Cell Bio Lecture 14 - Development 3

Question 1

Go over the timeline of early development of an embryo.

Answer 1

Membrane fusion: Day -1
Fertilization complete: Day 0
1st Cleavage (2 cell stage): Day 1
2nd Cleavage (4-cell stage): Day 2
3rd Cleavage (8-cell stage): Day 2.5-3
Morula (compaction): Day 3-4
Blastocyst (implantation): Day 4-14
Gastrula: Day 15-17

Question 2

Up to what cellular stage does an embryo have identical, totipotent cells?

Answer 2

Until the 8-cell blastomere stage

Question 3

Up to what cell stage are embryo cell divisions synchronous?

Answer 3

Up to the 8-cell stage

Question 4

What is compaction? (of an embryo)

Answer 4

When the zona pellucida prevents outward growth of the embryo up to the 8-cell morula stage.

Question 5

What is a morula?

Answer 5

The 8-cell embryo

Question 6

Which cell mass eventually forms the embryo?

Answer 6

The inner cell mass (ICM)

Question 7

What does the trophoblast eventually form?

Answer 7

The placenta and most extra-embryonic tissues.

Question 8

At what point are cells removed for PGD?

Answer 8

1-2 blastomeres are removed at the 8 cell stage

Question 9

On what day (after fertilization is complete) does the morula arrive in the uterus?

Answer 9

Day 4-5

Question 10

Further cleavage of the morula results in what?

Answer 10

Formation of a blastocyst.

Question 11

When is the zona pellucida shed?

Answer 11

After early formation of the blastocyst

Question 12

What are two important functions of the zona pellucida following fertilization?

Answer 12

Prevention of size growth and prevention of ectopic pregnancy

Question 13

What is a blastocoel?

Answer 13

The fluid-filled cavity of the blastocyst

Question 14

What confers immunity to the embryo?

Answer 14

PGE2

Question 15

On what day does implantation occur?

Answer 15

~Day 6

Question 16

What two layers make up the bilaminar disc? Which layer will go on to form the germ layers?

Answer 16

Epiblast and hypoblast make up the disc. Epiblast goes on to form the germ layers

Question 17

After the hypoblast delaminates, which germ layer forms in its place?

Answer 17

The endoderm

Question 18

What is the overall early SAB rate?

Answer 18

~50%

Question 19

What are the three major causes of SABs?

Answer 19

1. Chromosomal abnormalities
2. Cleavage problems
3. Progesterone insufficiency

Question 20

Do early SABs contribute to the low overall birth malformation rate? What is that rate?

Answer 20

Yes, the rate is 2-3%