Chp#5 Third Week Of Development

Question 1

Most characteristic event occur in which week ?

Answer 1

3rd week of gestation

Question 2

What is the 3rd week of gestation called ?

Answer 2

Gastrulation period

Question 3

What happens in this week ?

Answer 3

3 germ layers are formed endo, meso and ecto

Question 4

How does this week begins?

Answer 4

Begins with the formation of primitive streak on the surface of the epiblast

Question 5

In what day narrow groove is visible?

Answer 5

In 15 to 16 day embryo narrow groove is visible with slightly bulging regions on either side

Question 6

What is cephalic end of streak called ?

Answer 6

Primitive node, consists of a slightly elevated area surrounding the small primitive pit.

Question 7

Where do the cells of epiblast migrate?

Answer 7

Towards the primitive streak

Question 8

What shape forms upon the arrival of the cells in the region of streak?

Answer 8

They become flask shaped l, detach from epiblast and slip beneath it

Question 9

Inward movement is called

Answer 9

Invagination

Question 10

Cell migration and specification is controlled by

Answer 10

Fibroblast growth factor 8 (FCF8) synthesized by streak cells themselves

Question 11

Function of FGF8

Answer 11

Controls cell movement by down regulating E-cadherin

Controls cell specification into mesoderm by regulating BRACHYURT (T) expression

Question 12

What is E-cadherin

Answer 12

A protein that normally binds epiblast cells together

Question 13

What do cells do after invaginatiom

Answer 13

Displace hypoblast creating embryonic endoderm, others come to lie between the epiblast and newly created the endoderm to form mesoderm

Question 14

What do the cells remaining in the epiblast do

Answer 14

Form ectoderm

Question 15

Source of all the germ layers?

Answer 15

Epiblast through the process of gastrulation

Question 16

What happens to the cells when more of them move b/w epiblast and hypoblast layers ?

Answer 16

Spread laterally and cranially gradually migrating beyong the margin of the disc and establishing contact with extraembryonic mesoderm covering the yolk sac and amnion.

Question 17

What happens in cephalic direction

Answer 17

They pass on each side of the prechordal plate

Question 18

Where Prechordal plate forms

Answer 18

Between the tip of the notochord and oropharyngeal membrane

Question 19

Prechordal plate derived from

Answer 19

Some of the first cells that migrate through the node in the midline and move in a cephalic direction

Question 20

Prechordal plate imp for

Answer 20

Induction of the forebrain

Question 21

Ororpharyngeal membrane consists of

Answer 21

A small region of tightly adherent ectoderm and endoderm cells that represents the future opening of the oral cavity.

Question 22

Which cells invaginate in the primitive node?

Answer 22

Prenotochordal cells invaginating in primitive node move forward cranially in the midline until they reach the prechordal plate. these prenotochordal cells become intercalated in the hypoblast so that for a short time the midline of embryo consists of 2 cells layers

Question 23

Midline of embryo consists of 2 cell layers that form

Answer 23

Notochordal plate

Question 24

When notochordal plate proliferate and detach from the endoderm

Answer 24

When hypoblast is replaced by the endoderm cells moving in at the streak

Question 25

Cells of notochordal plate form a solid cord of cells called

Answer 25

Definitive notochord

Question 26

What is definitive notochord

Answer 26

Which Underlies the neural tube and is a signaling center for inducing the axial skeleton

Question 27

Which process is elongation of notochord

Answer 27

Dynamic process teh cranial end forms first and caudal regions are added as the primitive streak assume a more caudal position

Question 28

How notochord and prenotochordal cells extend

Answer 28

Cranially to prechordal plate (an area just caudal to the oropharyngeal membrane) and caudally to primitive pit.