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Body Logistics > Embryology 1 > Flashcards

Embryology 1 Flashcards

1
Q

What are the three periods from fertilisation until birth?

A

Pre-embryonic
Embryonic
Fetal

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2
Q

What is the pre-embryonic period? Name the three steps.

A

The first two weeks of development

  1. Cleavage (formation of morula)
  2. Compaction (formation of blastocyst)
  3. Implantation begins
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3
Q

Briefly outline fertilisation.

A
  1. An oocyte is released from the ovary.
  2. Travels along the Fallopian tube
  3. Here in the Fallopian tube in the ampulla it is fertilised by the sperm
  4. The fertilised oocyte is called the zygote.
  5. Implantation occurs
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4
Q

What is the ideal site for implantation?

A

The posterior uterine wall.

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5
Q

What happens after the zygote is formed, and what is the product called?

A

Cleavage and this results in 2 blastomeres of equal size. Also the zona pellucida is formed.

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6
Q

What is the zona pellucida?

A

A glycoprotein shell that prevents further sperm to try to fertilise the oocyte.

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7
Q

What happens after the 2 blastomeres are formed?

A

The blastomeres continue to divide into 4 upto 8 cells to form a morula. This is called the cleavage.

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8
Q

Why is the morula important?

A

Because it is totipotent. This means that it has the capacity to become any cell.

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9
Q

How does the morula relate to in vitro fertilisation.

A

The oocyte is fertilised and allowed to develop into a morula, then it is transferred into the uterus.
Pre-implantation genetic diagnosis can be used to safely remove a cell from the morel to test for heritable conditions prior to transfer the embryo into the mother.

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10
Q

Where does the sperm fertilise the oocyte?

A

In the ampulla of the Fallopian tube.

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11
Q

What is the fertilised oocyte called?

A

A zygote

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12
Q

What is the divided zygote called?

A

Blastomeres

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13
Q

What happens after the formation of the morula?

A

This step is called compaction which is the formation of first cavity and thereof a blastocyst.

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14
Q

What is the inner cell mass in the blastocyst called?

A

Embryoblast

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15
Q

What is the outer cell mass that lines the blastocyst cavity called?

A

Trophoblast

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16
Q

What happens after compaction regarding the potency of the cells?

A

From being totipotent the cells are now only pluripotent. This means that they can’t differentiate into all cells but still many cells.

17
Q

What happens after compaction?

A

Hatching where the zona pellucida is broken down.

18
Q

What are the two most important consequences of the breakdown of the zona pellucida?

A

The blastocyst is free to enlarge now.

It can also interact with the uterine surface to implant itself.

19
Q

What happens following the hatching?

A

Implantation of the blastocyst.

20
Q

Briefly outline the process of fertilisation to implantation.

A

Zygote is formed. Divide into two to form 2 blastomeres, the zona pellucida also forms here.
Cleavage occurs to form the morula (4-8 cells)
After this compaction occur where a blastocyst is formed and the first cavity is formed as well.
Hatching occurs which breaks down the zona pellucida rendering the blastocyst able to enlarge and implant into the (favourably the) posterior uterine wall.

21
Q

What happens during week 2?

A

Differentiation into two distinct cellular layers.

22
Q

What two distinct cellular layers emerge?

A

An outer cell mass and an inner cell mass.

23
Q

What are the two parts of the outer cell mass?

A

Syncytiotrophoblasts

Cytotrophoblasts

24
Q

What are the two parts of the inner cell mass?

A

Epiblasts

Hypoblasts

25
Q

What is the bilaminar disc?

A

The two-layered disc that consists of epiblasts and hypoblasts.

26
Q

What is the amniotic cavity?

A

A cavity lined by epiblasts.

27
Q

Why is the implantation so important?

A

It establishes maternal blood flow within the placenta to allow the embryo to be supported from maternal circulation.
It establishes the basic structural unit of matron-fetal exchange of nutrients.

28
Q

Give two example of conditions linked to implantation defect.

A

Placenta praevia

Ectopic pregnancy

29
Q

What is ectopic pregnancy?

A

When implantation has occurred anywhere else but the uterine wall. This can be life threatening very quickly.

30
Q

What is placenta praevia?

A

When implantation occurs in the lower uterine segment.

This can cause haemorrhage in pregnancy and requires C-section delivery.

31
Q

Where can embryonic pole be found? What happens here after implantation?

A

Above the amniotic cavity and the epiblasts as well as the cytotrophoblasts. This is faced away from the uterine wall.
Here occurs rapid development of syncytiotrophoblasts which proliferate quickly.

32
Q

Where can the abembryonic pole be found? What happens here after implantation?

A

The part closest to the uterine wall. Here the primitive yolk sac is formed.

33
Q

What happens after the proliferation of syncytiotrophoblasts and the formation of the yolk sac?

A

The yolk sac is pushed away from the cytotrophoblasts and a reticulum is formed. This reticulum is later converted into extra embryonic mesoderm.

34
Q

After this there is an important step occurring. Briefly outline it.

A

Syncytiotrophoblasts invade the maternal sinusoids. This establishes a uteroplacental circulation in order for the embryo to be able to take use of the maternal blood circulation.

35
Q

What is the next step?

A

Formation of a secondary yolk sac which is pinched off from the primitive yolk sac.

36
Q

Now by the end of the second week, what does the embryo look like?

A

From in to out.
The bilaminar disc consisting of epiblasts (upper) and hypoblasts (lower).
The epiblasts line the amniotic cavity.
The hypoblasts line the yolk sac.
This formation is found surrounded by the chorionic cavity.
The chorionic cavity is lined by the cytotrophoblasts which in their turn are lined by syncytiotrophoblasts that have invaded the maternal sinusoids.

37
Q

Why are the cytotrophoblasts and syncytiotrophoblasts important?

A

Because they form placental membranes.

38
Q

Why are the epiblasts and hypoblasts important?

A

Because they form the bilaminar disc that will become the foetus eventually.

Body Logistics (21 decks)

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