Embryology Weeks 1-3

Question 1

What is a morula

Answer 1

Early stage embryo consisting of 16 in a solid ball contained in the zona pellucida. It usually occurs 72 hours after fertilisation

Question 2

What is the zona pellucida

Answer 2

A thick, gelly, protective coat

Question 3

Describe the transition of morula to blastocyst stage.

Answer 3

Morula travels down fallopian tube, into uterine cavity and implants into endometrium. Fluid beings to accumulate in intracellular spaces which merge into a blastocyst cavity. At this stage the embryo is called a blastocyst.

Question 4

What occurs on Day 8 to the blastocyst.

Answer 4

Inner cell mass diferentiates into epiblast and hypoblast, forming a bilaminar disc. Amniotic cavity forms within epiblast

Question 5

Describe how the endoderm and mesoderm forms

Answer 5

Endoderm forms when epiblast cells from the primitive streak migrate and replace hypoblast cells.
Mesoderm forms when epiblast cells spread between the two layers

Question 6

Describe the formation of the notochord

Answer 6

Embryo has prenotochordal cells that migrate through primitive streak to form the notochordal plate within endoderm. The notochordal plate then detaches from the endoderm and forms the notochord which is established in the head region first.

Question 7

What is the function of the notochord?

Answer 7

It activates a signalling pathway involve in tissue differentiation and development.

Question 8

What does the mesoderm divide into?

Answer 8

Paraxial mesoderm, intermediate mesoderm and lateral plate mesoderm.

Question 9

What will the paraxial mesoderm differentiate into?

Answer 9

Somites (sclerotome, myotomes and dermatomes) and head mesenchyme

Question 10

What will intermediate mesoderm develop into?

Answer 10

Urogenital system

Question 11

What will the lateral plate mesoderm develop into?

Answer 11

Walls of body cavities, serous membranes and circulatory system