L2: Fertilization Flashcards
Egg
Large (~100 μm)
Round, symmetrical, nonmotile cell
arrested i metaphase 2 of meiosis
microvilli in the surface
Glycoprotein coat acting as a barrier to the sperm
Zona pellucida
3 layers covering an egg
Corona radiata
Zona pellucida
Vitelline membrane
Sperm
small, asymmetrical and motile cell
end product of spermatogenesis
3 Components of Sperm
Tail
Midpiece
Head with Acrosome
also referred to as principal piece that contains the flagellar apparatus and is what makes the cell motile
Tail
contains mitochondria and helps in propelling
Midpiece
lysosomal-like compartment derived from the Golgi Apparatus; contains soluble hyrdolases
Head c Acrosome
Fertilization
process by which the sperm and secondary oocyte fuse
where does fertilization occur
ampullary region of uterine tube (widest part of tube)
how much spermatozoa is deposited in vagina during intercourse
2-5 million
life span of sperm in female reproductive tract
3-7 days
at day 14 after the last day of menstrual period, what are the 2 hormones seen
(1) follicle stimulating hormone/FSH (releases follicle that has the egg inside)
(2) luteinizing hormone/LH (increases progesterone, making the uterus lining thick)
what propels the egg
fimbriae and mucus
percentage of spermatozoa that successfully meets the egg
1%
subject to physical stress d/t:
Ejaculation
Contractions in female tract
Change in pH environment
Mucous secretions
Defenses of female immune system
Anatomy of the fallopian tube (double tract,narrower)
Ovulation
sperm become motile again
spermatozoa has to undergo ___ & ___ to acquire the capability to fertilize the oocyte
Capacitation
Acrosome Reaction
Capacitation
period of conditioning in female reproductive tract that lasts ~7 hrs
a glycoprotein coat & seminal plasma proteins are removed from plasma membrane overlying the acrosomal region of the spermatozoa
capacitated sperm = can pass through corona cells = undergo acrosome reaction
bicarbonate ions enter sperm & hyperpolarizes sperm’s plasma membrane affecting the motility of sperm
Acrosome Reaction
membrane surrounding acrosome dissolves to fuse c plasma membrane (of sperm head) releasing contents of acrosome
has antigen for binding to cell membrane of egg & lytic enzyme
occurs after binding to the zona pellucida
induced by zona proteins
Hyaluronidase
assists in penetration of corona radiata barrier
Trypsin-like substance
needed for digestion of zona pellucida
Acrosin
needed to help cross the zonal pellucida
once sperm enters, the oocyte proceeds to ___
meiosis 2
Spermatozoa dies within ___ of their release
24 hrs
Trip of spermatozoa from uterus to cervix lasts
30 mins to 6 days
Oocyte travel via ___ & ___
ciliary beat
rhythmical contraction of muscle of tube
Phases of Fertilization
- Penetration of Corona Radiata
- Penetration of Zona Pellucida
- Fusion of oocyte and sperm cell membranes
Phase 1: Penetration of the Corona Radiata
only 300 to 500 (out of 200 - 300 M spermatozoa) reach the site of fertilization
only one fertilizes the egg
others aid fertilizing sperm in penetrating barriers protecting the female gamete
capacitated sperms pass freely through coronal cell
Zona Pellucida
glycoprotein shell surrounding the egg
facilitates and maintains sperm binding & induces acrosome reaction
has 5 zones
Phase 2: Penetration of the Zona Pellucida
occurs in ZP3 of Z Pellucida
release of acrosomal enzymes (acrosin) allows sperm to penetrate zona = coming in contact c plasma membrane of oocyte
results in release of lysosomal enzymes from cortical granules lining the plasma membrane of oocyte & alters properties of ZP (zona reaction) to prevent sperm penetration (block to polyspermy)
Phase 3: Fusion of Oocyte and Sperm Membranes
initial adhesion of sperm to oocyte is mediated in part by the interaction of integrins on the oocyte and their ligands, disntegrins, on sperm
after adhesion, plasma membranes of sperm and egg fuse
in humans, both head and tail of spermatozoon enter cytoplasm of oocyte, but plasma membrane is left behind on oocyte surface
Path of Sperm Cell
- Corona Radiata
- Zona Pellucida
- Plasma membrane of secondary oocyte
- Cytoplasm of secondary oocyte
Egg Response: Cortical and Zona Reactions
as a result of the release of cortical oocyte granules, which contain lysosomal enzymes: (1) oocyte membrane becomes impenetrable to other sperm, (2) zona pellucida alters its structure and composition to prevent sperm binding and penetration
these reactions prevent polyspermy (penetration of more than one spermatozoon into oocyte)
Egg Response: Resumption of the Second Meiotic Division
oocyte finishes its second meiotic division immed. after entry of spermatozoon
product: 2 daughter cells
its chromosomes (22+X) arrange themselves in a vesicular nucleus (female pronucleus)
Egg Response: Metabolic Activation of the Egg
spermatozoon moves forward until it lies close to the female pronucleus
nucleus becomes swollen and forms the male pronucleus, the tail detaches and degenerates
male and female pronuclei are: indistinguishable and lose their nuclear envelopes; both haploid and replicate its DNA
chromosome organize in the spindle in preparation for normal mitotic division
Results of Fertilization
Restoration of the Diploid Number of Chromosomes
Determination of the Sex of the New Individual
Initiation of Cleavage
Zygote
fertilized ovum
Results of Fertilization: Restoration of the Diploid Number of Chromosomes
half from father, half from mother
zygote contains new combination of chromosomes different from both parents
Results of Fertilization: Determination of the Sex of the New Individual
X-carrying sperm produces female (XX) embryo; Y-carrying sperm produces a male (XY) embryo
chromosomal sex of embryo is determined at fertilization
Results of Fertilization: Initiation of Cleavage
without fertilization, oocyte usually degenerates 24 hrs aft ovulation
