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WEEK 2 SEM 4 > Fertilisation and the Luteal Phase > Flashcards

Fertilisation and the Luteal Phase Flashcards

1
Q

Why is the semen coagulated?

A

to avoid loss of sperm

if not coagulated, sperm would drip down to vagina and not enter cervix

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2
Q

Can freshly ejaculated sperm fertilise an egg?

A

no

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3
Q

How is the semen liquified?

A

similar cascade thrombolysis

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4
Q

What is the difference in the cervical mucus in the follicular phase and the luteal phase?

A

Follicular phase-liquid mucus bc glycoproteins are aligned- sperm easily come in
Luteal phase-mucus is viscous- forms plug- not allow sperm in

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5
Q

What are cervical crypts?

A

grooves on side of cervix
acts as reservoir for sperm
they swim in circles lol

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6
Q

Within how many days does fertilisation occur?

A

1-2 days

5 days sperm can survive in the female reproductive tract

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7
Q

How does the sperm swim to the egg?

A

uterus/uterine tube contractions
cilia
chemo-attractants released from cumulus cells

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8
Q

How does the sperm get hyperactivated as it approaches the egg?

A

tail beating= increased frequency and increased amplitude

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9
Q

What kind of channels do sperms have?

A

Ca2+ channel involved in hyperactivation of sperm (catsper channels)

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10
Q

How many hours after ejaculation are the sperm fertile?

A

4 hours to 18 hours

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11
Q

What makes the sperm fertile?

A

capacitation

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12
Q

Why does capacitation occur?

A

so the role of acrosome doesn’t take place early

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13
Q

What is capacitation?

A

sperm is removed from seminal fluid (by cervical mucus)
surface glycoprotein rearrangement
membrane composition change
Ca2+ channels change

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14
Q

What is the acrosome reaction?

A

when sperm comes into contact with egg

acrosome bursts and enzymes break down zona pelucida

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15
Q

What enzymes are involved with the acrosome reaction?

A

Hyaluronidase- dissolves through Zona Pelucida

Acrosin- bound to inner acrosomal membrane digests Zona Pelucida

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16
Q

What signals the ovary to begin ovulation?

A

LH surge

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17
Q

After ovulation, what does the oocyte complete?

A

meiosis I

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18
Q

What does the oocyte extrude after completing meiosis I?

A

polar body

19
Q

What is a polar body?

A

doesn’t have any cytoplasm and cellular machinary
the division is asymmetrical
the only thing in the polar body is the genetic material as a result of DNA replication during meiosis

20
Q

What happens to the follicle as a result of LH surge?

A

inflammatory response- so turns red
breaks
as the follicle breaks there is tissue remodelling, protease release, GF release

21
Q

How is the corpus luteum formed?

A

mixing of granulosa and theca cells

22
Q

In the first part of the cycle, under Oestrogen influence, what happens to the Endometrium?

A

Proliferation of endometrium= thickens the endometrium

23
Q

What happens in the differentiation of the endometrium?

A

more blood supply
more secretory gland expression
more nutrient secretion
it makes endometrium surface receptive (READY FOR INPLANT)

24
Q

What does progesterone do to cilia?

A

suppresses the beating
bc late in the cycle, the oocyte has already been fertilised
so no more egg/sperm needs to come to the tube

25
Q

What is the lifespan of the corpus luteum if fertilization doesn’t occur?

A

14 days because of the lack of LH (bc progesterone is causing negative feedback)

26
Q

When the corpus luteum dies, what happens?

A

the endometrium will decline and get lost as well leading to menses
due to this, the negative feedback (by progesterone) on the HP axis will also get lifted, and there will be a rise in FSH levels leading to a new cycle

27
Q

How does the corpus luteum die?

A

cell death
vasculature breaks down
corpus luteum shrinks
overtime becomes corpus albicans (whit scars on the ovary)

28
Q

What is hCG similar to?

A

LH
have same alpha subunit but diff beta subunit
in preggo tests look for beta subunit of hCG

29
Q

What is the corona radiata?

A

cells close to egg
active communication with egg
densely packed granulosa cells

30
Q

What are the cumulus oophorus cells?

A

outside corona radiata
granulosa cells
loosely packed
secrete mucus

31
Q

What is Zona Pelucida?

A

glycoprotein

32
Q

What is the perivitelline space?

A

inside zona pelucida- little spaces
this space undergoes changes at fertilisation and this helps block more than one sperm entering into the egg. It prevents polyspermy.

33
Q

What does the sperm bind to on zona pelucida?

A

receptor adhesion molecules (ZP3)

interaction between sperm and zona pelucida is SPECIES SPECIFIC

34
Q

When the egg and sperm touch, how do they become one?

A

through phagocytosis

35
Q

What happens to the sperm tail?

A

it is destroyed

if it enters the egg, it is destroyed

36
Q

What is released from the sperm membrane?

A

Phospholipase Z

37
Q

How does PLZ act?

A
  1. sperm gets into egg
  2. PLZ acts on PIP2 in egg membrane
  3. intracellular Ca2+ from ER in egg
  4. Sign of fertilization
  5. causes cortical reaction to begin
38
Q

What is the cortical reaction?

A 
cortical granules under membrane of egg
this wave causes the release of 
1. proteases
2. peroxides
3. hyaline
39
Q

What do proteases do?

A

the proteases dissolve all the adhesion molecules (ZP3 binding proteins) on the surface of the egg so no more sperm can bind

40
Q

What does peroxides do?

A

peroxides cause crosslinking of the proteins in the zona pellucida making it hard and impermeable-this prevents more than one sperm penetrating the egg (polyspermy)

41
Q

The Ca2+ released in the egg causes what?

A

triggers the egg to complete meiosis II

42
Q

What are the catsper channels?

A 
VG channels
set by pH
as sperm gets closer to egg, environment gets more alkaline= this opens catsper channels
Ca2+ comes in
sperm gets hyperactivated
43
Q

Explain the whole process of syngamy:

A
  1. After meiosis I the oocyte is haploid (23 chromosomes) but each chromosome is bound to its identical sister chromatid.
  2. At fertilisation the sperm binds to the ZP, penetrates it and fuses with the oocyte plasma membrane. This causes the increase in Ca2+ via PLC-zeta that then triggers the cortical reaction and also the completion of meiosis II and the expulsion of the second polar body. So the oocyte is now truly haploid.
  3. The sperm nuclear membrane breaks down and the chromatin decondenses and the chromosomes separate (remember sperm is also haploid)
  4. 4-7 hours after fusion of sperm and egg, the two sets of haploid chromosomes become surrounded by distinct membranes forming pronuclei. Each haploid pronuclei starts to synthesise/replicate its DNA in preparation for the first mitotic division
  5. Then the two pronuclei fuse and the chromosomes become aligned on the mitotic metaphase spindle, the chromosomes move to their appropriate positions down the equator. So that each daughter cell will receive the chromosomes with their homologous pairs (i.e. so each has full 46, diploid number, 23 from dad, 23 from mum).
  6. Mitosis is then complete and the one cell zygote has become a two cell embryo

WEEK 2 SEM 4 (6 decks)

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