Conception Flashcards
What is conception?
The union of a male sperm and a female secondary oocyte (in metaphase II) forming a zygote.
Where does the zygote implant after division?
In the uterine wall.
Name the six key steps of fertilisation.
Sperm transport, sperm capacitation, acrosomal reaction, polyspermy block, completion of meiosis II, zygote formation.
What happens to semen immediately after ejaculation?
It coagulates into a loose gel to protect sperm and hold it at the cervical os.
How does estrogen affect cervical mucus around ovulation?
It reduces viscosity and changes structure to aid sperm passage.
What assists sperm movement through the uterus?
Pro-ovarian myometrial contractions enhanced by prostaglandins in semen.
How long can sperm survive in the female reproductive tract?
Up to 5 days.
What triggers sperm capacitation?
Uterine secretions.
Name 3 key changes during capacitation.
Cholesterol efflux, glycoprotein redistribution, increase in CatSper channels.
What are the outcomes of capacitation?
Preparation for the acrosomal reaction and hyperactivated motility.
What is the cumulus-oocyte complex (COC)?
The oocyte surrounded by cumulus granulosa cells.
How does sperm penetrate the COC?
Using hyaluronidase to dissolve hyaluronic acid between cells.
What is the zona pellucida composed of?
Glycoproteins: ZP1, ZP2, ZP3, ZP4.
Which ZP glycoprotein binds human sperm?
ZP3.
What triggers the acrosomal reaction?
Sperm binding to ZP3.
What enzymes are released during the acrosomal reaction?
Hydrolytic and proteolytic enzymes to digest the ZP.
What is the cortical reaction?
A Ca²⁺-mediated process that prevents polyspermy after sperm-oocyte fusion.
What is the fast block to polyspermy?
Na⁺ influx causes membrane depolarisation to repel sperm (short-lasting).
What is the slow block to polyspermy?
Ca²⁺-triggered cortical granule release hardens the membrane (long-lasting).
What triggers completion of meiosis II?
Ca²⁺ released during the cortical reaction.
What is produced after meiosis II?
A definitive ovum and a polar body.
What forms the zygote?
Fusion of sperm and ovum pronuclei (2n).
What is a morula?
A 16-cell embryo (day 3–4) with totipotent cells.
When does the embryo become a blastocyst?
At day 5.
What characterises a blastocyst?
Inner cell mass, blastocoele cavity, trophoblasts.
When does implantation occur?
Days 7–8, at the late blastocyst stage.
