Pre-Embryonic Phase Flashcards
Define ‘pre-embryonic’ phase of human development:
Period 0-2 weeks after fertilisation, until implantation
Name the tubes which connect the ovaries to the uterus:
Fallopian tubes
Name the point in a Fallopian tube where fertilisation usually takes place:
Ampulla of Fallopian tube
Where is the ideal site for implantation?
Posterior uterine wall
Define zygote:
Fertilised oocyte
Define cleavage:
1st division of zygote into 2x blastomeres
Define zona pellucida:
Glycoprotein shell which surrounds the zygote before implantation, preventing polyspermy
Define morula:
Solid ball of blastomeres (totipotent), distinct from blastocyst due to lack of cavity
Define ovary:
Female reproductive organ which produces and releases oocytes
Define uterus:
Female reproductive organ where implantation of the zygote and growth of the embryo/foetus occurs
Name the process in which a morula becomes a blastocyst. What are the differences?
Compaction
- Blastocyst contains a cavity
- Blastocyst contains 2 differentiated cell types (embryoblast and trophoblast), morula = totipotent
Name the 2 cell types found in a blastocyst, and their future derivatives:
1) Trophoblast cells = form supportive structures for embryo
2) Embryonic cells = form embryo
On what day after fertilisation does compaction occur?
Day 4
On what day after fertilisation does the 1st differentiation occur? What name is given to this event?
Day 4
Compaction
On what day after fertilisation does ‘hatching’ occur?
Day 5
Describe ‘hatching’:
Blastocyst ‘hatches’ from zona pellucida
= free to enlarge
= free to interact with uterine wall (implantation)
On what day after fertilisation does implantation begin?
Day 6/7
When implantation begins, how many cells does the conceptus have? How many will form the embryo vs supportive structures?
107 cells
8 will form embryo
99 will form supportive structures
Name 2 implantation defects:
1) Ectopic pregnancy
2) Placenta praevia
Define ectopic pregnancy:
Implantation at a site other than the uterine body
Where do ectopic pregnancies usually occur?
Fallopian tube
Define placenta praevia:
Implantation in lower uterine segment, such that the placenta grows across the cervix
Why would a mother with placenta praevia require a C-section?
To avoid massive haemorrhage
Define blastocyst:
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
Define trophoblast:
Pluripotent cell type found in blastocyst (outer cell mass), which will form supportive structures
Define embryoblast:
Pluripotent cell type found in the blastocyst (inner cell mass), which will form the embryo
Define implantation:
The attachment and invasion of the ‘hatched’ blastocyst to the wall of the uterus, at day 6/7 after fertilisation.
Define cytotrophoblast:
Placental membrane around the yolk sac, derived from the trophoblast
Define syncytiotrophoblast:
Cells that invade maternal sinusoids to create uteroplacental circulation. Derived from trophoblast.
On what day after fertilisation is the bilaminar disc formed?
Day 9
Name the 2 cell types of the bilaminar disc:
1) Epiblast
2) Hypoblast
Once the blastocyst cavity becomes surrounded by hypoblast cells, what is it called?
Primary yolk sac
What 2 cell types does the inner cell mass differentiate into? Together what do they form?
1) Epiblast
2) Hypoblast
Bilaminar disc
What is the name of the cavity surrounded by epiblast cells?
Amniotic cavity
Name the cells that invade maternal sinusoids to create uteroplacental circulation:
Syncytiotrophoblast cells
At what point after fertilisation may bleeding occur, which is often mistaken for menstruation?
End of week 2 ~ day 14
