final exam Flashcards
When can the oocyte be fertilised?
Once the oocyte is ovulated it remains viable for 12 to 24 hours and the chance of pregnancy after that drops to almost zero after that.
How much can a sperm survive ?
it usually survives at least 48 hours after the ejaculation
Where does fertilisation occurs ?
Fertilisation occurs in the uterine tube or fallopian tube. Once ovulation has occurred, the secondary oocyte its swept into the fallopian tube by the fimbriae.
what environment has the sperm has to go through ?
it has to survive the acidic environment of the vagina, pass the cervical mucus to reach the uterus. They are propelled by their tail and uterine contractions during intercourse.
What causes cervical contractions ?
oestrogen, prostaglandins and orgasm which help sperms disperse throughout the uterine cavity
What process does the sperm has to overcome before ferilisation?
Capacitation
Capacitation?
It is a biochemical process where acrosomal membrane thins and becomes fragile so the enzymes can be released at the right time to allow penetration.
How do sperms know where to go ?
sperm receptors, respond to chemical stimuli and smell of the ovum.
the mature oocyte secretes..
a chemoattractant called allurin
which layers does the sperm need to penetrate with help of ……….. enzymes.
the protective layers called CORONA RADIATA AND ZONA PELLUCIDA using enzymes within the acrosome.
where are sperm capacitated?
in the uterine tube
which layer has to be penetrated to trigger the acrosomal reaction
The zona pellucida, the sperm head binds to the sperm receptor opening Ca channels which triggers the arosomal reaction.
What do acrosomal enzymes do ?
They digest holes in the zona pellucida.
once the path is cleared out the sperm whips back and forth rocking the sperm head to the oocyte plasma membrane.
what happens when the sperm binds to the oocyte plasma receptors ?
The sperm and the oocyte plasma membrane fuse and the cytoplasmatic contents spill into the oocyte.
What is the cortical reaction?
exocytosis from the cotical granules causes the zona pellucida to harden and sperm- binding receptors are clipped of by ZONL INHIBITORY PROTEINS. Also when the oocyte binds to the sperm it sheds taking all the receptors off
Pronucleus ?
Sperm nucleus and the ovum nucleus then both swell forming male pronucleus and the female pronucleus: two nuclei contained within the same cell membranes.
first phase of fertilisation ?
the paternal and maternal chromosomes from the pronuclei combine and intermix. The now diploid and called a zygote
What is cleavage?
produces fast mitotic division after fertilisation. cells become smaller.
Morula ?
16 cells have formed
4-5 days of ovulation which phase ?
blastocyst forms with the degenerating of the zona pellucida
how does a blastocyst looks like ?
is a single layer hollow ball of about 50 cells encircling a fluid filled cavity with dense ,mass of cells together at one side
What does the inner cell mass and develops into ?
a foetus
What makes the foetal portion of the placenta ?
Trophoblast
after how many days does placentation happens after fertilisation ?
6 days, it implants closer to the cervix, it may later separate
how pregnancy supported ?
What does trophoblast make ?
they make chrorionic gonadotropin peaks around the 8 weeks.
HCG acts like a luteinising hormone
What does HCG stimulates ?
it stimulates the corpus luteum to produce oestrogen and progesterone up until about 8-10 weeks of gestation. AFTER THAT IT IS RESPONSABILITY OF THE PLACENTA
After fertilisation, the zygote goes through a rapid period of cells divisions called
Cleavage
What is the specialised mitotic division does the zygote undergo?
cleavage
What are the levels human chorionic gonadotropin hormone during pregnancy ?
HCG is detectable after one week of fertilisation and they continue to rise until the eight week, after that they begin to decline reaching their lowest level at the fourth month of gestation,
How long is the embryonic period ?
It is the the first 8 weeks after conception during which every major organ system is being developed an
When is the oocyte considerate a zygote ?
When the chromosomes of the pronuclei intermix, Fertilisation is accomplished and now the cell is considerate to by a zygote and its ready to for the first cleavage division.
When does embryonic development begins?
With fertilisation continues with the embryo floats through the uterine tube, into the uterine cavity and implants into the uterine wall.
what are blastomeres ?
the first cleavage of zygotes produces identical cells, only after 36 hours after fertilisation