Chapter 5 - 3rd Week of Development: Trilaminar Germ Disk

Question 0

When does the gastrulation begin?

Answer 0

It begins with the formation of the primitive streak on the surface of epiblast

Question 1

What happens during gastrulation?

Answer 1

All the three germ layers (ectoderm, mesoderm, endoderm) are established.

Question 2

When is the streak vaguely defined?

Answer 2

day 15-16

Question 3

*Which proteins controls cell invagination in gastrulation?

Answer 3

Fibroblast growth factor 8 (FGF8)

Question 4

Where is fibroblast growth factor 8 (FGF8) synthesized?

Answer 4

It is synthesized by the streak cells

Question 5

How does the FGF8 regulate the cell specifitcation into the mesoderm?

Answer 5

By regulating Brachyury (T) expression

Question 6

What is the source for all germ layers?

Answer 6

The epiblast

Question 7

What happens when the cloacal membrane dissapears?

Answer 7

The posterior wall of the yolk sac forms a small diverticulum that extends into the connecting stalk

Question 8

Primitive node

Answer 8

• Is the cephalic end of the steak.

- Consists of a slightly elevtaed area surrounding the small primitive pit

Question 9

Invagination

Answer 9

Is the migration of the epiblast towards the primitive streak. Upon arrival in the region of the streak, they become flask-shaped, detach from epiblast, and slip beneath it.

Question 10

When does the allantoenteric diverticulum, or allantois, appear?

Answer 10

Around the 16th day of development

Question 11

The cloacal membrane

Answer 11

• Formed at the caudal end of the embryonic disk
• Consists of an endoderm and ectoderm adherent
• No intervenning mesoderm

Question 12

Anterior visceral endoderm (AVE)

Answer 12

• Express genes essential for head formation
• The genes essential for head formation is:
  
  • The transcription factors
    > OTX2
    > LIM1
    > HESX1
  • secreted factors
    > Cerebrus
    > Lefty

Question 13

What inhibits the nodal activity in the cranial end of the embryo?

Answer 13

Cerebru and lefty

Question 14

What maintains and initiate the primitive streak?

Answer 14

The expression of Nodal

Question 15

Nodal is a member of….

Answer 15

Transforming growth factor-B

Question 16

The nodal is responsible….

Answer 16

for formation of dorsal and ventral mesoderm adn head and tail structures

Question 17

Which are members of transforming growth factor?

Answer 17

• Nodal

- Bone morphogenic protein 4 (BMP4)

Question 18

Where can we find Bone morphogenic protein 4 (BMP4)

Answer 18

BMP4 is secreted throughout the embryonic disk

Question 19

Which part of the embryo is the organizer?

Answer 19

The node is the organizer, becuase BMP4 is not blocked by other genes expressed in the node.

Question 20

HNF-3B

Answer 20

Maintains the node adn later induces regional specifity in the forebrain and the midbrain areas

Question 21

Goosecoid

Answer 21

Activates inhibitors of BMP4 contributes to regulation of head development.

Question 22

Brachyury (T) gene

Answer 22

• Control the regulation of dorsal mesoderm formation in middle and caudal regions of the embryo.
• Is essential for cell migration through the primitive streak

Question 23

Where is Brachyury (T) gene expressed?

Answer 23

It is expressed in the node, notochord precusor cells, and notochord.

Question 24

Brachyury

Answer 24

Encodes a sequence-specific DNA binding protein that function DNA binding protein that functions as a transcription factor

Question 25

the T-box

Answer 25

- Is the DNA binding domain. | - Hvae more than 20 genes

Question 26

FG8 maintains...

Answer 26

nodal expression as well as LEFTY-2. And both of these genes upregulate PITX

Question 27

Which homeobox-containing transcription factor is responsible for establishing left sideness?

Answer 27

PITX2

Question 28

Situs inversus and dextrocardia (placement of the heart to the right side) is caused by...

Answer 28

the gene PITX2 being expressed ectopically (e.g on the right side)

Question 29

LEFTY and Sonic hedgehog (SHH)

Answer 29

prevent left sided signals from crossing over

Question 30

Brachyury (T) is essential for expression

Answer 30

of Nodal, LEFTY-1, and LEFTY-2

Question 31

Monoamine oxidase (MAO)

Answer 31

- Breaks down serotonin (5HT) | - Is upstream form FGF8

Question 32

Changes in 5HT signaling result in:

Answer 32

- Setus inversus - Dextrocardia - Other heart defects

Question 33

What does cells that ingress through the cranial region of the node become?

Answer 33

They become the prechordal plate and the notochord

Question 34

What does those cell who migrate at the lateral edges of the node and form the cranial end of the streak become?

Answer 34

They become paraxial mesoderm

Question 35

Cells who migrate trough the midstreak region become...

Answer 35

Intermediated mesoderm

Question 36

Those cells who migrate through the more caudal part of the streak form....

Answer 36

lateral plate mesoderm

Question 37

Where does the cells migrating through the caudalmost part of the streak contribute to?

Answer 37

They contribute to extraembryonic mesoderm

Question 38

What characterize the trophoblast by the beginning of the thrid week?

Answer 38

The trophoblast is characterized by primary villi that cosists of a cytotrophoblastic core covered by a syncytial layer.

Question 39

Secondary villus

Answer 39

Is the structure we get when mesodermal cells penetrate the core of primary villi and grow toward the decidua.

Question 40

When does the mesodermal cells in the core of the villus begin to differentiate into blood cells and small blood vessles?

Answer 40

By the end of third week

Question 41

When do we get the villus capillary system?

Answer 41

By the end of third week, when the mesodermal cells in the core of the villus differentiate into blood cells and small blood vessles.

Question 42

Other names for the villus?

Answer 42

- Tertiary villus | - Definitive placental villus

Question 43

What connects the placenta to the embryo?

Answer 43

- Capillaries in tertiary villi make contact with capillaries developing in the mesoderm of the chorionic plate and in the connecting stalk. - These vessels, in turn, establish contact with the intraembryonic circulatory system

Question 44

When does the heart begins to beat?

Answer 44

- In the 4th week of development

Question 45

When the heart begins to beat....

Answer 45

the villous system is ready to supply the embryo proper essential neutriens and oxygen.