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RED > L06: Fertilisation > Flashcards

L06: Fertilisation Flashcards

1
Q

What 2 things are required from each other sexes for fertilisation to occur

A

Sperm

Egg

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2
Q

Where does the sperm mature

A

In the male tract- epididymis

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3
Q

What does capacitation of the sperm occur

A

In the female tract

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4
Q

What meiosis is the egg after ovulation arrested at

A

Meiosis 2 metaphase 2

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5
Q

After ovulation of the egg what picks up the egg to carry it in the uterine tube

A

Fimbrae

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6
Q

What allows the egg to become picked up by the fimbrae

A

Follicular fluid in the oocyte that contains chemoattractants

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7
Q

What allows the movement of the egg within the uterine tube

A

Muscle contracts

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8
Q

What happens to the number of sperm as it moves up the female tract

A

Decreases

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9
Q

What happens to the sperm in the upper vagina

A

Coagulates

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10
Q

What cause the sperm to coagulate in the upper vagina

A

Semenogelin

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11
Q

What causes the breakage of semenogelin afterwards to allow the sperm to flow out

A

PSA (prostate specific antigen)

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12
Q

If sperm move up through the vagina where does it next enter

A

The cervix

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13
Q

When is the cervix least viscous

A

During 9-16 days of the cycle

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14
Q

What does the less viscosity of the cervix allow the sperm for

A

Sperm selection

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15
Q

What guides the sperm to the ovaries

A

Myometrium contraction

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16
Q

What junction do sperm pass to enter the uterine tube

A

Uterotubal junction

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17
Q

What happens to the viscosity in the uterine tube as the sperm moves through it

A

Increases

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18
Q

What does the increasing viscosity do

A

Make it harder for sperm to swim

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19
Q

Where does most fertilisation occur

A

ampulla region of uterine tube

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20
Q

Describe the process that occurs for the egg to penetrate the egg

A

1) sperm goes through the cumulus cells that are around the oocyte
2) the sperm breaks the hyaluronic acid so the cumulus goes away
3) sperm binds to the zona pellucida via 4 glycoproteins
4) sperm undergoes acrosome reaction
5) sperm goes through zona pellucida
6) sperm enters the perevitelline space (gap between zona pellucida and oocyte plasma membrane)
7) equatorial segment of sperm head fuses with oocyte plasma membrane
8) the egg engulfs the sperm nucleus to form a vesicle
9) this causes an increase in calcium that triggers the stages of development

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21
Q

What is izumo

A

A protein on the sperm membrane involved in the fusion of egg membrane

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22
Q

When is izumo present

A

After the acrosome reaction of sperm

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23
Q

What is Juno

A

The receptor for izumo

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24
Q

Where is Juno located

A

On the oocyte plasma membrane

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25
Q

When a vesicle forms in the egg what triggers the calcium I increase

A

Phospholipase c zeta

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26
Q

What is phospholipase c zeta

A

A sperm specific enzyme

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27
Q

What is the purpose of a calicum influx when the sperm vesicle forms in the oocyte

A

Release of meiosis 2 block

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28
Q

Why do we need to complete meiosis 2 of the egg

A

So the egg is haploid and combined with the sperm nucleus that is already haploid

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29
Q

Describe the molecules involved in the meiotic block

A

1) usually a m-phase promoting factor (MPF) that is made of cyclin dependent kinase + cyclin B, blocks metaphase to anaphase transition
2) MPF is also stabilised by cytostatic factor (CSF)

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30
Q

What happens when there is an increased calcium to remove the meiotic block

A
  • Calcium suppresses CSF activity

- Calcium destroys Cyclin B by acitvating anaphase promoting complex (APC/C)

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31
Q

What other molecules apart from MPF hold the egg in meiotic arrest

A

Cohesion protein complex

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32
Q

How does the cohesion protein complex cause arrest in meiosis

A

Cohesion protein complex holds the sister chromatids together and resists the pulling force of microtubules

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33
Q

How can the cohesion protein complex become cleaved

A

By an enzyme known as seperase

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34
Q

Why is seperase enzyme inactive before fertilisation

A

Securin is bound to it

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35
Q

After fertilisation to remove the cohesion protein complex how is seperase activated

A

The anaphase promoting complex ubiquitinates securin so seperase is active and cleaves the cohesion protein complex

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36
Q

What are the 2 ways in stopping more than 1 sperm fertilising the egg

A

1) fast block

2) slow block

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37
Q

What is fast block

A

When the egg membrane depolarises after the sperm has entered

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38
Q

What is the slow block

A

Zona reaction

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39
Q

What is the zona reaction

A

A change in the zona pellucida due to cortical granules that release enzymes of proteases which clear the zona pellucida receptors on the egg

40
Q

What happens to Juno (egg membrane receptor)

A

Becomes shed with the cortical granules so sperm cannot fuse

41
Q

When the sperm and egg fertilise, what does the sperm bring

A

Haploid male genome

Centriole

42
Q

What does the haploid male genome determine

A

The sex of the baby

43
Q

What does the centriole allow

A

Spindle formation for first cell division

44
Q

What does the egg bring in fertilisation

A

Haploid female genome
Cytoplasma
All organelles
Mitochondria

45
Q

What has to happen to the sperm dna for it to get together with the female genetic material in the zygotic stage

A

DNA has to decondense

46
Q

Why does the male dna decondense in the zygotic stage

A

Because the dna is highly packed in the sperm

47
Q

After the sperm DNA has decondensed what happens to the male and female pronuclie

A

Replicate their dna

48
Q

How does the male and female pronuclie fuse

A

They migrate towards eachother

49
Q

What is the migration of the male and female pro nucleus guided by

A

Sperm aster ( a group microtubules radiating from the sperm centrosome)

50
Q

What occurs in syngamy

A

1) Pronuclear membranes break down
2) chromatin from both pronuclei intermixes on a spindle structure
3) nucleus involve reforms around zygote nucleus
4) cleavage (division) begins- marks end of fertilisation/begging of emrbyogenis

51
Q

Where does the embryo have to go to become implanted

A

Uterus

52
Q

What allows the transport of the embryo to the uterus

A

High level of progesterone

Cilia

53
Q

What does high levels of progesterone do to the muscles

A

Relax the muscles so the embryo can pass through tight junctions such as the isthmic spinchter

54
Q

What does cilia do

A

Move the uterus along the uterine tube to the uterus

55
Q

What is cleavage

A

The division of the zygote

56
Q

When does cleavage occur

A

As the embryo is travelling down to the uterus

57
Q

State the stages the zygote goes through in cleave

A 
Zygote 
2 blastomeres 
4 cell stage 
8 cell stage 
Morula (16-32 cells) ( at the end of the uterine tube)
58
Q

What controls the development up to the 2 cell stage

A

Oocyte cytoplasm

59
Q

What controls the development up to the 4 to 8 cell stage

A

Activation of genome to produce own proteins

60
Q

After the 8 cell stage what do we enter

A

Compaction

61
Q

What happens in compaction

A

Embryo becomes tightly compacted

62
Q

What forms before we get to the blastocyst stage

A

Trophoblast (outer layer) goes to from the placenta
Inner cell mass (inner cell) goes to form the embryoblast
Formation of fluid filled cavity called blastocoel

63
Q

When does blastocyst formation occur

A

After day 5 of fertilisation

64
Q

What hormone is produce at the blastocyst

A

HCG

65
Q

Which structures give HCG

A

Blastocoele

Trophoblast cells

66
Q

What happens after day 6

A

Hatching

67
Q

What does the hatching involve

A

1) Blastocyst expands the the zona pellucida through the abembroyonic pole
2) This allows embryo to squeeze out and blastocyst with trophoblast layer implants

68
Q

What are the 2 types of twins that we can have

A

Monozygotic

Dizygotic

69
Q

What increases the risk of dizygotic twins

A

Increased maternal age

IVF treatment

70
Q

What increases the risk of monozygotic twins

A

In vitro embryo culture

71
Q

What are the 4 types of monozygotic twins that we can get

A

Dichorinoic/diamniotic
Monochorionic/ diamnioatic
Monochorionic/ mono amniotic
Conjoined twins

72
Q

What is dichorionic/ diamniotic monozygotic twins

A

Twins that have own placenta and own amniotic sac

73
Q

What is monochorionic/diamniotic monozygotic twins

A

Twins that share own placenta and own amniotic sac

74
Q

What is monochorionic/mono amniotic

A

Twins that share own placenta and amniotic sac

75
Q

What is conjoined twins

A

Twins that are joined together

76
Q

What is the risk of monochorionic (same placenta)

A

Unequal blood flow

77
Q

What is the risk for monoamniotic (same aminotic sac)

A

Umbilical cord becoming tangled and compressed

78
Q

What are the 2 muscle layers of the uterus

A

Endometrium

Myometrium

79
Q

How many layers does the endometrium have

A

2

80
Q

What are the 2 layers of the endometrium

A

Upper functional layer

Low basal layer

81
Q

What does the upper functional layer do

A

Proliferate every month to give menstruation

82
Q

What is the basal layer of the endometrium attached to

A

Myometrium

83
Q

What are the cell types in the endometrium

A

Stromal matrix cells that contain spinal arteries

Luminal epithelial cells that line the stromal matrix

84
Q

What occurs in the proliferative/ follicular phase to the cells of the endometrial

A

The cells proliferate due to an increased oestrogen
Thickening of stromal cells
Increase of surface epithelium
Glandular invagination increase

85
Q

After ovulation what hormone is expressed

A

Progesterone

86
Q

What does progesterone stimulate in the secretory/ luteal phase

A

Secretion by glands that are in rich of glycogen, glycoproteins and amino acids for the nutrition to blastocyst

87
Q

What happens to the cells in the secretory/luteal phase

A

Stromal cell become larger

Spinal arteries fully develop

88
Q

At the end of the secretory/luteal phase what type of endometrium do we have

A

Receptive endometrium

89
Q

What does a receptive endometrium mean

A

Endometrium that is ready for implanting

90
Q

How many days does the window for implantation last for

A

4 days

91
Q

What is the window for implantation characterised by

A

Pinopodes

92
Q

What are pinopodes in the endometrium involved in

A

Absorption of the uterine fluid

93
Q

What does the absorption of the uterine fluid allow

A

Bringing the blastocyst blaster to the endometrium and immobilise it

94
Q

If there is no blastocyst what happens to the endometrium

A

Spiral artery constrict

Functional layer collapse and necrosis

95
Q

To allow menstruation what hormone level cause it

A

Decrease in progesterone

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