L06: Fertilisation

Question 1

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

Answer 1

Sperm

Egg

Question 2

Where does the sperm mature

Answer 2

In the male tract- epididymis

Question 3

What does capacitation of the sperm occur

Answer 3

In the female tract

Question 4

What meiosis is the egg after ovulation arrested at

Answer 4

Meiosis 2 metaphase 2

Question 5

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

Answer 5

Fimbrae

Question 6

What allows the egg to become picked up by the fimbrae

Answer 6

Follicular fluid in the oocyte that contains chemoattractants

Question 7

What allows the movement of the egg within the uterine tube

Answer 7

Muscle contracts

Question 8

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

Answer 8

Decreases

Question 9

What happens to the sperm in the upper vagina

Answer 9

Coagulates

Question 10

What cause the sperm to coagulate in the upper vagina

Answer 10

Semenogelin

Question 11

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

Answer 11

PSA (prostate specific antigen)

Question 12

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

Answer 12

The cervix

Question 13

When is the cervix least viscous

Answer 13

During 9-16 days of the cycle

Question 14

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

Answer 14

Sperm selection

Question 15

What guides the sperm to the ovaries

Answer 15

Myometrium contraction

Question 16

What junction do sperm pass to enter the uterine tube

Answer 16

Uterotubal junction

Question 17

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

Answer 17

Increases

Question 18

What does the increasing viscosity do

Answer 18

Make it harder for sperm to swim

Question 19

Where does most fertilisation occur

Answer 19

ampulla region of uterine tube

Question 20

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

Answer 20

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

Question 21

What is izumo

Answer 21

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

Question 22

When is izumo present

Answer 22

After the acrosome reaction of sperm

Question 23

What is Juno

Answer 23

The receptor for izumo

Question 24

Where is Juno located

Answer 24

On the oocyte plasma membrane

Question 25

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

Answer 25

Phospholipase c zeta

Question 26

What is phospholipase c zeta

Answer 26

A sperm specific enzyme

Question 27

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

Answer 27

Release of meiosis 2 block

Question 28

Why do we need to complete meiosis 2 of the egg

Answer 28

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

Question 29

Describe the molecules involved in the meiotic block

Answer 29

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)

Question 30

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

Answer 30

- Calcium suppresses CSF activity | - Calcium destroys Cyclin B by acitvating anaphase promoting complex (APC/C)

Question 31

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

Answer 31

Cohesion protein complex

Question 32

How does the cohesion protein complex cause arrest in meiosis

Answer 32

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

Question 33

How can the cohesion protein complex become cleaved

Answer 33

By an enzyme known as seperase

Question 34

Why is seperase enzyme inactive before fertilisation

Answer 34

Securin is bound to it

Question 35

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

Answer 35

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

Question 36

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

Answer 36

1) fast block | 2) slow block

Question 37

What is fast block

Answer 37

When the egg membrane depolarises after the sperm has entered

Question 38

What is the slow block

Answer 38

Zona reaction

Question 39

What is the zona reaction

Answer 39

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

Question 40

What happens to Juno (egg membrane receptor)

Answer 40

Becomes shed with the cortical granules so sperm cannot fuse

Question 41

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

Answer 41

Haploid male genome | Centriole

Question 42

What does the haploid male genome determine

Answer 42

The sex of the baby

Question 43

What does the centriole allow

Answer 43

Spindle formation for first cell division

Question 44

What does the egg bring in fertilisation

Answer 44

Haploid female genome Cytoplasma All organelles Mitochondria

Question 45

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

Answer 45

DNA has to decondense

Question 46

Why does the male dna decondense in the zygotic stage

Answer 46

Because the dna is highly packed in the sperm

Question 47

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

Answer 47

Replicate their dna

Question 48

How does the male and female pronuclie fuse

Answer 48

They migrate towards eachother

Question 49

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

Answer 49

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

Question 50

What occurs in syngamy

Answer 50

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

Question 51

Where does the embryo have to go to become implanted

Answer 51

Uterus

Question 52

What allows the transport of the embryo to the uterus

Answer 52

High level of progesterone | Cilia

Question 53

What does high levels of progesterone do to the muscles

Answer 53

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

Question 54

What does cilia do

Answer 54

Move the uterus along the uterine tube to the uterus

Question 55

What is cleavage

Answer 55

The division of the zygote

Question 56

When does cleavage occur

Answer 56

As the embryo is travelling down to the uterus

Question 57

State the stages the zygote goes through in cleave

Answer 57

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

Question 58

What controls the development up to the 2 cell stage

Answer 58

Oocyte cytoplasm

Question 59

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

Answer 59

Activation of genome to produce own proteins

Question 60

After the 8 cell stage what do we enter

Answer 60

Compaction

Question 61

What happens in compaction

Answer 61

Embryo becomes tightly compacted

Question 62

What forms before we get to the blastocyst stage

Answer 62

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

Question 63

When does blastocyst formation occur

Answer 63

After day 5 of fertilisation

Question 64

What hormone is produce at the blastocyst

Answer 64

HCG

Question 65

Which structures give HCG

Answer 65

Blastocoele | Trophoblast cells

Question 66

What happens after day 6

Answer 66

Hatching

Question 67

What does the hatching involve

Answer 67

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

Question 68

What are the 2 types of twins that we can have

Answer 68

Monozygotic | Dizygotic

Question 69

What increases the risk of dizygotic twins

Answer 69

Increased maternal age | IVF treatment

Question 70

What increases the risk of monozygotic twins

Answer 70

In vitro embryo culture

Question 71

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

Answer 71

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

Question 72

What is dichorionic/ diamniotic monozygotic twins

Answer 72

Twins that have own placenta and own amniotic sac

Question 73

What is monochorionic/diamniotic monozygotic twins

Answer 73

Twins that share own placenta and own amniotic sac

Question 74

What is monochorionic/mono amniotic

Answer 74

Twins that share own placenta and amniotic sac

Question 75

What is conjoined twins

Answer 75

Twins that are joined together

Question 76

What is the risk of monochorionic (same placenta)

Answer 76

Unequal blood flow

Question 77

What is the risk for monoamniotic (same aminotic sac)

Answer 77

Umbilical cord becoming tangled and compressed

Question 78

What are the 2 muscle layers of the uterus

Answer 78

Endometrium | Myometrium

Question 79

How many layers does the endometrium have

Answer 79

2

Question 80

What are the 2 layers of the endometrium

Answer 80

Upper functional layer | Low basal layer

Question 81

What does the upper functional layer do

Answer 81

Proliferate every month to give menstruation

Question 82

What is the basal layer of the endometrium attached to

Answer 82

Myometrium

Question 83

What are the cell types in the endometrium

Answer 83

Stromal matrix cells that contain spinal arteries | Luminal epithelial cells that line the stromal matrix

Question 84

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

Answer 84

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

Question 85

After ovulation what hormone is expressed

Answer 85

Progesterone

Question 86

What does progesterone stimulate in the secretory/ luteal phase

Answer 86

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

Question 87

What happens to the cells in the secretory/luteal phase

Answer 87

Stromal cell become larger | Spinal arteries fully develop

Question 88

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

Answer 88

Receptive endometrium

Question 89

What does a receptive endometrium mean

Answer 89

Endometrium that is ready for implanting

Question 90

How many days does the window for implantation last for

Answer 90

4 days

Question 91

What is the window for implantation characterised by

Answer 91

Pinopodes

Question 92

What are pinopodes in the endometrium involved in

Answer 92

Absorption of the uterine fluid

Question 93

What does the absorption of the uterine fluid allow

Answer 93

Bringing the blastocyst blaster to the endometrium and immobilise it

Question 94

If there is no blastocyst what happens to the endometrium

Answer 94

Spiral artery constrict | Functional layer collapse and necrosis

Question 95

To allow menstruation what hormone level cause it

Answer 95

Decrease in progesterone