LEC 14: Embryology III - 08.26.14

Question 1

gastrulation

Answer 1

formative process by which the three (3) germ layers and axial orientation are established in embryos

Question 2

When does gastrulation begin

Answer 2

Gastrulation begins with the formation of the primitive streak at the beginning of week 3

Question 3

Primitive Streak

Answer 3

• epiblasts proliferate and migrate medially
• Elongates cranially
• epiblasts invaginate to form primitive node (at cranial portion of streak) and primitive groove

Question 4

What is the significance of the primitive streak

Answer 4

• determines cranial-caudal axis of embryo
• formation of mesenchyme (embryonic mesoderm)

Question 5

mesenchyme

Answer 5

same thing as embryonic mesoderm; formed by migration of epiblasts from primitive streak (groove) to become embryonic mesoderm

Question 6

formation of embryonic endoderm during gastrulation

Answer 6

migrating cells of primitive streak will also push hypoblasts out of the way to form embryonic endoderm

Question 7

When does primitive streak degenerate

Answer 7

Primitive streak degenerates by the end of week 4; cells of epiblast (through process of gastrulation) give rise to all 3 germ layers of embryo