Pre-Embryonic Phase

Question 1

Define ‘pre-embryonic’ phase of human development:

Answer 1

Period 0-2 weeks after fertilisation, until implantation

Question 2

Name the tubes which connect the ovaries to the uterus:

Answer 2

Fallopian tubes

Question 3

Name the point in a Fallopian tube where fertilisation usually takes place:

Answer 3

Ampulla of Fallopian tube

Question 4

Where is the ideal site for implantation?

Answer 4

Posterior uterine wall

Question 5

Define zygote:

Answer 5

Fertilised oocyte

Question 6

Define cleavage:

Answer 6

1st division of zygote into 2x blastomeres

Question 7

Define zona pellucida:

Answer 7

Glycoprotein shell which surrounds the zygote before implantation, preventing polyspermy

Question 8

Define morula:

Answer 8

Solid ball of blastomeres (totipotent), distinct from blastocyst due to lack of cavity

Question 9

Define ovary:

Answer 9

Female reproductive organ which produces and releases oocytes

Question 10

Define uterus:

Answer 10

Female reproductive organ where implantation of the zygote and growth of the embryo/foetus occurs

Question 11

Name the process in which a morula becomes a blastocyst. What are the differences?

Answer 11

Compaction

• Blastocyst contains a cavity
• Blastocyst contains 2 differentiated cell types (embryoblast and trophoblast), morula = totipotent

Question 12

Name the 2 cell types found in a blastocyst, and their future derivatives:

Answer 12

1) Trophoblast cells = form supportive structures for embryo

2) Embryonic cells = form embryo

Question 13

On what day after fertilisation does compaction occur?

Answer 13

Day 4

Question 14

On what day after fertilisation does the 1st differentiation occur? What name is given to this event?

Answer 14

Day 4

Compaction

Question 15

On what day after fertilisation does ‘hatching’ occur?

Answer 15

Day 5

Question 16

Describe ‘hatching’:

Answer 16

Blastocyst ‘hatches’ from zona pellucida
= free to enlarge
= free to interact with uterine wall (implantation)

Question 17

On what day after fertilisation does implantation begin?

Answer 17

Day 6/7

Question 18

When implantation begins, how many cells does the conceptus have? How many will form the embryo vs supportive structures?

Answer 18

107 cells
8 will form embryo
99 will form supportive structures

Question 19

Name 2 implantation defects:

Answer 19

1) Ectopic pregnancy

2) Placenta praevia

Question 20

Define ectopic pregnancy:

Answer 20

Implantation at a site other than the uterine body

Question 21

Where do ectopic pregnancies usually occur?

Answer 21

Fallopian tube

Question 22

Define placenta praevia:

Answer 22

Implantation in lower uterine segment, such that the placenta grows across the cervix

Question 23

Why would a mother with placenta praevia require a C-section?

Answer 23

To avoid massive haemorrhage

Question 24

Define blastocyst:

Answer 24

Post-morula stage, after 1st differentiation so contains pluripotent cell types + cavity, surrounded by zona pellucida:

• Inner cell mass = embryoblast cells
• Outer cell mass = trophoblast cells

Question 25

Define trophoblast:

Answer 25

Pluripotent cell type found in blastocyst (outer cell mass), which will form supportive structures

Question 26

Define embryoblast:

Answer 26

Pluripotent cell type found in the blastocyst (inner cell mass), which will form the embryo

Question 27

Define implantation:

Answer 27

The attachment and invasion of the ‘hatched’ blastocyst to the wall of the uterus, at day 6/7 after fertilisation.

Question 28

Define cytotrophoblast:

Answer 28

Placental membrane around the yolk sac, derived from the trophoblast

Question 29

Define syncytiotrophoblast:

Answer 29

Cells that invade maternal sinusoids to create uteroplacental circulation. Derived from trophoblast.

Question 30

On what day after fertilisation is the bilaminar disc formed?

Answer 30

Day 9

Question 31

Name the 2 cell types of the bilaminar disc:

Answer 31

1) Epiblast

2) Hypoblast

Question 32

Once the blastocyst cavity becomes surrounded by hypoblast cells, what is it called?

Answer 32

Primary yolk sac

Question 33

What 2 cell types does the inner cell mass differentiate into? Together what do they form?

Answer 33

1) Epiblast
2) Hypoblast
Bilaminar disc

Question 34

What is the name of the cavity surrounded by epiblast cells?

Answer 34

Amniotic cavity

Question 35

Name the cells that invade maternal sinusoids to create uteroplacental circulation:

Answer 35

Syncytiotrophoblast cells

Question 36

At what point after fertilisation may bleeding occur, which is often mistaken for menstruation?

Answer 36

End of week 2 ~ day 14