Fertilization

Question 1

Know the important events involved in fertilization

Answer 1

1. Capacitation
2. Sperm penetration between cumulus cells
3. Sperm attachment to zona pellucida
4. Sperm penetration to zona pellucida
5. Fusion of sperm and oocyte membranes

Question 2

Supplementary sperm

Answer 2

-Extra sperm pass through the Zona Pellucida into the Perivitelline space
-May not cause issues

Question 3

Supernumerary sperm

Answer 3

-Extra sperm which succeed in entering the Vitellus
-Such ova are said to show polyspermy

Question 4

Know the different types of twins and how they come to be

Answer 4

-Monozygotic
-Dizygotic

Question 5

Monozygotic

Answer 5

-A fertilized single egg splits into two developing zygotes
-Very early stage
-Identical twins
-Same sex

Question 6

Dizygtic

Answer 6

-Result from the fertilization by two sperm of two separate ova that have reached maturation at the same time
-Not identical twins
-Can be different sexes
-Incidence increases with age of mother

Question 7

Know the characteristics of the cumulus cells in the cumulus-oocyte complex.

Answer 7

-Embedded in an Extracellular Matrix (ECM)
-Contains hyaluronic acid

Question 8

Know the purposes/characteristics of ZP-1, ZP-2 and ZP-3

Answer 8

-ZP1: Structural support
-ZP2: Helps an acrosome reacted sperm move through the zona
-ZP3: Binds to a receptor on the sperm plasma membrane and induces the acrosome reaction

Question 9

Know how the acrosome reaction progresses

Answer 9

1. Sperm contacts the Zona Pellucida
2. Perforations develop on acrosome
3. Plasma membrane fuses with the outer acrosomal membrane and creates point fusions.
   -Enzymes can escape and enables sperm to penetrate the Zona Pellucida
   ~Modifies equatorial segment so that it can later fuse with plasma membrane of oocyte
4. The vesicles then slough and leave other structures intact including the Inner acrosomal membrane, Equatorial segment, and Post nuclear cap
5. Zona Pellucida remains mostly intact

Question 10

Know steps of fertilization following acrosome reaction

Answer 10

1. Proacrosin converts to acrosin by Acrosin hydrolyzes Zona proteins
2. Sperm enters Perivitelline space and settle into bed of microvilli
3. Plasma membrane of oocyte fuses with membrane of equatorial segment and Polyspermy is blocked

Question 11

Know what happens after sperm is engulfed

Answer 11

-2nd meiotic division is completed
-Sperm nucleus de-condenses and disulfide cross-linking is reduced by glutathione
-Male pronucleus forms
-Syngamy occurs

Question 12

Define/describe syngamy

Answer 12

-The fusion of the egg and sperm pronuclei to form a diploid zygote
-Membranes of the pronuclei break down
-Chromosomes condense and arrange themselves for mitotic cell division
-On membrane dissolution there is one diploid (2n) cell
-First cleavage follows shortly and leaves two cells each with 2n chromosomes

Question 13

Know some examples of how fertilization can go away

Answer 13

-Too many sperm
-Infertility
-Bad timing
-Ectopic pregnancy

Question 14

How does too many sperm cause fertilization to go away?

Answer 14

-Dispermy
-Triploidy
-Leads to spontaneous abortion: Most cases

Question 15

How does bad timing cause fertilization to go away?

Answer 15

-Most sperm can only survive 48 hours within the female genital tract
-In vitro studies show the ovulated egg cannot be fertilized after 24 hours

Question 16

How does cause ectopic pregnancy fertilization to go away?

Answer 16

-Fertilization occurs outside the oviduct
-Implantation may occur in the wrong location
-If oviducts are scarred fertilized ovum may implant in the fallopian tube

Question 17

Know what polyspermy is and why it is important to block it.

Answer 17

-The fertilization of an egg by multiple sperm.
-Extra sperm entered the vitellus
-These embryos almost always abort

Question 18

How is polyspermy blocked?

Answer 18

-Zona block
-Vitelline block

Question 19

Zona Block

Answer 19

-Cortical granule components alter zona receptors
-Other sperm can’t penetrate zona
-Slow block
-Most important in sheep, cows, pigs, and dogs

Question 20

Vitelline block

Answer 20

-Cortical granules fuse to vitelline membrane
-Becomes less penetrable to sperm
-Fast
-Most important in rabbits

Question 21

In what species is zina and vitelline block equally important?

Answer 21

In rats and mice

Question 22

Know factors that reduce the effectiveness of the block to polyspermy

Answer 22

-Age of ova
-Heat (temp)
-Excessive sperm numbers

Question 23

How does age of ova reduce the effectiveness to block polyspermy

Answer 23

-Time of insemination relative to ovulation
-Aged oocyte increases chance of polyspermy

Question 24

How does heat reduce the effectiveness to block polyspermy

Answer 24

-Increases metabolism and lifespan of egg
-Fever or Environment effect on body temperature

Question 25

How does excessive sperm numbers reduce the effectiveness to block polyspermy

Answer 25

Previous barriers were ineffective