Fertilization Flashcards
Know the important events involved in fertilization
- Capacitation
- Sperm penetration between cumulus cells
- Sperm attachment to zona pellucida
- Sperm penetration to zona pellucida
- Fusion of sperm and oocyte membranes
Supplementary sperm
-Extra sperm pass through the Zona Pellucida into the Perivitelline space
-May not cause issues
Supernumerary sperm
-Extra sperm which succeed in entering the Vitellus
-Such ova are said to show polyspermy
Know the different types of twins and how they come to be
-Monozygotic
-Dizygotic
Monozygotic
-A fertilized single egg splits into two developing zygotes
-Very early stage
-Identical twins
-Same sex
Dizygtic
-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
Know the characteristics of the cumulus cells in the cumulus-oocyte complex.
-Embedded in an Extracellular Matrix (ECM)
-Contains hyaluronic acid
Know the purposes/characteristics of ZP-1, ZP-2 and ZP-3
-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
Know how the acrosome reaction progresses
- Sperm contacts the Zona Pellucida
- Perforations develop on acrosome
- 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 - The vesicles then slough and leave other structures intact including the Inner acrosomal membrane, Equatorial segment, and Post nuclear cap
- Zona Pellucida remains mostly intact
Know steps of fertilization following acrosome reaction
- Proacrosin converts to acrosin by Acrosin hydrolyzes Zona proteins
- Sperm enters Perivitelline space and settle into bed of microvilli
- Plasma membrane of oocyte fuses with membrane of equatorial segment and Polyspermy is blocked
Know what happens after sperm is engulfed
-2nd meiotic division is completed
-Sperm nucleus de-condenses and disulfide cross-linking is reduced by glutathione
-Male pronucleus forms
-Syngamy occurs
Define/describe syngamy
-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
Know some examples of how fertilization can go away
-Too many sperm
-Infertility
-Bad timing
-Ectopic pregnancy
How does too many sperm cause fertilization to go away?
-Dispermy
-Triploidy
-Leads to spontaneous abortion: Most cases
How does bad timing cause fertilization to go away?
-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
How does cause ectopic pregnancy fertilization to go away?
-Fertilization occurs outside the oviduct
-Implantation may occur in the wrong location
-If oviducts are scarred fertilized ovum may implant in the fallopian tube
Know what polyspermy is and why it is important to block it.
-The fertilization of an egg by multiple sperm.
-Extra sperm entered the vitellus
-These embryos almost always abort
How is polyspermy blocked?
-Zona block
-Vitelline block
Zona Block
-Cortical granule components alter zona receptors
-Other sperm can’t penetrate zona
-Slow block
-Most important in sheep, cows, pigs, and dogs
Vitelline block
-Cortical granules fuse to vitelline membrane
-Becomes less penetrable to sperm
-Fast
-Most important in rabbits
In what species is zina and vitelline block equally important?
In rats and mice
Know factors that reduce the effectiveness of the block to polyspermy
-Age of ova
-Heat (temp)
-Excessive sperm numbers
How does age of ova reduce the effectiveness to block polyspermy
-Time of insemination relative to ovulation
-Aged oocyte increases chance of polyspermy
How does heat reduce the effectiveness to block polyspermy
-Increases metabolism and lifespan of egg
-Fever or Environment effect on body temperature
How does excessive sperm numbers reduce the effectiveness to block polyspermy
Previous barriers were ineffective
