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

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

0
Q

When does the gastrulation begin?

A

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

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1
Q

What happens during gastrulation?

A

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

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2
Q

When is the streak vaguely defined?

A

day 15-16

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3
Q

*Which proteins controls cell invagination in gastrulation?

A

Fibroblast growth factor 8 (FGF8)

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4
Q

Where is fibroblast growth factor 8 (FGF8) synthesized?

A

It is synthesized by the streak cells

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5
Q

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

A

By regulating Brachyury (T) expression

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6
Q

What is the source for all germ layers?

A

The epiblast

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7
Q

What happens when the cloacal membrane dissapears?

A

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

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8
Q

Primitive node

A
  • Is the cephalic end of the steak.

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

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9
Q

Invagination

A

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.

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10
Q

When does the allantoenteric diverticulum, or allantois, appear?

A

Around the 16th day of development

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11
Q

The cloacal membrane

A
  • Formed at the caudal end of the embryonic disk
  • Consists of an endoderm and ectoderm adherent
  • No intervenning mesoderm
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12
Q

Anterior visceral endoderm (AVE)

A
  • Express genes essential for head formation
  • The genes essential for head formation is:
    • The transcription factors
      > OTX2
      > LIM1
      > HESX1
    • secreted factors
      > Cerebrus
      > Lefty
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13
Q

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

A

Cerebru and lefty

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14
Q

What maintains and initiate the primitive streak?

A

The expression of Nodal

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15
Q

Nodal is a member of….

A

Transforming growth factor-B

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16
Q

The nodal is responsible….

A

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

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17
Q

Which are members of transforming growth factor?

A
  • Nodal

- Bone morphogenic protein 4 (BMP4)

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18
Q

Where can we find Bone morphogenic protein 4 (BMP4)

A

BMP4 is secreted throughout the embryonic disk

19
Q

Which part of the embryo is the organizer?

A

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

20
Q

HNF-3B

A

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

21
Q

Goosecoid

A

Activates inhibitors of BMP4 contributes to regulation of head development.

22
Q

Brachyury (T) gene

A
  • Control the regulation of dorsal mesoderm formation in middle and caudal regions of the embryo.
  • Is essential for cell migration through the primitive streak
23
Q

Where is Brachyury (T) gene expressed?

A

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

24
Q

Brachyury

A

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

25
Q

the T-box

A
  • Is the DNA binding domain.

- Hvae more than 20 genes

26
Q

FG8 maintains…

A

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

27
Q

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

A

PITX2

28
Q

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

A

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

29
Q

LEFTY and Sonic hedgehog (SHH)

A

prevent left sided signals from crossing over

30
Q

Brachyury (T) is essential for expression

A

of Nodal, LEFTY-1, and LEFTY-2

31
Q

Monoamine oxidase (MAO)

A
  • Breaks down serotonin (5HT)

- Is upstream form FGF8

32
Q

Changes in 5HT signaling result in:

A
  • Setus inversus
  • Dextrocardia
  • Other heart defects
33
Q

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

A

They become the prechordal plate and the notochord

34
Q

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

A

They become paraxial mesoderm

35
Q

Cells who migrate trough the midstreak region become…

A

Intermediated mesoderm

36
Q

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

A

lateral plate mesoderm

37
Q

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

A

They contribute to extraembryonic mesoderm

38
Q

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

A

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

39
Q

Secondary villus

A

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

40
Q

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

A

By the end of third week

41
Q

When do we get the villus capillary system?

A

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

42
Q

Other names for the villus?

A
  • Tertiary villus

- Definitive placental villus

43
Q

What connects the placenta to the embryo?

A
  • 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
44
Q

When does the heart begins to beat?

A
  • In the 4th week of development
45
Q

When the heart begins to beat….

A

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

Embryology (9 decks)

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