12. Embryology Flashcards
What stage is the primary oocyte arrested in until puberty?
Prophase 1 of meiosis 1
When does the primary oocyte complete meiosis 1?
Puberty - secondary oocyte is released every month
What is produced from oogenesis?
1 ovum
3 polar bodies
What is produced from spermatogenesis?
4 spermatozoa
Where does fertilisation usually take place?
Ampullary region of fallopian tube
What happens in ovulation?
Secondary oocyte is released from the ovary and swept into the fallopian tube by the frimbriae.
How long are sperm viable for?
5 days
How long is a secondary oocyte viable for?
12-24 hours
What changes occur to sperm in order to enable fertilisation?
- Capacitation
2. Acrosome reaction
What is capacitation?
When the sperm comes into contact with vaginal secretions, they undergo changes to their cell membane and become hypermobile to allow fertilisation.
What is the acrosome reaction and when does it occur?
When sperm binds to the zona pellucida, it releases enzymes that break down the glycoprotein and allow penetration of the egg.
Once a sperm enters the egg, what structural change occurs?
Zona pellucida hardens to prevent any other sperm from entering.
What process occurs within the oocyte once it has been fertilised?
Meiosis II is completed to form a female pronucleus which fuses with the male pronucleus to form a zygote.
Outline the structures which surround the secondary oocyte.
Surrounded by:
Zona pellucida - glycoprotein
Zona radiata
Outline what happens after zygote formation in order to produce a blastocyst.
Cell division to eventually form a 16-cell morula which comprises of an inner cell mass and an outer cell mass.
Outline how a morula develops into a blastocyst.
Inner cell mass becomes the embryoblast.
Outer cell mass becomes the trophoblast.
Cavity is formed beneath the embryo blast.
Zone pellucida degenerates “hatching”.
When does implantation take place?
Day 6
What happens during implantation?
Blastocyst is implanted into endometrium wall
What is the function of the zona pellucid, why does “hatching” take place?
Zone pellucida prevents the morula/blastocyst adhering to the fallopian tube.
ZP stops the morula enlarging so degenerates to allow blastocyst formation.
What is the most common location for implantation to happen?
Upper past of uterus body, in the posterior wall.
Outline what happens to the blastocyst in week 2, following implantation.
- Trophoblast differentiates into 2 layers
- Embryoblast differentiated into 2 layers
- 2 cavities are formed
What 2 layers does the trophoblast differentiated into?
Inner - cytotrophoblast
Outer- synctiotrophoblast
What 2 layers does the embryoblast differentiated into?
Epiblast
Hypoblast
What 2 cavities are formed during week 2?
Yolk sac
Chorionic cavity
What is placenta previa, what are the implications of this?
Placenta develops unusually low, covering the cervix. Cesarean section is necessary.
What is histiotrophic nutrition and when is it most important?
Nutrition provided to the embryo which is not from the maternal blood.
Important up to 12th week.
What is haemotrophic nutrition and when is it important?
Nutrition provided from the mothers blood, important 12th week onwards.
What is the embryonic age?
Time since fertilisation
What is the gestational age?
Time since last menstruation (embryonic age + 2 weeks usually)
When is the embryonic period?
Weeks 3-8
When is the foetal period?
Week 9 - birth at 38 weeks embryonic age/ 40 weeks gestational age.
