Fertilization Flashcards
where does fertilization occur
ampullary region of the uterine tube (widest part and closest to the ovary)
where does the sperm enter the female reproductive system from first
cervix
why do sperm become motile at ovulation
because of chemoattractants produced by cumulus cells surrounding the egg
Spermatozoa are not able to fertilize the oocyte
immediately upon arrival in the female genital tract but
must undergo
1. ____________
2. ____________
- capacitation
2. the acrosome reaction to acquire this capability
what is capacitation
period of conditioning in the female reproductive tract
why is speeding to the ampulla not an advantage
capacitation has not yet occurred so such sperm are not capable of fertilizing the egg
what happens during capacitation
a glycoprotein coat and seminal plasma proteins are removed from the plasma membrane that overlies the acrosomal region of the spermatozoa
only ______________ can pass through the corona cells and undergo the acrosome reaction
capacitated sperms
what induces acrosome reaction
zona proteins, ZP3
what are the 3 phases of fertilization
Phase 1, penetration of the corona radiata
Phase 2, penetration of the zona pellucida
Phase 3, fusion of the oocyte and sperm cell membranes
what is the function of the zona
a glycoprotein shell surrounding the egg that facilitates and maintains sperm binding and induces the acrosome reaction
what allows the sperm to penetrate the zona
Release of acrosomal enzymes (acrosin) allows sperm to penetrate the zona
what does the sperm coming into contact with the plasma membrane lead to
release of lysosomal enzymes from cortical granules lining the plasma membrane of the oocyte
why do the enzymes alter the properties of the zona pellucida
to prevent sperm penetration and inactivate species-specific receptor sites for spermatozoa on the zona surface
what mediates the initial adhesion of sperm to the oocyte
interaction of integrins on the oocyte and their ligands, disintegrins, on sperm
what happens after adhesion
the plasma membranes of the sperm and egg fuse
how does the egg respond after the spermatozoa enter the oocyte
- Cortical and zona reaction
- Resumption of the second meiotic division
- Metabolic activation of the egg
how does the zona pellucida prevent sperm binding and penetration
altering its surfacen and composition preventing polyspermy
what is another way of preventing polyspermy
oocyte membrane becomes impenetrable to other spermatozoa
The oocyte finishes its _________ immediately after entry of the spermatozoon. One of the daughter cells, which receives hardly any _____, is known as the __________, the other daughter cell is the ___________
second meiotic division
cytoplasm
second polar body
definitive oocyte.
where do chromosomes (22+X) arrange themselves during Resumption of the second meiotic division
in a vesicular nucleus known as the female pronucleus
what probably carries the activation factor during Metabolic activation of the egg
spermatozoon
Within the cytoplasm of the oocyte, the nucleus of the sperm __________________. The tail of the sperm _________________. During growth, the male and female pronuclei _______________
Within the cytoplasm of the oocyte, the nucleus of the sperm enlarges to form the male pronucleus. The tail of the sperm degenerates. During growth, the male and female pronuclei replicate their DNA
what three events occur during Metabolic activation of the egg
- Condensation of the chromosomes,
- Arrangement of the chromosomes for mitotic cell division
- First cleavage division of the zygote occur
what are the main results of fertilization
- Restoration of the diploid number of chromosomes
- Determination of the sex of the new individual
- Initiation of cleavage
- Without fertilization, the oocyte usually degenerates 24 hours after ovulation
during mitotic division of the zygote, what forms?
blastomeres
what happens 3 days after fertilization
embryo divides again to form a 16-cell morula (mulberry)
what do the inner cell mass and the outer cell mass of the morula form
The inner cell mass gives rise to tissues of the embryo proper, and the outer cell mass forms the trophoblast, which later contributes to the placenta
how does the blastocystic cavity form during blastocyst formation
Shortly after the morula enters the uterus uterine fluid
passes through the zona pellucida to form a fluid -filled space —the blastocystic cavity— inside the morula
as the fluid increases in the blastocystic cavity, what does the blastomere separate into
The trophoblast, the thin outer cells that give rise to the embryonic part of the placenta
The embryoblast, a discrete group of blastomeres that is the primordium of the embryo
implantation begins after the _______________ as disappeared
zona pellucida. its shedding allows the blastocyst to increase rapidly in size
what do the embryoblast and the trophoblast do
the embryoblast projects into the blastocystic cavity and the trophoblast forms the wall of the blastocyst
where does the blastocyst nourishment from
secretions of the uterine glands
after 6 days where does the blastocyst attach
to the endometrial epithelium
what mediates initial attachment of the blastocyst to the uterus
L-selectin on trophoblast cells and its carbohydrate receptors on the uterine epithelium
what do Integrin receptors for laminin and fibronectin promote
attachment and migration respectively
what layers does the trophoblast proliferate and differentiate into after the blastocyst binds to the epithelium
The cytotrophoblast, the inner layer of trophoblast cells
The syncytiotrophoblast the outer layer consisting of
a multinucleate protoplasmic mass formed by the fusion of cells of trophoblast
when does the secretory phase begin
approximately 2 to 3 days after ovulation in response to progesterone produced by the corpus luteum
what happens to the uterine glands and arteries during the secretory phase
they become coiled and the tissue becomes succulent
what are the three distinct layers can be recognized in the endometrium due to the coiling of the uterine glands and arteries
a superficial compact layer, an intermediate spongy layer, and a thin basal layer
where does the blastocyst implant along the endometrium
anterior or posterior wall of the body of the uterus where it becomes embedded between the openings of the glands
what parts of the endometrium shed during menstruation
compact and spongy layers
what happens to the venules and sinusoidal spaces when fertilization doesn’t occur
gradually become packed with blood cells, and an extensive diapedesis of blood into the tissue is seen
what is the functions of the basal arteries (arteries in the basal layer of the endometrium)
functions as the regenerative layer in the rebuilding of glands and arteries in the proliferative phase
what are causes of female infertility
occluded uterine tubes (most commonly caused by pelvic inflammatory disease), hostile cervical mucus, immunity to spermatozoa, absence of ovulation
what is
a) oligozoospermia
b) azoospermia
a) ejaculate contains very few live sperm
b) no live sperm
what can overcome oligozoospermia and azoospermia
intracytoplasmic sperm injection (a single sperm is injected into the cytoplasm of the egg to cause fertilization)
when is intracytoplasmic sperm injection not useful
infertility resulting from blocked uterine tubes or oligospermia (reduced number of sperms)
