Early Embryonic development 2 Flashcards Preview

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

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

-Gastrulation
-Defining of the axes

1

What is gastrulation?

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

2

What is the first event in gastrulation?

-Formation of the primitive streak

3

Where does the primitive streak form?

-In any direction on the surface of the epiblast

4

What is the structure of the primitive streak?

-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

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

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

6

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

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

7

What happens to the primitive streak as invagination is occuring?

-Begins to regress towards the caudal end

8

How are the mesoderm and ectoderm layers formed during gastrulation?

-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

What happens to the primitive yolk sac during gastrulation?

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

10

What is the end result of gastrulation?

-Formation on the trilaminar disc containing the three germ layers

11

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

-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

How are the openings for the mouth and anus produced?

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

13

What is the notochord?

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

14

How is the notochord formed?

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

15

What two events does the notochord permit?

-Defining of the axes
-Formation of the nervous system

16

In what direction does the notochord form?

-Cranial to caudal

17

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

-Formation of the primitive streak

18

Which axes does the notochord define?

-Dorso-ventral
-left-right

19

How does the notochord define the left-right axes

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

20

What is situs invertus and what causes it to occur?

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

21

What are the derivatives of ectoderm?

-Organs and structures which remain in contact with the outside world
-Epidermis
-Nervous system

22

What are the derivatives of mesoderm?

-Supporting structures
-CVS, muscles, bone, cartilage

23

What are the derivatives of the endoderm?

-Internal structures
-Epithelia of the GI tract and respiratory tract
-Parenchymal cells

24

What are the three possible causes of monozygotic twins?

-Zygote separates at two cell stage
-Zygote separates at the inner cell mass
-Appearance of second primitive streak

25

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

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

26

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

-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

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

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

28

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

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

29

What is teratogenesis?

-The disruption of embryonic development by whatever means

30

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

-They all develop at different times

31

Give an example of a chemical teratogenic agent

-Thalidomide
-Alchol
-Drugs

32

Give an example of an infectious teratogenic agent

-Rubella