Fertilisation, Assisted Reproduction and Contraception

Question 1

What is the function of the zona pellucida?

Answer 1

• Ensures species specific recognition (juno receptor only recognizes lzumo1 in humans)
• Prevents polyspermy (zona block and membrane block-juno is shed)
• Protects preimplantation embryo from reabsorption

zona pellucida coats the ovulated secondary oocyte

Question 2

What is the function of cumulus cells?

Answer 2

Secrete paracrines to oocyte that help each other grow (ie GF)
Connected to oocyte through zona pellucida
VERY important in oocyte maturation

Question 3

What barriers in females ensure only the best sperm fertilize the egg?

Answer 3

1. Vagina: is acidic so most die swimming or leaking out
2. Cervical mucus is hard to penetrate (but high estrogen during ovulation thins it)
3. Zona pellucida: has to bind and penerate it
4. Oocyte membrane: has to bind and fuse -> ensures only ONE sperm fertilizes
5. Time: sperm only viable 48 hr and oocyte 6-24 hr

Question 4

What is capacitation?

Answer 4

Sperm loses cholesterol, phospholipids, glycoproteins
Becomes less stable (reduces lifespan)
Hyperactivation (corkscrew swimming=viable)

happens in oviduct

Question 5

What are the three stages of fertilization?

Answer 5

1. Capacitation and Acrosome reaction (sperm prep)
2. Sperm binding and fusion
3. Cortial reaction (preventing polyspermy)

Question 6

What is acrosome reaction?

Answer 6

Fusion of sperm and outer acrosomal membrane
Acrosome has proteolytic enzymes that get released: hyaluronidase, acrosin, trypsin
Expresses surface molecules for sperm to bind ZP (lzumo1)

hyaluronidase is for getting through zona pellucida

Question 7

What is the cortical reaction?

Answer 7

Cortical granules fuse with plasma membrane, contents released into perivitelline space
This changes ZP structure which prevents other sperm from entering
Zona block (slow, ZP2 cleaved) and membrane block (juno receptor shed)

Question 8

What is compaction and when does it happen?

Answer 8

• Begins at 16-cell stage
• Spherical cells become flattened
• E-cadherin and B-catenin bring all cells together

Question 9

What is polarization and when does it happen?

Answer 9

• Each cell becomes epithelial like and polarized (eg all nuclei towards center)
• Tight junctions form
• Morulla formation (32 cell stage)

Question 10

How does blastocyst formation happen and when does it happen?

Answer 10

Large cavity forms and inner cells pushed to one side (Na pumped into cavity so water is drawn into it)
Inner cells= embryo
Outer cells= trophectoderm (placenta)
Happens after morulla (ie after compaction and polarization)

Question 11

When does the zona pellucida leave the blastocyst?

Answer 11

1-2 days after entering uterus (Day 6-7 post ovulation)

Question 12

What is a vasectomy?

Answer 12

removal of apart of the vans deferens
sperm production does not cease just its passage to the penis

Question 13

What is a diaphragm contraceptive?

Answer 13

acts like a reservoir for spermacides
Contains nonxinol-9 (detergent- destroys membranes)

Question 14

How does the combined oral contraceptive pill work?

Answer 14

Progesterone - supresses ovulation (HPA axis), Thickens cervical mucus
Estrogen- enhances effects of progesterone

Question 15

How does the mini oral contraceptive pill work?

Answer 15

Progesterone only
Thickens cervical mucus

Question 16

What is the hormonal implant?

Answer 16

Inhibit ovulation by thickening cervical mucus and endometrium

Question 17

How does the hormonal injection work?

Answer 17

Progestogens injected every 12-8 weeks

Question 18

How does the morning after pill work?

Answer 18

Levonorgestrel: prevents LH surge to delay ovulation (only effective before day 10 of 28 menstrual cycle)
Ulipristal acetate: selective progesterone receptor modulator - prevents follicular rupture (only effective before day 13 of menstrual cycle)

Question 19

What effect do exogenous testosterone and progestogen have on certain hormones?

in reference to male contraception

Answer 19

They SUPRESS FSH, LH, and GnRH

Question 20

What hormone is measured to ensure ovaries are working properly?

Answer 20

Progesterone

Question 21

If testicles were not making sperm, what would the FSH levels look like?

Answer 21

FSH would be very high

Question 22

When trying to extract eggs from ovary, are high FSH levels a good or bad thing?

Answer 22

If FSH levels are HIGH then have to use donor eggs

Question 23

Why dont you get a period when you get pregnant?

Answer 23

Progesterone levels dont fall so period doesnt start
HCG keeps corpus luteum alive for 8-10 weeks, then placenta makes its own progesterone

corpus luteum secretes progesterone

Question 24

Which hormone promotes endometrium growth?

Answer 24

Estradiol
Progesterone stops endometrium growth