Week 3

Question 1

Week 3 is characterized by what main process?

Answer 1

Gastrulation:

Cell migration leading to Trilaminar Germ Disc formation;

Ectoderm

Mesoderm

Endoderm

Question 2

What appears along the midling of the Epiblast surface on day 15?

What are the (3) main constituents?

Answer 2

The Primitive Groove:

1. Primitive Groove
2. Primitive Pit
3. Primitive Node

Question 3

What is the Primitive Pit?

What about the Primitive Node?

Answer 3

1. The Primitive pit is a depression marking the future cranial end of the primitive groove
2. The Primitive Node is the raised epiblast tissue surrounding the Primitive Groove & Pit

Question 4

The first migration of Epiblast cells through the primitive streak initially replaces what cells?

What does this first migration give rise to?

Answer 4

The first migration of Epiblast cells (Day 16) through the primitive streak, initially replaces the underlying Hypoblast, giving rise to the Definitive Endoderm

Question 5

Following the formation of the Endoderm, the second migration of Epiblast cell move where and give rise to what germ layer?

Answer 5

During the 2nd Epiblast migration, the cells diverge into the space between the Epiblast & Endoderm, giving rise to the Intraembryonic Mesoderm

Question 6

The remaining Epiblast cells then give rise to what Germ layer?

Answer 6

The ectoderm

Question 7

What are the two locations at which the Mesoderm does not divide the Ectoderm and Endoderm?

What are their purposes?

Answer 7

1. Buccopharyngeal Membrane: Degraded in the 4th week to form the Oral Cavity
2. Cloacal Membrane: Degraded in the 7th week to form the openings of the anus & Urogenital tracts