Fertilisation and the Luteal Phase

Question 1

Why is the semen coagulated?

Answer 1

to avoid loss of sperm

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

Question 2

Can freshly ejaculated sperm fertilise an egg?

Answer 2

no

Question 3

How is the semen liquified?

Answer 3

similar cascade thrombolysis

Question 4

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

Answer 4

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

Question 5

What are cervical crypts?

Answer 5

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

Question 6

Within how many days does fertilisation occur?

Answer 6

1-2 days

5 days sperm can survive in the female reproductive tract

Question 7

How does the sperm swim to the egg?

Answer 7

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

Question 8

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

Answer 8

tail beating= increased frequency and increased amplitude

Question 9

What kind of channels do sperms have?

Answer 9

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

Question 10

How many hours after ejaculation are the sperm fertile?

Answer 10

4 hours to 18 hours

Question 11

What makes the sperm fertile?

Answer 11

capacitation

Question 12

Why does capacitation occur?

Answer 12

so the role of acrosome doesn’t take place early

Question 13

What is capacitation?

Answer 13

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

Question 14

What is the acrosome reaction?

Answer 14

when sperm comes into contact with egg

acrosome bursts and enzymes break down zona pelucida

Question 15

What enzymes are involved with the acrosome reaction?

Answer 15

Hyaluronidase- dissolves through Zona Pelucida

Acrosin- bound to inner acrosomal membrane digests Zona Pelucida

Question 16

What signals the ovary to begin ovulation?

Answer 16

LH surge

Question 17

After ovulation, what does the oocyte complete?

Answer 17

meiosis I

Question 18

What does the oocyte extrude after completing meiosis I?

Answer 18

polar body

Question 19

What is a polar body?

Answer 19

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

Question 20

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

Answer 20

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

Question 21

How is the corpus luteum formed?

Answer 21

mixing of granulosa and theca cells

Question 22

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

Answer 22

Proliferation of endometrium= thickens the endometrium

Question 23

What happens in the differentiation of the endometrium?

Answer 23

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

Question 24

What does progesterone do to cilia?

Answer 24

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

Question 25

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

Answer 25

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

Question 26

When the corpus luteum dies, what happens?

Answer 26

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

Question 27

How does the corpus luteum die?

Answer 27

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

Question 28

What is hCG similar to?

Answer 28

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

Question 29

What is the corona radiata?

Answer 29

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

Question 30

What are the cumulus oophorus cells?

Answer 30

outside corona radiata granulosa cells loosely packed secrete mucus

Question 31

What is Zona Pelucida?

Answer 31

glycoprotein

Question 32

What is the perivitelline space?

Answer 32

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.

Question 33

What does the sperm bind to on zona pelucida?

Answer 33

receptor adhesion molecules (ZP3) | interaction between sperm and zona pelucida is SPECIES SPECIFIC

Question 34

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

Answer 34

through phagocytosis

Question 35

What happens to the sperm tail?

Answer 35

it is destroyed | if it enters the egg, it is destroyed

Question 36

What is released from the sperm membrane?

Answer 36

Phospholipase Z

Question 37

How does PLZ act?

Answer 37

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

Question 38

What is the cortical reaction?

Answer 38

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

Question 39

What do proteases do?

Answer 39

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

Question 40

What does peroxides do?

Answer 40

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)

Question 41

The Ca2+ released in the egg causes what?

Answer 41

triggers the egg to complete meiosis II

Question 42

What are the catsper channels?

Answer 42

``` 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 ```

Question 43

Explain the whole process of syngamy:

Answer 43

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