Trilaminar Germ Disc

Question 1

Steps of Gastrulation

Answer 1

1. Primitive Streak formation:
   - >Primitive node on EPIBLAST signals streak formation
2. Invagination
   - ->folding in creates endoderm
3. Invagination continues creating Mesoderm (somatic cells)
4. Remaing Epiblast cells form ectoderm
5. Notochord formation
   - ->prenotochordal cells pass through streak going from hypo to endo to meso derm

Question 2

Anterior Visceral Endoderm

Answer 2

signals genes for head formation. established before gastrulation

Question 3

GF beta

Answer 3

est. cranial end/maintains notochord

Question 4

BMP-4

Answer 4

GF secreted during BILAMINAR as MESODERM is forming to create intermediate and lateral mesoderm
–>VENTRILIZES

Question 5

Formation of the notochord

Answer 5

1. prenotochord cells pass through primitive streak to establish notochordal plate to intercalate the endoderm
2. notochordal plate separates from endoderm (which replays hypoblast as bottom layer)`

Question 6

Chordin

Answer 6

Activated by Goosecoid.
–>Noggin and Follistatin (secreted by node)

• -> all, antagonize BMP-4.
• ->DORSALIZES MESODERM

Question 7

Noggin and Follistatin secreted by Notochord:

Answer 7

create neural induction in cranial region

Question 8

Brachyury T gene product

Answer 8

DORSALIZES mesoderm

Question 9

placental villus

outward to inward

Answer 9

3rd week: Primary villi
-->2 trophoblastic layers
Secondary Villus:
-->extraembryonic MESODERM core
Tertiary villus
-->trophoblastic layers depleated
-->fetal capillaries from mesoderm go through connecting stalk and chorionic plate to contact villus capillaries