Menstrual Cycle and Ovulation Flashcards
the menstrual cycle can be broken down into 2 different cycles. What are they?
ovarian cycle and the endometrial cycle
what are the phases of the ovarian cycles?
follicular phase and the luteal phase
what are the phases of the endometrial phase?
menses, proliferative phase, and secretory phase
what is the primary hormone involved in the follicular phase?
estrogen
what is the primary hormone involved in the luteal phase?
progesterone
what stage of meiosis are the primordial germ cells in arrest at?
prophase I
what keeps the primordial germ cells in meiotic arrest?
elevated levels of cAMP
how long do the primordial germ cells stay in meiotic arrest in prophase I?
until the LH surge
where does the second meiotic arrest occur?
metaphase II
how does the second meiotic arrest in metaphase II occur?
elevated levels of MAPK proteins
when is there resumption of meiosis II?
only at fertilization
what is the functional unit of the ovary?
ovarian follicle
what happens in the follicle of the ovary?
gametes develop and mature
what is the primordial follicle surrounded by?
a single layer of pregranulosa cells
what does the primordial follicle represent?
the ovarian reserve
within the primordial follicle what type of oocyte would you find?
primary oocyte
what is the primary follicle surrounded by?
a single layer of granulosa cells- cuboidal shape
Besides the shape of the granulosa cells surrounding the primary follicle, what is another key feature of the primary follicle?
there is early production of secreted glycoprotein (ZP1-4)
within the primary follicle what type of oocyte would you find?
primary oocyte
what is the secondary follicle surrounded by?
3-6 layers of cuboidal granulosa cells
besides the multiple layers of granulosa cells surrounding the secondary follicle, what is another key feature of the secondary follicle?
there are now secretions of paracrine factors to induce local stromal cells to differentiate into thecal cells
the progression to a secondary follicle involves increased what?
vascularization
what do the secondary follicles release to increase vascularization?
angiogenic factors- induce the development of 1-2 arterioles
what does the induction of the development of 1-2 arterioles generate?
a vascular wreath
what are the preantral follicles dependent on for oocyte growth?
paracrine factors (the granulosa cells express FSH receptors)
when does the antrum begin developing?
during the secondary follicle stage
what is the term for when the oocyte is suspended in fluid surrounded by a dense mass of granulosa cells?
cumulus oophorus
what happens during the antral phase of follicular development?
there is a 100-fold increase in granulosa cells
what are the two distinct populations of granulosa cells that appear during the antral phase?
mural granulosa (stratum granulosum) and cumulus cells
when does growth of the follicle become responsive to gonadotropins?
at the antral follicle stage (late secondary stage)
what happens when LH interacts with its receptors on the theca interna cells?
they synthesize androgens
what do theca interna cells synthesize the androgens from?
acetate and cholesterol
what happens when the granulosa cells interact with FSH?
they will convert the androgens that are produced by the theca cells into estrogen
what is the reaction that converts androgens into estrogen?
aromatization
when does the oocyte become competent to complete meiosis I at ovulation?
at the antral stage
what do the mural granulosa cells produce?
low levels of estrogen and inhibin B
midcycle, what does the dominant follicle become?
a large preovulatory follicle (graffian follicle)
what is the periovulatory period?
the time from onset of the LH surge to ovulation (32-36 hours)
what occurs during the periovulatory period?
structural changes and changes in the steroidogenic function of the theca and mural granulosa
what does the LH surge induce?
differentiation (luteinization) of granulosa cells to granulosa lutein cells
what do the granulosa cells express at the time of the LH surge?
LH receptors
during the luteinization, what are the granulosa cells inhibiting?
aromatase expression
what does less aromatase expression result in?
a rapid decline in the androgens being converted into estradiol; this rapid decline reduces positive feedback on LH secretion
what effect does the increased vascularization have on the granulosa cells during luteinization?
it increases the cholesterol availability for progesterone production
How does the follicle wall, tunica albuginea, and surface epithelium breakdown?
through the release of cytokines and hydrolytic enzymes from theca and granulosa cells
what is the antral cavity filled with during the luteal phase? and what is it called now (the transient stage between the follicle and the corpus luteum)
blood/ cell debris- called the corpus hemorrhagicum
once the corpus hemorrhagicum is removed by macrophages, what is the antral cavity filled with?
granulosa lutein cells, cholesterol esters, theca cells, blood vessels, and white blood cells
how long does the corpus luteum remain?
around 2 weeks
what is the scar-like body that develops from the corpus luteum and what is it primarily composed of?
corpus albicans- primarily collagen
what is the corpus luteum sensitive to?
HCG (similar in structure to LH)
what happens if fertilization happens and the trophoblast begins secreting hCG?
the corpus luteum will continue producing progesterone
what is the role of the progesterone produced by the corpus luteum during pregnancy?
it transforms the uterine lining into an adhesive and supportive structure
why is the reduction of LH and secretion of inhibin by lutein cells (suppression of FSH) important if there is pregnancy?
it prevents the production of other follicles if there is pregnancy (so that there is not additional energy going into follicular development during pregnancy)
how does atresia occur?
apoptosis (due to the decline of FSH)
what happens to the thecal cells of follicles that have been apoptosed?
thecal cells persist and repopulate the cellular stroma of the ovary (known as the interstitial gland of the ovary)
what do LH and FSH stimulate the ovary to do?
synthesize and secrete estrogens and progestins
early in the follicular phase, what is the sensitivity like of the gonadotrophs to GnRH?
early in the follicular phase, gonadotrphs are not very GnRH sensitive; each burst of GnRH elicits only a small rise in LH
later in the follicular phase, what is the sensitivity like of the gonadotrphs to GnRH?
later in the follicular phase, gonadotrophs in the anterior pituitary become much more sensitive to GnRH in the portal blood; each burst of GnRH triggers a much larger release of LH
what enhances the sensitivity of the gonadotrophs to GnRH?
the high levels of estradiol that are typical of the late follicular phase
theca cells have what type of receptors?
LH receptors
granulosa cells have what type of receptors?
both LH and FSH
what is required for estrogen production?
both LH and FSH are required
after ovulation, what does LH act on?
the cells of the corpus luteum
what is inhibin produced by in females?
the granulosa cells of the follicle
what stimulates the granulosa cells to produce inhibins?
FSH; just before ovulation, after the granulosa cells acquire LH receptors, LH stimulates the production of inhibin by granuosa cells
what is the action of inhibins in females?
it inhibits FSH production by gonadotrophs (this negative feedback loop is really necessary for selecting that dominate follicle)
what is the role of activins?
they are produced in the same tissues as the inhibins but they stimulate FSH release from the pituitary cells
what is the net effect of the estrogens and progestins feeding back to the hypothalamus and the pituitary>
to reduce LH and FSH release
after the estradiol levels reach a certain threshold what happens to the HP axis?
it reverses its sensitivity to estrogens, it now exerts a positive feedback–> promotes the LH surge
what is involved in the induction of the LH surge?
positive feedback of estrogens, progestins, and activins on the HP axis
what happens to the LH and FSH levels as the luteal phase of the menstrual cycle begins?
they rapidly decrease
what does the fall off of gonadotropin levels as the luteal phase of the menstrual cycle begins reflect?
negative feedback by estradiol, progesterone, and inhibin
during the luteal phase, the rise in concentration of estradiol, progesterone, and inhibin causes what?
the continued decrease of gonadotropin levels midway through the luteal phase
during the late luteal phase, the gradual demise of the corpus luteum leads to what?
decreases in the levels of progesterone, estradiol, and inhibin
during the follicular phase, what is the major product of the follicle?
estradiol
during the luteal phase, what are the major products of the corpus luteum?
progestins, although estradiol synthesis is still substantial
what effect on the basal body temperature do the higher levels of estrogen present during the pre-ovulatory (follicular) phase of the menstrual cycle have?
they lower BBT
what effect does the higher levels of progesterone released by the corpus luteum after ovulation have on basal body temperature?
they raise BBT
when can the rise in BBT most commonly be seen?
the day after ovulation
if the oocyte was not fertilized and pregnancy did not occur in the previous cycle, what causes the demise of the corpus luteum?
a sudden diminution in estrogen and progesterone secretion
what is the proliferation and differentiation of the endometrium during the proliferative phase stimulated by?
estrogen (which is secreted by the developing follicles)
what causes the induction of the synthesis of progestin receptors in the endometrial tissue?
estrogen
what promotes the differentiation of the stromal cells into predecidual cells?
progesterone
when is the average age of menopause?
51.4 years of age
what is menopause caused by?
there is a reduction in estrogen, so there are low levels of inhibin; there is no negative feedback of LH and FSH, therefore there are high levels of LH and FSH seen with menopause
