lOMoARcPSD|26582732
The Menstrual Cycle, Premenstrual Conditions, and Abnormal
2025
1. Be able to explain the approximate timing and symptoms of menarche, the
menstrual cycle, and menopause. The menstrual cycle physiology
● Initiation of menstruation = menarche @ 12 and 15 yrs old and continues until age 45-
55 when menopause occurs
● The ratio of total body weight to lean body weight is probably the most relevant factor,
and individuals who are moderately obese (i.e., 20–30 percent above their ideal body
weight) tend to have an earlier onset of menarche
2. How does the HPO axis regulate the menstrual cycle?
The hypothalamic-pituitary-ovarian axis Hypothalamus
● Controls anterior pituitary function via the secretion of releasing and inhibiting factors;
manages the production of hormones that serve as chemical messengers for the
regulation of the gynecologic system
● Hypothalamus release gonadotropin-releasing hormone (gnrh) in a pulsatile manner;
gnrh secretion released during the follicular phase, increase in menstrual cycle then
decrease during the luteal phase
● The release of gnrh stimulates the pituitary gland to produce follicle-stimulating
hormone (FSH) and luteinizing hormone (LH) which stimulates the release of estrogen
and progesterone Pituitary gland
● Oval-shaped, pea-sized pituitary gland located in a small depression in the sphenoid
bone of the skull controlled by the hypothalamus that secretes factors into special blood
vessel network that feeds the pituicytes
● Anterior pituitary synthesize seven hormones: growth hormone (GH),
Thyroid-stimulating hormone (TSH), Adrenocorticotropin (ACTH),
Melanocyte-stimulating hormone (MSH), Prolactin (PRL), Follicle-stimulating hormone
(FSH), Luteinizing hormone (LH)
● FSH and LH = gonadotropins
● FSH targets the ovaries and stimulates the growth of primary follicles that resulting in
estrogen and progesterone production
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, lOMoARcPSD|26582732
● FSH governed by a negative feedback mechanism involves steroid
● LH target the developing follicle within the ovary, responsible for ovulation, corpus
luteum formation and hormone production in the ovaries
Ovaries and Uterus
● Ovarian cycle goal is to produce an ovum and endometrial cycle goal is to prepare a site
to nourish and maintain the ovum if it becomes fertilized
● Ovarian cycle: follicular phase, ovulation and luteal phase
● Endometrial cycle: proliferative phase, secretory phase and menstruation
Hormonal Feedback System
● Monthly rhythmic function of the menstrual cycle depends on the changing
concentration of gonadotropic hormones
● LH and FSH important in stimulating estrogen and progesterone; LH and FSH depends on
the gnrh from the hypothalamus
● Under normal conditions, gnrh pulses stimulate the release of FSH and LH causing the
gonadotropic hormone stimulation, the ovarian follicle develop and produce estrogen
● As the amount of estrogen in the system increases and reach the pituitary gland, it
affects the amount of FSH and LH secreted (negative feedback)
● When estrogen level become high enough, the negative feedback effect on the pituitary
is reversed
○ Estrogen cause mid cycle positive feedback on the pituitary which cause LH and
FSH surge = ovulation
○ LH cause the rupture of follicle = corpus luteum = secretes progesterone that
sustain the corpus luteum
○ No pregnancy = corpus luteum degenerates = progesterone level decrease =
menstruation and gnrh pulses return to the frequency associated with the
beginning of the follicular phase and a new cycle begin
3. Explain what occurs during each phase of the ovarian cycle and during each phase
of the endometrial cycle.
Ovarian cycle: follicular, ovulatory and luteal
Follicular phase: development of ovarian follicles and last from day 1 (first day of menses) to
day 14 of the ovarian cycle
● Folliculogenesis begins the last few days of the previous menstrual cycle and continue
until the release of mature follicle at ovulation
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, lOMoARcPSD|26582732
● Decrease in estrogen production by the corpus luteum and dramatic fall of inhibin level
allow FSH level to rise during the last few days of menstrual cycle
● Day 1-4 of menstrual cycle, primary follicles are recruited from a pool of
nonproliferating follicles in response to the increased concentration of FSH
○ The primary role of FSH = induce the development of increased receptors on the
granulosa cells = estrogen production
○ The primary role of LH = stimulate cells’ production of androgen that will be
converted to estrogen by granulosa layers
● Cycle day 5-7, only one dominant follicle from the cohort of recruited follicles is
destined to ovulate during the next menstrual cycle
○ Menses progress, FSH level decline due to the negative feedback of estrogen
and negative effects on the peptide hormone inhibin = follicle develop
● 8th day, the dominant follicle (graafian follicle) produces more estrogen than the total
amount produced by other developing follicles
○ LH receptor flourish and move to the ovary’s surface
○ Oocyte maturation inhibitor (OMI) in the follicular fluid suppresses the final
maturation of the dominant follicle until the time of ovulation Ovulatory phase
● Ovulation = mature ovum release from the follicle
● Ovulation and the conversion of follicle to corpus luteum are dependent on an
increased level of estrogen and LH surge which marks the beginning of a rapid rise of LH
● Mid Follicular phase, dominant follicle’s FSH levels diminish but estrogen levels continue
to increase
● High estrogen level initiates a positive feedback of LH, generating the preovulatory LH
surge
● Oocyte breaks down, chromosome progress through the meiotic division and egg move
on to the secondary stage; meiosis cease and will be initiated again only if the ovum is
fertilized Luteal Phase
● Under the influence of LH, the follicle’s granulosa cells that are left in the ruptured
follicle become enlarged, undergo luteinization, and form the corpus luteum; it secretes
increased progesterone and some estrogen that start the negative feedback loop to the
hypothalamus and pituitary gland, preventing further ovulation within the current cycle
Downloaded by NELSON KIIRU ()
, lOMoARcPSD|26582732
● No fertilized ovum = luteal cell degenerates = decline estrogen and progesterone level =
corpus luteum regress to become corpus albicans = estrogen and progesterone
decrease = remove the negative feedback effect
● FSH and LH increase once again to initiate the next menstrual cycle
Endometrial cycle: proliferative, secretory and menstrual
Proliferative Phase: estrogen and regrowth of endometrium after the menstrual bleed ●
involves changes in the endometrium, myometrium, and ovaries.
● Fluctuations in gonadotropin and estrogen levels, are characterized by progressive
mitotic growth of the decidua functional in response to increasing levels of estrogen
secreted by the ovary; preparation for implantation of the fertilized ovum
● Begin of the proliferative phase, the endometrium is thin and endometrial glands are
straight, narrow and short
● As the phase progresses, the gland becomes long and tortuous. Endometrium becomes
thicker from the glandular hyperplasia and growth of the stroma
● The endometrium proliferates from 4 to 12 mm in height and increase eightfold in
thickness in preparation for implantation of the fertilized ovum Secretory phase: begins
at ovulation
● Gland of the endometrium become more tortuous and dilated and fill with secretion,
primarily as a result of increased progesterone production
● Endometrium becomes thick, cushiony and nutritive in preparation for implantation of
fertilized ovum
● No implantation, corpus luteum shrink, and progesterone and estrogen level decrease
● Endometrium regress toward secretory phase
● P rogesterone and estrogen withdrawal results in increased tortuous coiling and
constriction of the spiral arterioles in the thinning layer
Menstrual phase: begin with the initiation of menses and last 3-5 days
● Enzymatic autodigestion of the functional layer of the endometrium
● The degradation of the endometrium is progressive and causes interstitial hemorrhage
whereby dissolution of the surface membrane allows blood to escape into the
endometrial cavity
3. How do hormonal changes affect the cervix, fallopian tube mobility, and vagina?
Downloaded by NELSON KIIRU ()
The Menstrual Cycle, Premenstrual Conditions, and Abnormal
2025
1. Be able to explain the approximate timing and symptoms of menarche, the
menstrual cycle, and menopause. The menstrual cycle physiology
● Initiation of menstruation = menarche @ 12 and 15 yrs old and continues until age 45-
55 when menopause occurs
● The ratio of total body weight to lean body weight is probably the most relevant factor,
and individuals who are moderately obese (i.e., 20–30 percent above their ideal body
weight) tend to have an earlier onset of menarche
2. How does the HPO axis regulate the menstrual cycle?
The hypothalamic-pituitary-ovarian axis Hypothalamus
● Controls anterior pituitary function via the secretion of releasing and inhibiting factors;
manages the production of hormones that serve as chemical messengers for the
regulation of the gynecologic system
● Hypothalamus release gonadotropin-releasing hormone (gnrh) in a pulsatile manner;
gnrh secretion released during the follicular phase, increase in menstrual cycle then
decrease during the luteal phase
● The release of gnrh stimulates the pituitary gland to produce follicle-stimulating
hormone (FSH) and luteinizing hormone (LH) which stimulates the release of estrogen
and progesterone Pituitary gland
● Oval-shaped, pea-sized pituitary gland located in a small depression in the sphenoid
bone of the skull controlled by the hypothalamus that secretes factors into special blood
vessel network that feeds the pituicytes
● Anterior pituitary synthesize seven hormones: growth hormone (GH),
Thyroid-stimulating hormone (TSH), Adrenocorticotropin (ACTH),
Melanocyte-stimulating hormone (MSH), Prolactin (PRL), Follicle-stimulating hormone
(FSH), Luteinizing hormone (LH)
● FSH and LH = gonadotropins
● FSH targets the ovaries and stimulates the growth of primary follicles that resulting in
estrogen and progesterone production
Downloaded by NELSON KIIRU ()
, lOMoARcPSD|26582732
● FSH governed by a negative feedback mechanism involves steroid
● LH target the developing follicle within the ovary, responsible for ovulation, corpus
luteum formation and hormone production in the ovaries
Ovaries and Uterus
● Ovarian cycle goal is to produce an ovum and endometrial cycle goal is to prepare a site
to nourish and maintain the ovum if it becomes fertilized
● Ovarian cycle: follicular phase, ovulation and luteal phase
● Endometrial cycle: proliferative phase, secretory phase and menstruation
Hormonal Feedback System
● Monthly rhythmic function of the menstrual cycle depends on the changing
concentration of gonadotropic hormones
● LH and FSH important in stimulating estrogen and progesterone; LH and FSH depends on
the gnrh from the hypothalamus
● Under normal conditions, gnrh pulses stimulate the release of FSH and LH causing the
gonadotropic hormone stimulation, the ovarian follicle develop and produce estrogen
● As the amount of estrogen in the system increases and reach the pituitary gland, it
affects the amount of FSH and LH secreted (negative feedback)
● When estrogen level become high enough, the negative feedback effect on the pituitary
is reversed
○ Estrogen cause mid cycle positive feedback on the pituitary which cause LH and
FSH surge = ovulation
○ LH cause the rupture of follicle = corpus luteum = secretes progesterone that
sustain the corpus luteum
○ No pregnancy = corpus luteum degenerates = progesterone level decrease =
menstruation and gnrh pulses return to the frequency associated with the
beginning of the follicular phase and a new cycle begin
3. Explain what occurs during each phase of the ovarian cycle and during each phase
of the endometrial cycle.
Ovarian cycle: follicular, ovulatory and luteal
Follicular phase: development of ovarian follicles and last from day 1 (first day of menses) to
day 14 of the ovarian cycle
● Folliculogenesis begins the last few days of the previous menstrual cycle and continue
until the release of mature follicle at ovulation
Downloaded by NELSON KIIRU ()
, lOMoARcPSD|26582732
● Decrease in estrogen production by the corpus luteum and dramatic fall of inhibin level
allow FSH level to rise during the last few days of menstrual cycle
● Day 1-4 of menstrual cycle, primary follicles are recruited from a pool of
nonproliferating follicles in response to the increased concentration of FSH
○ The primary role of FSH = induce the development of increased receptors on the
granulosa cells = estrogen production
○ The primary role of LH = stimulate cells’ production of androgen that will be
converted to estrogen by granulosa layers
● Cycle day 5-7, only one dominant follicle from the cohort of recruited follicles is
destined to ovulate during the next menstrual cycle
○ Menses progress, FSH level decline due to the negative feedback of estrogen
and negative effects on the peptide hormone inhibin = follicle develop
● 8th day, the dominant follicle (graafian follicle) produces more estrogen than the total
amount produced by other developing follicles
○ LH receptor flourish and move to the ovary’s surface
○ Oocyte maturation inhibitor (OMI) in the follicular fluid suppresses the final
maturation of the dominant follicle until the time of ovulation Ovulatory phase
● Ovulation = mature ovum release from the follicle
● Ovulation and the conversion of follicle to corpus luteum are dependent on an
increased level of estrogen and LH surge which marks the beginning of a rapid rise of LH
● Mid Follicular phase, dominant follicle’s FSH levels diminish but estrogen levels continue
to increase
● High estrogen level initiates a positive feedback of LH, generating the preovulatory LH
surge
● Oocyte breaks down, chromosome progress through the meiotic division and egg move
on to the secondary stage; meiosis cease and will be initiated again only if the ovum is
fertilized Luteal Phase
● Under the influence of LH, the follicle’s granulosa cells that are left in the ruptured
follicle become enlarged, undergo luteinization, and form the corpus luteum; it secretes
increased progesterone and some estrogen that start the negative feedback loop to the
hypothalamus and pituitary gland, preventing further ovulation within the current cycle
Downloaded by NELSON KIIRU ()
, lOMoARcPSD|26582732
● No fertilized ovum = luteal cell degenerates = decline estrogen and progesterone level =
corpus luteum regress to become corpus albicans = estrogen and progesterone
decrease = remove the negative feedback effect
● FSH and LH increase once again to initiate the next menstrual cycle
Endometrial cycle: proliferative, secretory and menstrual
Proliferative Phase: estrogen and regrowth of endometrium after the menstrual bleed ●
involves changes in the endometrium, myometrium, and ovaries.
● Fluctuations in gonadotropin and estrogen levels, are characterized by progressive
mitotic growth of the decidua functional in response to increasing levels of estrogen
secreted by the ovary; preparation for implantation of the fertilized ovum
● Begin of the proliferative phase, the endometrium is thin and endometrial glands are
straight, narrow and short
● As the phase progresses, the gland becomes long and tortuous. Endometrium becomes
thicker from the glandular hyperplasia and growth of the stroma
● The endometrium proliferates from 4 to 12 mm in height and increase eightfold in
thickness in preparation for implantation of the fertilized ovum Secretory phase: begins
at ovulation
● Gland of the endometrium become more tortuous and dilated and fill with secretion,
primarily as a result of increased progesterone production
● Endometrium becomes thick, cushiony and nutritive in preparation for implantation of
fertilized ovum
● No implantation, corpus luteum shrink, and progesterone and estrogen level decrease
● Endometrium regress toward secretory phase
● P rogesterone and estrogen withdrawal results in increased tortuous coiling and
constriction of the spiral arterioles in the thinning layer
Menstrual phase: begin with the initiation of menses and last 3-5 days
● Enzymatic autodigestion of the functional layer of the endometrium
● The degradation of the endometrium is progressive and causes interstitial hemorrhage
whereby dissolution of the surface membrane allows blood to escape into the
endometrial cavity
3. How do hormonal changes affect the cervix, fallopian tube mobility, and vagina?
Downloaded by NELSON KIIRU ()
