Week 3

Question 1

Day 15-17

Answer 1

▪️gastrulation begins
-formation of primitive streak on Eb dorsal surface
▪️invagination
-inward movement of Eb cells at PS
-undergo epithelial to mesenchymal transition
-detach and slip beneath Eb
▪️tri-laminar disc
-some cells replace Hb and become E-endoderm, those in between become E-mesoderm, those on top become E-ectoderm

Question 2

Day 18-21

Answer 2

▪️NC
-mesenchymal cells migrate cranially from PK to form NC process
-NC process grows cranially until it reaches prechordal plate
-NC process cells detach from endoderm forming a solid cord of cells- NC
-fused layers of ectoderm and endoderm form orophalengeal membrane cranially and cloacal membrane caudally
▪️NC induces thickening of ectoderm forming neural plate

Question 3

Notochord functions

Answer 3

▪️defines axis of the embryo
▪️gives some rigidity
▪️basis for development of axis skeleton
▪️thickening of ectoderm to form neural plate

Question 4

Mesoderm differentiation

Answer 4

▪️NC
▪️paraxial mesoderm 
▪️intermediate mesoderm 
▪️lateral mesoderm 
▪️extra-embryonic mesoderm

Question 5

Gastrulation abnormalities

Answer 5

▪️caudal dysgenesis
-insufficient mesoderm formed in caudal region- problems with lower limbs and urogenital
▪️sacrococcygeal teratomas
-tumours occurs when PS persist