Early Embryonic development 2 Flashcards Preview

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Flashcards in Early Embryonic development 2 Deck (33)
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0
Q

What is gastrulation?

A

-The process of forming all three germ layers from the epiblast

1
Q

What are the main events which occur in week 3 of development?

A
  • Gastrulation

- Defining of the axes

2
Q

What is the first event in gastrulation?

A

-Formation of the primitive streak

3
Q

Where does the primitive streak form?

A

-In any direction on the surface of the epiblast

4
Q

What is the structure of the primitive streak?

A
  • A streak of cells which appears on the surface of the epiblast which has narrow bulging at the edges
  • The primitive node is an elevated area located at the cranial end of the streak
  • The primitive pit is a central depression in the node
5
Q

What is the first event that occurs involving the primitive streak?

A

-Invagination-> cells of the epiblast migrate towards the streak, detach from the epiblast and depress down into the streak

6
Q

What does the process of invagination into the primitive streak cause?

A

-Displacement of the hypoblast by the differentiated cells of the epiblast known as endoderm

7
Q

What happens to the primitive streak as invagination is occuring?

A

-Begins to regress towards the caudal end

8
Q

How are the mesoderm and ectoderm layers formed during gastrulation?

A

-Once the endoderm has formed, the epiblast cells begins to diferentiate into ectoderm, whilst invagination of epiblast cells which are differentiating to mesoderm fills the space inbetween the two layers

9
Q

What happens to the primitive yolk sac during gastrulation?

A

-The hypoblast regresses and endoderm now lines the primitive yolk sac

10
Q

What is the end result of gastrulation?

A

-Formation on the trilaminar disc containing the three germ layers

11
Q

Does mesoderm fill the entire space between the ectoderm and endoderm?

A

-Yes, except from 2 areas, one at the cranial end and one at the caudial end which will be the future mouth and anus

12
Q

How are the openings for the mouth and anus produced?

A
  • These areas are not filled with mesoderm which gives rise to the CVS
  • Without CVS these areas will die and rupture creating openings
13
Q

What is the notochord?

A

-A solid rod of cells which runs down the midline of the trilaminar disc

14
Q

How is the notochord formed?

A

-Cells migrate from the primitive node and form a line down the midline without spreading out

15
Q

What two events does the notochord permit?

A
  • Defining of the axes

- Formation of the nervous system

16
Q

In what direction does the notochord form?

A

-Cranial to caudal

17
Q

Which event defines the formation of the cranial/caudal axes?

A

-Formation of the primitive streak

18
Q

Which axes does the notochord define?

A
  • Dorso-ventral

- left-right

19
Q

How does the notochord define the left-right axes

A

-Signals for the beating action of cilia which produce a side-specific signalling cascade

20
Q

What is situs invertus and what causes it to occur?

A
  • Complete mirror image of the organs and structures of the body-> often not associated with morbidity
  • Immotile cilia
21
Q

What are the derivatives of ectoderm?

A
  • Organs and structures which remain in contact with the outside world
  • Epidermis
  • Nervous system
22
Q

What are the derivatives of mesoderm?

A
  • Supporting structures

- CVS, muscles, bone, cartilage

23
Q

What are the derivatives of the endoderm?

A
  • Internal structures
  • Epithelia of the GI tract and respiratory tract
  • Parenchymal cells
24
Q

What are the three possible causes of monozygotic twins?

A
  • Zygote separates at two cell stage
  • Zygote separates at the inner cell mass
  • Appearance of second primitive streak
25
Q

In twinning, why do two embryos have two placentas is separation occurs at the two cell stage?

A

-Embryo has split before any differentiation, meaning that each ambryo can then differentiate to produce a placenta of their own

26
Q

In twinning, if separation occurs at the inner cell mass, why are two embryos produced which share a placenta?

A
  • The embryo has undergone differentiation into inner cell mass and outer cell mass
  • Outer cell mass forms placenta, separation of the inner cell mass inside the outercell mass will produce two embryos sharing a placenta
27
Q

In twinning, why does the appearance of another primitive streak lead to embryos sharing an amniotic cavity?

A

-The primitive streak appears on the epiblast which lies inside of the amniotic cavity which has already developed

28
Q

In twinning, when can the appearance of a second primitive streak produce conjoined twins?

A

-If separation (of the bilaminar disc) is not complete

29
Q

What is teratogenesis?

A

-The disruption of embryonic development by whatever means

30
Q

Why does each organ system have a particularly sensitive window for teratogenesis?

A

-They all develop at different times

31
Q

Give an example of a chemical teratogenic agent

A
  • Thalidomide
  • Alchol
  • Drugs
32
Q

Give an example of an infectious teratogenic agent

A

-Rubella