of the smaller cells formed by cleavage?

A

Blastomeres

20
Q

What forms in compaction?

A

Tight junctions

21
Q

When does the embryo implant in the endometrium?

A

5-6 days after fertilisation

22
Q

What are the three layers of the uterine wall?

A

External perimetrium
Medial myometrium
Internal endometrium

23
Q

How does the uterine wall attach to the blastocyst?

A

It and the trophoblast both express adhesion molecules

24
Q

Where does adhesion of the blastocyst occur?

A

Above the inner cell mass

25
How does the embryo penetrate the endometrium?
The trophoblast differentiates into cytotrophoblast and synctiotrophoblast Synctiotrophoblast inserts itself between the uterine and epithelial cells
26
How does synctiotrophoblast form?
The fusion of cytotrophoblast cells
27
What does the synctiotrophoblast surround?
With time, the whole embryo, as it embeds in the uterine wall
28
How long until the embryo is completely embedded in the endometrium?
10 days after fertilisation
29
What are lacunae?
Formed in the synctiotrophoblast from vacuoles fusing together
30
What happens at 12 days after fertilisation?
The embryo is totally embedded and uterine epithelial cells have covered the entrance
31
How does the placenta form?
Lacunae develop into interconnecting network | Synctiotrophoblast penetrates maternal capillaries
32
What are sinusoids?
Dilated maternal capillaries
33
What happens after 13 days?
Lacunae and sinusoids fuse
34
When does the cytotrophoblast proliferate?
13 days | Forms primary villi
35
What are primary villi?
Contain capillaries and link to the embryonic circulatory system by the connecting stalk
36
What are tertiary villi?
Form after 21 days | Contain a capillary network connecting embryonic circulation to the umbilical artery and vein
37
What does the synctiotrophoblast secrete?
hCG | Human chorionic gonadotrophin