ToB Embryology 1 - Pre-Embryonic Period Flashcards
How early in development does the first differentiation take place?
Within the first 2 weeks
What is the first differentiation that occurs?
- Intra-embryonic tissues
- Extra-embryonic tissues
What is meant by ‘intra-embryonic tissues’?
Tissues that will become part of the body
What is meant by ‘extra-embryonic tissues’?
Tissues which will not become part of the body, but will support the development of the body
Why is there a difference between the length of complete gestation, and the length of pregnancy term?
Complete gestation is 38 weeks, but pregnancy weeks are calculated from the last menstrual period, ie conception weeks + ~2 weeks = 40 weeks
How long is the pre-embryonic period?
2 weeks
What are the 3 main stages from fertilisation to birth?
1) Pre-embryonic
2) Embryonic
3) Fetal
What is the name of the first division after fertilisation, and what does it produce?
‘Cleavage’ to produce 2 blastomeres
What is the name of the group of cells which makes contact with the endometrial lining of the uterus?
Blastocyst
At what point of the fallopian tube is the oocyte fertilised?
At the ampulla (end nearest the ovary)
What is the name of a fertilised oocyte?
Zygote
Where is the ideal site for implantation?
Posterior uterine wall, within the endometrial lining of the uterus
How long is an oocyte viable for?
1 day
How long is a sperm viable for?
3 days
How soon does cleavage occur after fertilisation?
About 30hrs
Why are the 2 blastomeres (created via cleavage) the same size as the oocyte?
The cells cannot expand as they are encased by the zona pellucida (glycoprotein shell)
Define zona pellucida:
Thick glycoprotein membrane surrounding the ovum before implantation, which prevents polyspermy
How are other sperm prevented from reaching the oocyte after it has been fertilised?
They are excluded by the zona pellucida
Define morula:
Group of totipotent blastomere cells, formed after cleavage and compaction, distinct from a blastocyst due to lack of cavity.
Why are the cells within the morula described as totipotent?
As the cells are identical at this point, they all have the capacity to become any cell point.
During IVF, what is the name of the group of cells which will be transferred into the uterus?
Morula
When can Pre-implantation Genetic Diagnosis occur?
During the morula stage of IVF, before cells are transferred into the mother
What process allows embryos to be screened for serious heritable conditions?
Pre-implantation Genetic Diagnosis (PGD), during IVF
Define the embryonic period of development:
Period 3-8 weeks after fertilisation, during which all the structures and systems are built
Define the fetal period of growth:
Period 9-38 weeks after fertilisation, during which growth is the focus (as all structures and systems have been built). Physiological maturation of the systems occurs.
Define the pre-embryonic period:
Period 0-2 weeks after fertilisation, during which cleavage and the 1st differentiation takes place, and implantation begins.
Define zygote:
A fertilised oocyte
Describe cleavage:
The 1st division of the zygote, into two masses known as blastomeres. First cleavage happens ~30 hours after fertilisation
Define ovary:
The female reproductive organ producing oocytes/eggs for fertilisation
Define fallopian tube:
Either of a pair of tubes along which oocytes/eggs travel along from the ovaries to the uterus
Define uterus:
Female reproductive organ where implantation of the zygote and growth of the embryo occurs
Define gestation:
The carrying of an embryo/fetus inside a female reproductive organ.