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Repro > fertilisation and the luteal phase > Flashcards

fertilisation and the luteal phase Flashcards

1
Q

what happens to sperm during ejaculation

A
  • sperm exits epididymis
  • gets mixed with secretions from seminal vesicles and prostate.
    former coagulates, making semen thick and glopy preventing sperm and semen from seperating.
    latter liquifies the ejaculate
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2
Q

why is it easier for sperm to get to uterus after ovulation of the female

A
  • after ovulation = more bf to the cervix
  • cervical os will be more open and more oedema so cervical mucus is thinner
  • so easier for sperm to get to uterus
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3
Q

when is cervical mucus thin

A

when oestrogen is high around ovulation and this makes it easy for sperm to swim up.

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4
Q

when is cervical mucus thickened

A

6/7 days post-ovulation, progesterone peaks.

cervical mucus thickens to prevent sperm (&pathogens) from entering.

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5
Q

why does cervical mucus thicken after ovulation

A

thickest at 6/7 days post ovulation
bc by 7 days, the blastocyst would have implanted
if oocyte hasn’t been fertilized it is now too late for fertilisation so don’t want sperm entering into the uterus.

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6
Q

why does progesterone rise after ovulation

A

causes cervical mucus to thicken .’. plugged cervical os .’. sperm/pathogens cannot enter.

is also good for implantation; allows formation of receptive differentiated endometrium to accept egg.

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7
Q

what is the cervical crypts

A

infoldings of the endocervix, which act as a reservoir, releasing sperm over several hours and maximising the potential for pregnancy

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8
Q

how long do sperm survive

A

usually reach the oocyte in about 24-48 hours, so survive around this amount of time
However sperm has been found in the female even up to five days after intercourse.

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9
Q

how do sperm navigate to the uterus

A

not well understood.
uterine or tubal cilia may play a role.
chemotaxis may also play a role

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10
Q

how do they sperm change on capitation

A

they become hyperactivated, their tail beats more forcefully with increased frequency and amplitude.
thought to be due to influx of Ca2+ via CatSper channels

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11
Q

what is capitation of sperm

A

functional maturation of spermaozoon = series of changes involving biochemical rearrangement of the surface glycoproteins and changes in membrane composition.

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12
Q

what are CatSper channels

A

volt. gated cation channels. set by pH.

closer to egg = more alkaline environment .’. CatSper channels open .’. influx of Ca2 .’. sperm hyperactivated

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13
Q

how is capitation of sperm achieved

A
  • removing the sperm from seminal fluid (that contains factors inhibiting capacitation)
  • uterine/tubal fluid may contain factors that promote capacitation
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14
Q

when does the acrosome reaction occur

A

when sperm is right next to the egg

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15
Q

what is the acrosome reaction

A

where the acrosome (holding the bag of enzymes) on the sperm head fuses with the egg

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16
Q

what is is significance of acrosome reaction

A

acrosome on sperm head fuses with the egg releasing enzymes that cut through the outer layers of the cumulus that surround the oocyte

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17
Q

what does the acrosome contain

A

bag of enzymes including acrosin

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18
Q

what is acrosin

A

a digestive enzyme that is bound to the inner acrosomal membrane and digests the zona pellucida so the sperm can enter into the oocyte

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19
Q

why do we get LH surge in ovulation

A

sustained high oestrogen at the end of the follicular phase causes switch to positive feedback leading to the LH surge

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20
Q

what does the LG surge mean for the egg

A

The LH surge causes meiosis I to complete, the 1st polar body is extruded and you’re left with the secondary oocyte.

21
Q

what is the luteal phase

A

occurs after ovulation, before pregnancy starts
During this time, the lining of your uterus normally gets thicker to prepare for a possible pregnancy
follicle thickness inceases

22
Q

what is the secretory phase

A

occurs after ovulation, before pregnancy starts
During this time, the lining of your uterus normally gets thicker to prepare for a possible pregnancy
endometrium thickness increases

23
Q

what happens when progesterone reaches its peak (in secretory phase)

A

supresses the cilia and secretions in the uterine tubes

bc the oocyte has already passed -> get rid of cilia bc too late for fertilisation

24
Q

what releases oestrodiol

A

corpus luteum

25
Q

what is the role of oestrodiol

A

lesser role =help maintain the endometrium in the luteal phase
main role = proliferation of the endometrium in follicular phase

26
Q

what is the inbuilt lifespan of the corpus luteum (if no fertisation)

A

14 days

27
Q

what is the significance of the death of corpus luteum

A

This tells the body that fertilisation didn’t occur and an embryo didn’t implant.

28
Q

what happens once the corpus luteum has degenerated

A

stops producing progesterone .’.fall in progesterone = endometrium cannot be maintained .’. this is the start of the next menstrual cycle.
low progesterone = FSH (and LH) rise

29
Q

how do we prevent endometrium shedding when there is a pregnancy

A

embryo throphoblasts release hCH which binds to LH receptors on the corpus luteum + stops it from dying. maintains high progesterone levels
.’. endometrium is kept nice, thick and receptive

30
Q

what is the cumulus oophorous

A

a cluster of cells surround the oocyte both in the ovarian follicle and after ovulation.
used to be granulosa cells
protect the egg and secrete mucus

31
Q

what is the corona radiata

A

Underneath the cumulus cells.
a secretion of extracellular matrix that is made from a couple of layers of granulosa cells
main component of the corona radiata is hyaluronic acid

32
Q

what is the zona pellucida

A

zona pellucida is a glycoprotein layer secreted by the egg first whilst is in follicle

33
Q

what is the purpose of the zona pellucida

A

contains glycoproteins involved in binding sperm

is important in adhering to proteins in sperm head membrane

34
Q

why don’t we get inter species beeding

A

each species sperm binding proteins (on z.pellucida) are specific

35
Q

where is the perivitelline space

A

underneath the z. pellucida

36
Q

what is the role of the perivitelline space

A

space undergoes changes at fertilisation which helps to block more than one sperm entering the egg
- prevents polyspermy

37
Q

how does the egg chame near ovulation

A

Near ovulation the granulosa cells secrete the corona radiata and the granulosa become a loose complex that surrounds the egg.

38
Q

what releases hyaluronidase & what is its purpose

A

released from the acrosome.

digests through cumulus cells and corona radiata

39
Q

what releases acrosin and what is the purpose of this

A

released from the acrosome

digests through the z.pellucida

40
Q

what happens to the sperm on fertilisation

A

sperm membrane fuses with oocyte plasma membrane.
enters cell
nucleus falls into oocyte cytoplasm

41
Q

what happens to electrolytes on fusion of oocyte with sperm

A

When the sperm head fuses with the oocyte plasma membrane and the nucleus falls in it triggers a huge spike in calcium in the egg.

42
Q

why does calcium spike on fertilisation

A

occurs via phospholipase C pathway
in sperm this is called called PLC-zeta.
when sperm enters egg triggers the PIP pathway (=rise Ca2)

43
Q

what is the result of spike in Ca2+ at fertilisation

A 
cortical granules (from under oocyte membrane) release enzymes
mucopolysaccharides released into the perivitilline space.
release of proteases that cleave adhesion molecule that sperm bind to (so only one sperm can bind)
release peroxidase = cross-link formation in the ZP making it hards + prevents polyspermy
44
Q

what does syngamy mean

A

the fusion of two cells or their nuclei in reproduction

45
Q

how do we form an embryo from an egg and sperm

A

1 - after meiosis I, oocyte is haploid (23 chromosomes. each is bound to its sister chromatid)
2 - at fertilisation, sperm->ZP. penetrates, fuses w/ oocyte. increase in Ca2+ -> cortical reaction. Meiosis 2 + expulsion of second polar body. Oocyte =haploid.
3 - sperm nuclear membrane breaks down. chromatin condenses + chromosomes separate
4 - 4-7hr after fusion, 2 sets of haploid chromosomes with distinct membranes around them (= pronuclei)
5- each pronuclei replicate DNA in prep of first mitotic division
6 - pronuclei fuse
7 - chromosomes align on metaphase spindle
mitosis complete. one cell zygote become two cell embryo

46
Q

what happens in syngamy between the egg and sperm

A

1 - sperm enters oocyte. spike in Ca2+ due to PLC-zeta.
2 - cortical reaction (prevent polyspermy)
3 - completion of meiosis II & expulsion of 2nd polar body.
4 - formation of male and female pronuclei (haploid dna each)
5 - both pronuclei replicate their dna
6 - pronuclei fuse alignment of chromosomes down the spindle
7 - mitosisi complete. 2 cells with 46 chromosomes

47
Q

what is the first sign of fertilisation in IVF

A

formation of 2 pronuclei

48
Q

what cells form the placenta in a developing embryo

A

trophoblast

Repro (13 decks)

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