Lecture 14: The trilaminar embryo

Question 1

Gastrulation

Answer 1

The formation of the three germ layers, ectoderm, mesoderm, endoderm through formation of trilaminar germ disk

Question 2

Primitive Groove

Answer 2

At the beginning of gastrulation, cells proliferate at the caudal end of the bilaminar plate’s midline, forming a groove with elevations on either side.

Question 3

Primitive Pit

Answer 3

At the caudal end of the primitive groove, epiblast cells migrate inwards towards hypoblasts

Question 4

Primitive node

Answer 4

Dense concentration of cells surrounding the primitive pit

Question 5

Primitive streak

Answer 5

primitive groove, pit and node all together. gives bi-lateral symmetry and cranial-caudal axis to embryo. Elongates cranially

Question 6

Embryonic ectoderm

Answer 6

develops from non-migrating epiblasts

Question 7

Embryonic endoderm

Answer 7

develops from migrating epiblasts, which replace hypoblasts

Question 8

Embryonic mesoderm

Answer 8

develops from migrating epiblasts that become sandwiched between ectoderm and endoderm; also called mesenchyme

Question 9

Regions there is no mesoderm

Answer 9

Buccopharyngeal area (site of future mouth)
Cloacal area (site of distal openings of the digestive and urogenital tracts)