Pre-embryonic Period

Question 0

What are the main events in the first two weeks of development?

Answer 0

Cleavage and formation of the morula
Compaction and formation of the blastocyst
Implantation begins

Question 1

How long are the pre-embryonic, embryonic and post-embryonic periods?

Answer 1

Pre: weeks 1-3
Embryonic: weeks 3-8
Foetal: weeks 9-38

Question 2

Describe the events of fertilisation

Answer 2

Oocyte released from the ovary
Travels along the Fallopian tube
Fertilised by sperm in the ampulla to form a zygote

Question 3

Where is the idea site for implantation?

Answer 3

Posterior uterine wall

Question 4

How long is an oocyte and a sperm viable for?

Answer 4

Oocyte: 1 day
Sperm: 3 days

Question 5

When does cleavage begin and what does it result in?

Answer 5

30 hours tater fertilisation

2 blastomeres which make up the morula

Question 6

In the morula, what is the differentiation status of the cells?

Answer 6

Totipotent

Question 7

During IVF, when is the morula transferred into the uterus?

Answer 7

After it has divided to the 4 or 8 cell stage

Question 8

What is PGD?

Answer 8

Pre-implantation genetic diagnosis
When a cell is removed from the morula and tested for serious heritable conditions prior to transfer of the embryo to the mothers
Done in IVF

Question 10

What does compaction produce?

Answer 10

A blastocyst

Question 11

Structure of a blastocyst?

Answer 11

Blastocyst cavity
Inner cell mass (embryoblast)
Outer cell mass (trophoblast)
Surrounded by the zona pellucida

Question 12

What is the differentiation status of the cells in the blastocyst?

Answer 12

Pluripotent

Question 13

What happens in hatching?

Answer 13

The blastocyst hatches from the zona pellucida so that it is no longer constrained and free to enlarge

Question 14

What does hatching allow?

Answer 14

The blastocyst is free to enlarge

Can now interact with the uterine surface to implant

Question 15

How many cells are there at the beginning of implantation? How many are for which functions?

Answer 15

107 cells
8 to make the embryo
99 to begin development of the fetal membranes

Question 16

What happens to the outer cell mass in week 2?

Answer 16

Forms two distinct cellular layers

• syncytiotrophoblast
• cytotrophoblast

Question 17

What happens to the inner cell mass in week 2?

Answer 17

Becomes the bilaminar disc

• epiblast
• hypoblast

Question 18

List some conditions linked to implantation defects

Answer 18

IUGR
Pre-eclampsia
Ectopic pregnancy
Placenta praevia

Question 19

What is an ectopic pregnancy?

Answer 19

When there is implantation at a site other than the uterine body

Question 20

What is placenta praevia?

Answer 20

When there is implantation in the lower uterine segment

Question 21

What can placenta praevia lead to?

Answer 21

Haemorrhage in pregnancy

Requires C-section delivery

Question 22

What is the primitive yolk sac produced from?

Answer 22

The blastocyst cavity

Question 23

What happens during implantation?

Answer 23

Syncytiotrophoblast cells invade the epithelium and underlying endometrial stroma with the help of proteolytic enzymes.

Question 24

What are the effects of implantation?

Answer 24

Establishes maternal blood flow within the placenta

Establishes basic structural unir of materno-fetal exchange

Question 25

How does the secondary yolk sac form?

Answer 25

Pinches off from the primitive yolk sac

Question 26

What is the blastocoele?

Answer 26

The first cavity formed as a result of compaction

Question 27

What is the amniotic sac formed from?

Answer 27

Spaces within the epiblast

Question 28

What is the primitive yolk sac formed from?

Answer 28

The hypoblast lining the blastocoele

Question 29

What is the chorionic cavity/extra embryonic coelom formed from?

Answer 29

Spaces within the extraembryonic reticulum and mesoderm