L3: Ovulation, Fertilization & Implantation Flashcards
What controlled human Sexual cycles?
Hypothalamus which produce GnRH
How does the hypothalamus controls the Sexual cycles?
Because it acts on cells of the anterior pitiutary gland > which secrete gonadotropins (LH&FSH) > puberty
The ovarian cycle: (the phases are)
- Follicular phase
- ovulation
- luteal phase
What is the role LH & FSH in female ovarian cycles?
• stimulate and control cyclic changes in the ovary
What stimulates the primary-stage (preantral ) follicles? (Follicular phase)
the influence of FSH
How many primary-stage (preantral ) follicles are stimulated?
15 to 20
What is the result at the end of the follicular phase?
Only one of these follicles will reach full maturity the others degenerate and become atretic and replaced by connective tissue forming corpus atreticum.
How is the proliferation of the granulosa mediated?
by growth differentiation factor 9 > GDF9
define growth differentiation factor 9 (GDF9)
- a member of the transforming growth factor beta
* important to change the secondary follicle to a pre-antral follicle
GDF9 require what for the conversion
This requires FSH, activins, inhibin, androgens, estrogen, GDF9, BMP15
What is the function of Cumulus cells
continuously supplying the cell with hormones + secreting chemoattractant for the sperm
What is the importance of the granulosa cells?
Nourish the oocyte with hormones mainly estrogen.
What is the role of AMH? (anti-Mullerian hormone)
Inhibition follicles allowing only one to mature > regulation of ovarian follicle growth.
How does Theca interna and granulosa cells produce estrogens?
theca interna cells produce > androstenedione and testosterone > and granular cells convert these hormones to > estrone and 17-beta estradiol.
what happens after estrone & 17-beta estradiol production?
Uterine endometrium enters the proliferative phase
what happens to the uterus in the proliferative phase?
There is significant thickening of the wall of the uterus as a preparation for implantation
Why does the cervical mucus get thinner?
To allow passage of sperm
The ovarian cycle:
- Follicular phase > Follicular growth > GDF9
- ovulation > LH surge lead to ovulation > release the oocyte by rupture of follicle
- luteal phase > corpus luteum
Primary oocyte to begin to mature within the……
growing follicles
Corpus luteum develop from….
the remaining of the follicle
The corpus luteum degenerates if
a secondary oocyte is not fertilized
what happens to the remaining follicle after fertilization?
become corpus luteum
what is the role of corpus luteum?
it produces progesterone which is important for the endometrium
what prevents corpus luteum from degenerating?
HCG does not allow it to
degenerate coming from the embryo till the 3 or 4th month till the formation of the placenta
what happens to the corpus luteum if not fertilized?
the corpus luteum die
Why does FSH and LH surge during ovulation?
because we need the supply to change the secondary oocyte into a to a mature follicle. (complete meiosis 1)
who block additional oocyte for differentiation?
AMH
Why do we get the surge of estrogen around the same time of ovulation?
We get the estrogen from the theca interna and granulosa cells
what is LH surge role in the production of progesterone?
It stimulates production of progesterone by follicular stromal cells (leutinization) and
causes follicular rupture and ovulation
Why do we get a surge of progesterone after estrogen (after ovulation)?
Because it’s increases within the luteal phase in which the corpus luteum is the one
responsible for the surge
What is the importance of progesterone?
Important for thickening of the wall of the uterus
How does the oocytes to complete meiosis I and initiate meisosis II?
By the LH surge that elevates concentrations of maturation-promoting factor
What happens when LH has high concentrations? (surge)
- increase collagenase activity
- increase Prostaglandins
- squeeze the oocyte along with its granulosa cells from the region of cumulus oophuru
what happens when we increase collagenase activity?
that will lead to the breakdown of collagen fibers surrounding the follicle.
what happens when we increase prostaglandins?
will cause muscular contractions in the ovarian wall
What happens to the granulosa cells in the wall of the ruptured follicle’s and the theca interna cells?
After ovulation they are vascularized by surrounding vessels
How does the follicular rupture turn into corpus luteum?
Under the influence of LH these cells develop a yellowish pigment and transform into
lutein cells which secrete estrogens and progesterone
What is the importance of estrogen and progesterone secretion?
cause uterine mucose to enter progestational phase in preparation for implantation
(Uterine wall thickening)
How is the oocyte is carried into the uterine tube?
by sweeping motions of the fimbrae and by the cilia on the epithelial lining
what is the role peristaltic muscular contractions in the Oocyte transport?
Once the oocyte in the tube peristaltic muscular contractions with the rate of trasport
regulated by the endocrine status during and after ovulation
What happens to Cumulus cells after Oocyte is transported?
Cumulus cells withdraw their cytoplasmic processes from the zona pellucida and lose
contact with the oocyte.
When doesThe fertilized oocyte reaches the of site fertilization?
in approximately 3 to 4 days
What is the site of fertilization?
The uterine lumen > the ampulla
What happens if fertilization doesn’t occur ?
shrinks to form a mass of fibrotic scar tissue, corpus albicans.
when does the corpus luteum reaches maximum development if not fertilized
approximately 9 days post-ovulation
What do you mean by corpus albicans?
A mass of fibrotic scar tissue formed from the degrading of the corpus luteum.
What happens to progesterone levels when the corpus luteum degrade?
Progesterone production decreases and menstrual bleeding begins
What happens if fertilization occur ?
occurs degeneration of corpus luteum is prevented by human chorionic gonadotropin (hCG) hormone
who secretes HCG
the syncytiotrophoblast (which become the placenta)
What is fertilization?
the process by which male and female gametes fuse and usually occurs in the ampullary region of the uterine tube
What is the percentage of sperm that is deposited ithe vagina enter the cervix ?
• Only 1% of sperm
And for how long does it (the sperm) survive?
survive for many hours
How does sperm Move from the cervix to the uterine tube?
by muscular contractions of the uterus and uterine tube
How long does it take?
from thirty minutes to 3 days
what happen to the Sperm when they reach isthmus?
less motile and cease.
What is Capacitation?
Glycoprotein coat and seminal plasma proteins are removed from the plasms membrane
that overlies the acrosomal region of the spermatozoa
What is the sperm Conditioning period in the female reproductive tract?
lasts around 7 hours
What initiates Capacitation?
Entails epithelial interactions between sperm and mucosal surface of the tube.
Why is Capacitation important?
Because only capactiated sperm can pass through the corona cells (the outsider layer of the zona pellucida) and undergo the acrosome reaction.
When does the acrosomal reaction Occur?
Occurs after binding to the zona pellucida this is induced by zona proteins
What does the acrosomal reaction start with?
Start with the release of enzymes required to penetrate the zona pellucida, including acrosin- and trypsin-like substance
What are the three stages of fertilization?
- Penetration of the corona radiata
- Penetration of the zona pellucida
- Fusion of the oocyte and sperm cell membrane
how many spermatozoa reaches the site of fertilization?
300 to 500 out of 300 million spermatozoa reach the site of fertilization
what is the zona pellucida?
a glycoprotein shell surrounding the egg
what’s the function of zona pellucida?
facilitates sperm
binding and induces the acrosome reaction
the role of the ligand ZP3:
mediated the binding and the acrosome reaction
what does the release of acrosin do?
allows the sperm to penetrate the zona, coming in contact
with the plasms membrane of the oocyte
when does the Fusion of the oocyte and sperm cell membrane
occurs after adhesion in the equatorial segment of the sperm with the oocyte
What changes take place in the oocyte on entering spermatozoa? (From oocyte point of view)
- cortical and zona reactions > prevent the entry of other sperms
- Resumption of second meiotic division
- Metabolic activation of the egg > Fusion and doubling of DNA by mitosis
What are the Results of the fusion of oocyte & sperm?
- Restoration of diploid number of chromosomes
- Sex determination
- Initiation of cleavage
What’s a cleavage?
a series of mitotic divisions, increasing the number of cells
How long does it take for the zygote to reach the two cell stage?
30 hours post-fusion.
When does the zygote start cleavage process ?
Once the zygote has reached the two-cell stage
When do we have blastomeres?
When the two-cell stage zygote become smaller with every dvision.
What’s a morula?
Once the zygote reaches the 8-cell stage they become compact and resemble a mulberry
inner cells of the morula makes up….
the inner cell mass
the surrounding cells of the morula makes up….
the outer cell mass
when is the blastocyst made?
Four days after fertilization the morula moves into the uterus and fluid filled cavity is formed
Where does the Fluid begins to penetrate?
through the zona pellucida into the intercellular spaces of the inner cell mass.
What do we call the cells after the Fluid begins to penetrate through the zona pellucida into the
intercellular spaces of the inner cell mass?
- Cells of the inner cell mass > embryoblast that are at one pole
- Cells of the outer cell mass > the trophoblast flatten
What is formed by the trophoblast flatten?
form the epithelial wall of the blastocyst.
The Uterus undergo several changes during the menstrual cycle in three stages, what are they?
- Follicular phase
- Secretory phase
- Menstrual phase
when does the secretory phase happen?
which Starts 2-3 days after ovulation in response to progesterone
When does the Implantation take place?
in the secretory phase
What are the sides of Implantation?
ideally occurs within the body of the uterus, usually either on the anterior or posterior wall.
Define ectopic pregnancy?
when the blastocyst may implant in an area other than the corpus uteri.
Why is an ectopic pregnancy considered as obstetric emergencies that regrettably require
termination?
they threaten the life of the mother and the implantation site cannot facilitate the projected fetal growth.
What are the most common ectopic pregnancies?
Tubal ectopic pregnancies which occur Within the fallopian tubes.
What are the most common sites of Tubal ectopic pregnancy ?
is most likely to happen in the
ampulla > then at isthmus > followed by the infundibulum
