Lecture 11 - Pre-implantation Development

Question 1

The oocyte is surrounded by a layer called the ______

Answer 1

Zona pellucida

Question 2

Describe the stages between oocyte to blastocyst (5)

Answer 2

Oocyte + sperm

Single cell zygote

2 cell embryo

Morula

Blastocyst

Question 3

What does the zygote become after multiple cell divisions?

Answer 3

Multicellular embryo

Question 4

In the early embryo, cell numbers ____ while mass _____ this is possible as daughter cells become _____

Answer 4

In the early embryo, cell numbers increase while mass stays constant. This is possible as daughter cells become increasingly smaller.

Question 5

What are blastomeres?

Answer 5

Cells formed by cleavage

Question 6

What is compaction?

Answer 6

When cells become tightly packed past the 8-cell stage

Question 7

What is the morula?

Answer 7

Solid ball of 16 blastomeres, surrounded by zona pellucida

Question 8

What is the difference between the inner cell mass and the trophoblast?

Answer 8

The inner cell mass consists of cells on the inside of the morula

The trophoblast consists of cells on the outside of the morula (syncytial or cellular)

Question 9

What is YAP and what does it do?

Answer 9

YAP

Question 10

List the 3 models explaining differentiation of embryonic cells into ICM and trophoblast

Answer 10

1. Mosaic model - no longer accepted
2. Positional model - differentiation depending on if completely surrounded or not / exposure to external environment
3. Polarity model - parallel = both polar and outside, orthogonal = one polar (trophoblast) and the other apolar (ICM)

Question 11

Describe the process of cavitation

Answer 11

Fluid moves through the trophoblast into the centre of the morula and forms a cavity - blastocyst cavity/blastocoele - organism now known as a blastocyst

Question 12

What happens to the ICM when the blastocoele expands?

Answer 12

The ICM is pushed to one end of the fluid filled ball

Question 13

What is the breakdown of the zona pellucida referred to?

Answer 13

Hatching

Question 14

How does the bilaminar embryo arise? What happens at this stage?

Answer 14

ICM becomes divided into two different layers: hypoblast and epiblast

Embryo implants at this stage

Question 15

What does the epiblast become?

Answer 15

All tissues forming part of the human fetus

Question 16

What does the hypoblast together with the epiblast contribute to?

Answer 16

Extra-embryonic support structures

Question 17

Describe the formation of the amniotic cavity

Answer 17

Roof formed by squamous cells which create a membrane known as the amnion - derived from the epiblast

Floor of amniotic cavity formed by epiblast proper

Amniotic cavity filled with amniotic fluid

Question 18

Describe the formation of the yolk sac and its function

Answer 18

Cells derived from the hypoblast begin to migrate and eventually cover the inside surface of the blastocoele, forming a new cavity known as the yolk sac.

Provides blood cells to the embryo and gives rise to the germ line that will migrate into the gonads. Relatively empty in humans and nourishes embryo during 2/3 week of development.