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Repro > Fertilisation > Flashcards

Fertilisation Flashcards

1
Q

what is coagulated?

A

ejaculated sperm

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2
Q

why is ejaculated sperm coagulated?

A

to prevent loss, later liquifies

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3
Q

what happens to the coagulated sperm?

A

it’s jelly-like, takes about 15 mins to liquify and the sperm swim out

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4
Q

importance of sperm moving through cervical mucus?

A

removes seminal fluid, abnormally morphological sperm and cellular debris

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5
Q

effect of progesterone on cervical mucus?

A

cervical mucus is less viscous in the absence of progesterone allowing sperm to pass

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6
Q

what do cervical crypts do?

A

-ridges on the side of the cervix
that trap sperm which then swim round and round in the ridges and come out at different times
-increases the window of time that the sperm has to meet the egg – increases the chance of them being around when the egg is released

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7
Q

when does fertilisation occur?

A

typically within 24-48 hours

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8
Q

give a suggestion as to how the sperm finds and travels to the oocyte cumulus complex?

A

-chemo-attractants (pH and other factors) released from the oocyte cumulus complex may attract the sperm

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9
Q

what are CatSper channels?

A

VGCC’s on the surface of the sperm which open in response to pH and other factors released from the egg

  • sperm become hyperactivated
  • forceful tail beats with increased frequency and amplitude mediated by Ca2+ influx via CatSper channels.
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10
Q

what does hyperactivity mean?

A

means that means as the sperm gets near the egg it swims much faster

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11
Q

where do the sperm and egg meet?

A

the ampulla (wide portion of the uterine tube, close to the fimbrial end)

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12
Q

where does the embryo spend the first 5-6 days of its life?

A

uterine tube

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13
Q

what is capacitation and how is it achieved?

A
  • biochemical rearrangement of the surface glycoprotein and changes in membrane composition
  • partly achieved by removing sperm from seminal fluid
  • uterine/tubal fluid may contain factors which promote capacitation
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14
Q

why is capacitation needed?

A

prepares the sperm to be able to undergo the acrosome reaction

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15
Q

how long does capacitation take?

A

4-18 hours

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16
Q

does every sperm undergo capacitation for the same length of time - what is the importance of this?

A

each sperm has a slightly different time to capacitate

-widening the window of time that capacitated sperm might meet the egg

17
Q

when does the sperm undergo the acrosome reaction?

A

when sperm comes into contact with zona cumulus complex, binds to ZP3 receptor

18
Q

what is the acrosome?

A

invagination of the sperm membrane to make a fluid-filled compartment that contains enzymes to digest though cells surrounding the egg

19
Q

what happens in the acrosome reaction

A

the acrosomal membrane on the sperm head fuses releasing enzymes that cut through the complex

20
Q

what breaks in ovulation?

A

basement membrane, blood pours into the middle

21
Q

what mix in ovulation?

A

theca and granulosa become mixed

22
Q

another name for the follicular phase (of the ovary)?

A

proliferative phase (of the uterus)

23
Q

another name for the luteal phase (of the ovary)?

A

secretory phase (of the uterus)

24
Q

what happens in the follicular/proliferative phase?

A
  • dominated by oestrogen, levels go up causing endometrium proliferation
  • LH surge, meiosis 1 completion, ovulation
25
Q

what happens in the luteal/secretory phase?

A

dominated by progesterone, which:

  • makes the endometrium secretory and receptive to implantation
  • supresses cilia in uterine tubes once oocyte has already passed.
  • makes cervical mucus viscous again to prevent further sperm penetration

also some oestrogen secreted from CL, which helps maintain endometrium in luteal phase

26
Q

role of oestrogen in follicular vs luteal phase

A

follicular is proliferation of endometrium, luteal is maintenance of endometrium

27
Q

why would the CL need beta-HCG to survive?

A

because otherwise its essentially killing itself

  • it is producing progesterone, which will negatively feedback on the HPG axis, decreasing LH levels
  • less LH is able to bind to CL, so CL would die
  • hence beta-HCG from embryo binds to LH receptors on the CL to maintain its survival
28
Q

what happens as a consequence of the CL dying?

A

endometrium sheds, menstruation

-because CL stops making progesterone, which is needed to maintain the endometrium

29
Q

what is the zona pellucida?

A

secreted by the egg, impenetrable after the cortical reaction (inner layer)

30
Q

what is the Cumulus oophorus?

A

derived from granulosa cells, protects the egg (very outside layer)

31
Q

what is the corona radiata?

A

the innermost layer of cumula cells, in contact with the ZP

-formed by granulosa cells adhering to the oocyte before it leaves the ovarian follicle (middle layer)

32
Q

explain sperm binding and penetration?

A
  • sperm comes into contact with the zona-cumulus complex, penetrates cumulus and comes into contact with ZP via ZP3 receptor
  • enzymes digest through ZP, sperm fuses with plasma membrane and taken in by phagocytosis
  • phospholipase Zeta activated by basal Ca2+ inside egg
  • PIP2 → DAG + IP3
  • release of intracellular Ca2+, large Ca2+ spike
  • cortical reaction as wave of Ca2+ sweeps around egg
  • release of proteases, peroxides and hyaline prevents polyspermy
33
Q

ca2+ release causes what?

A

completion of meiosis II, expelling of the second polar body and the cortical reaction

34
Q

explain what syngamy is and what happens

A

it is the fusion of 2 nuclei

  • sperm nuclear membrane breaks down, the chromatin decondenses and chromosomes separate
  • 4-7 hours after sperm penetration the two sets of haploid chromosomes (male and female) become surrounded by distinct membranes forming two pronuclei
  • pronuclei synthesise DNA in preparation for the first mitotic division
  • pronuclei fuse, spindle forms and chromosomes line up
  • completion of mitosis
  • one cell zygote becomes a two cell embryo

Repro (11 decks)

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