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Flashcards in Fertilization Deck (27):

What is fertilization?

the event that sees a single sperm nucleus unite with the egg nucleus within the activated oocyte cytoplasm


What surrounds the oocyte?

-vitelline membrane
-perivitelline space
-zona pellucida
-cumulus oophorus (granulosa cells)


Explain the transport of the oocyte

-upon ovulation, oocyte picked up by fimbria of oviduct and transported through the infundibulum to the ampulla
-on entry to the ampulla, it immediately attaches to the oviductal epithelium

(vital that oocyte is still contained within its expanded cumulus matrix during transport)


What is capacitation?

maturational changes sperm undergo in the female tract (acquire capacity to bind to and fertilize the egg)


What is involved with capacitation?

1. removal or modification of proteins that were acquired by the sperm during epididymis passage
2. lowering of cholesterol/phospholipid ratio of sperm plasma membrane
3. hyperpolarization of membrane resting potential in region overlaying acrosome
4. aggregation of lipid microdomains of plasma membrane that contain zona pellucida-binding protein complexes
5. phosphorylation of surface tyrosine residues


Capacitation is speculated to be mediated by changes in what?

1. hormone milieu
2. contents of the oviductal lumen from the ovulated follicular fluid
3. increasing oviductal fluid bicarbonate concentration


What is hyperactivated motility?

increased amplitude of tail movement which also causes side-side movement of the head


What is the function of hyperactivated motility?

detaching sperm from oviductal reservoir
locating the egg
penetration of outer egg coats


What are the 2 thoughts on why capacitation occurs?

1. events surrounding ovulation signal oviductal epithelium to secrete something that triggers capacitation
2. capacitation occurs because of changing conditions as they move up the oviduct


Do sperm have a shorter lifespan once they go through capacitation?



How does the sperm find the oocyte in non-mammalians?


oocyte secretes substances that effect intracellular calcium levels in the sperm (low calcium causes linear swimming and sperm continue up attractant concentration gradient towards egg)


How does the sperm find the oocyte in mammals?

thermotaxis at long distances
some chemotaxis at short distances


How do sperm penetrate the cumulus oophorus?

only capacitated sperm can penetrate the cumulus oophorus because of hyperactivated motility

also have hyaluronidase, which helps break down the hyaluronic acid matrix of the cumulus oophorus


How do sperm penetrate the zona pellucida?

capacitated sperm bind to ZP and undergo acrosome reaction


What is the acrosome reaction?

fusion of outer acrosomal membrane with the plasma membrane of the sperm resulting in exposure of acrosomal content to extracellular environment


What 2 substances are thought to induce the acrosome reaction?

the ZP itself


Binding to the ZP causes a rapid increase in cytosolic calcium in the sperm resulting in what?

1. sperm plasma membrane fuses at multiple points with outer acrosomal membrane causing membrane vesiculation
2. acrosomal contents released, exposing inner acrosomal membrane
3. inner acrosomal membrane binds to ZP2 (glycoprotein on ZP)


What happens to the sperm after the acrosome reaction and binding to the ZP?

-sperm plasma membrane fuses with vitelline membrane, which wells up to surround the sperm
-sperm is now incorporated into the ooplasm
-membrane then breaks down and the sperm nucleus is released into the egg cytoplasm


What are the contributions of the sperm to the next generation?

1. paternal haploid genome
2. signal to initiate egg metabolism/activation
3. centrosome


What happens when the egg is activated?

1. escapes 2nd meiotic arrest
2. undergoes the cortical reaction


How does the sperm increase calcium in the oocyte?

introduces a soluble sperm-derived factor (oscillin/oscillogen) that enhances the calcium-induced calcium release from intracellular stores

(calcium triggers entry into meiosis)


What is the male pronucleus?

upon entering the ooplasm, the sperm head separates from the tail and the nuclear membrane degenerates and a new nuclear envelope is formed around it


What is the female pronucleus?

following completion of 2nd meiosis, the female chromatin is decondensed and acquires a nuclear envelope


What is pronuclear migration?

male and female pronuclei are directed towards the center of the cell


What occurs in syngamy?

chromatin in each pronucleus duplicates and condenses and the nuclear membranes break down


Name 3 methods of avoiding polyspermy

1. limiting the number of sperm at the site of fertilization
2. cortical granules of the ooplasm fuse with the vitelline membrane, discharging their enzymatic contents into the perivitelline space (cause zona hardening)
3. vitelline or membrane block (sperm cannot bind or fuse to vitelline membrane)


How does triploidy occur?

1. failure of polyspermy block
2. failure to extrude the 2nd polar body