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
