Chapter 27: Reproductive System: Part IV: Female Reproductive System - Menstrual Cycle
What are the phases of the ovarian cycle?
A. Ovarian Cycle: -Follicular phase -Ovulation (separates phases) -Luteal phase
What is the ovarian cycle? What is the uterine cycle?
A. Ovarian Cycle: monthly series of events associated with maturation of an egg (follows follicle through 28 day menstrual cycle) -Follicular phase (corresponds to period of time when a cohort of vesicular follicles are beginning to secrete estrogen and one of those follicles is selected as the dominant follicle) -Ovulation (follicular phase ends with ovulation) (dominant follicle ejects its secondary oocyte in the corona radiata at ovulation) -Luteal phase (the period of time in which the corpus luteum is active and its secreting estrogens and progesterone) B. Uterine Cycle: series of cyclic changes that the uterine endometrium goes through each month as it responds to changing levels of ovarian hormones in the blood -Menstrual phase (when the endometrium is shedding) -Proliferative phase (when the endometrium is being rebuilt) -Secretory phase (when the endometrium is preparing for implantation)
What are the phases of the uterine cycle?
B. Uterine Cycle: -Menstrual phase (endometrium shedding) -Proliferative phase (endometrium regenerating) -Secretory phase (endometrium preparing for embryo to implant)
Describe the series of events, if fertilization does occur, that prevent menses.
-If fertilization occurs: //Blastocyst (embryo) implants (in endometrial wall): //Trophoblast cells release the hormone hCG (human chorionic gonadotropin) // hCG acts like LH to stimulate corpus luteum (act like survival factor to keep corpus luteum alive) //(hCG is the hormone detected by pregnancy test) -Corpus luteum does NOT degenerate (when hCG is present) and continues to release estrogen and progesterone which maintain endometrium -Corpus luteum continues for about 3 months -Placenta takes over secretion of estrogen and progesterone
Describe the series of events, if no fertilization occurs, that lead to menses.
-If no fertilization: //Declining LH levels cause corpus luteum to degenerate //With degenerating corpus luteum, estrogen and progesterone levels fall //With falling estrogen and progesterone levels, endometrium is NOT maintained --> menses (stratum functionalis detaches) -Also with drop in estrogen and progesterone, FSH and LH levels start to rise (recruits another cohort of follicles to begin growing and maturing and cycle repeats) -Cycle repeats
What are the 6 steps regarding Hormonal Control of Menstrual Cycle?
1. GnRH (released from hypothalamus) (acts at anterior pituitary) and stimulates LH and FSH secretion 2. FSH and LH stimulate follicles to grow, mature, and secrete sex hormones 3. Negative feedback inhibits gonadotropin release 4. Positive feedback stimulates gonadotropin release 5. LH surge triggers ovulation and formation of corpus luteum 6. Negative feedback inhibits release of FSH and LH
In menses describe what is happening to the levels of GnRH, LH and FSH. Step 2 What does LH do during this period? What does FSH do doing this period? What steroid hormone increases as a result?
FSH and LH stimulate follicles to grow, mature, and secrete sex hormones -FSH recruits group of follicles (in ovaries) to grow and mature (and start secreting sex hormone) -LH stimulates theca folliculi --> androgens -FSH stimulates granulosa cells --> convert androgens to estrogens -Estrogen levels start to rise (stimulus for)(proliferative phase in uterine) (cycle) (causes stratum basalis to regenerate stratum functionalis)(As estrogen levels start to rise that corresponds to that group of vesicular follicles growing and maturing, LH hormones stimulating theca folliculi, and FSh stimulating granulosa cells)
What are the phases of the ovarian cycle and what happens in each phase? Follicular phase
Follicular Phase -Cohort of (vesicular) follicles were selected to grow (and mature) //Follicle stimulating hormone (FSH) is survival factor (FSH is stimulus for them to grow and mature) //Cohort of vesicular follicles begins secreting increasing amounts of estrogens (as they are growing and maturing) -(just prior to ovulation) One follicle is selected as dominant vesicular follicle; completes meiosis I to form secondary oocyte and first polar body -Lasts from day 1-14 of ovarian cycle (when ovulation is going to occur) (in a typical 28 day cycle, anytime not 28 days its bc follicular phase is less than or greater that 14 days)
In menses describe what is happening to the levels of GnRH, LH and FSH. Step 1
GnRH stimulates FSH and LH secretion -Day 1 (menses): GnRH (released from hypothalamus) --> FSH & LH released
What happens if fertilization does not occur?
If fertilization does not occur... -Corpus luteum degenerates toward end of secretory phase -(if you take progesterone away) Endometrium becomes deprived of hormonal support -(this causes) Spiral arteries go into spasms -Endometrial cells and glands are deprived of oxygen and nutrients -Spiral arteries fragment -(Degenerates around day 10 of luteal phase)
What happens if fertilization does occur?
If fertilization does occur... -Corpus luteum does persists until month 3 (continues producing hormones) -Hormonal support remains high -Endometrium prepares for implantation and does not get sloughed off
In menses describe what is happening to the levels of GnRH, LH and FSH. Step 5 In the late proliferative phase there is a surge in LH from the pituitary. Explain what causes it. Describe what the surge in LH causes.
LH surge triggers ovulation and formation of corpus luteum -(high estrogen levels elicited positive feedback mechanism which caused) Sudden burst of LH LH stimulates primary oocyte of mature vesicular follicle to complete meiosis I, begin meiosis II, and arrest in metaphase II -LH causes mature vesicular follicle to rupture -Oocyte and corona radiata are ejected -Estrogen levels drop (due to ruptured follicle) -LH stimulates ruptured follicle to become corpus luteum
What are the phases of the ovarian cycle and what happens in each phase? Luteal phase
Luteal Phase -Remaining granulosa cells (as well as theca foliculi) form corpus luteum which secretes progesterone and estrogens //Pregnancy occurs: corpus luteum persists for 3 months until placenta forms //Pregnancy does NOT occur: corpus luteum degenerates 10 days later and stops producing hormones -Last 2-3 days of luteal phase, (corpus luteum degenerates and) endometrium begins to erode: ischemic or luteolytic phase -Days 14-28; always 14 days from ovulation to end of cycle (always constant) -(Variation in menstrual cycle doesn't come from variation in luteal phase length, it comes from variation in the length of the follicular phase)
What are the phases of the uterine cycle and what happens in each phase? Time-wise, how are the phases of each related? Menstrual phase
Menstrual Phase -(also called) Menstruation or menses -Uterus sheds all but deepest part of endometrium -Stratum functionalis detaches (but stratum basalis persists) -Corresponds with early follicular phase of ovarian cycle (cohort of follicles is being recruited to grow) -(About day 1-5 of menstrual cycle)
Describe what is happening to the levels of the following hormones during the luteal stage: LH, FSH, estrogen, progesterone.
Negative feedback inhibits LH and FSH release -Luteal phase: //Newly formed corpus luteum (Granulosa cells from ruptured follicle has been converted into croups luteum) secretes both Estrogen and Progesterone //Hormones (progesterone specifically) cause the secretory stage in uterus (which is preparing for implantation to occur)(causes uterine glands to enlarge and spiral network arteries to become elaborate) //High levels of estrogen and progesterone (and inhibin) have a negative feedback on LH & FSH //Inhibits maturation of additional follicles for ovulation (prior to the end of the menstrual cycle)
In menses describe what is happening to the levels of GnRH, LH and FSH. Step 3 During the early proliferative phase, name the 2 hormones inhibiting FSH and LH. The decrease in FSH and LH levels have what effect on the ovary?
Negative feedback inhibits gonadotropin release -High estrogen levels (of growing and maturing follicles)(negatively) feedback and inhibit release of FSH -(granulosa cells of growing and maturing follicles produce) Inhibin, released by granulosa cells, also inhibits FSH release -Result: dip in FSH, only one vesicular follicle survives and others undergo apoptosis (programmed cell death)
What happens from the onset of puberty?
Onset of puberty -Ovaries grow and secrete small amounts of estrogens that inhibit hypothalamic release of GnRH -Eventually, body levels of adipose tissue and fatty tissue hormone leptin RISE and allow hypothalamus to release GnRH //Onset of puberty (linked to amount of adipose tissue and fatty tissue hormone leptin) -(GnRH) Stimulates anterior pituitary to release gonadotropins (FSH and LH) -(this then begins the) Menarche or first menstruation -(Leptin can override estrogens negative feedback mechanism and can stimulate the hypothalamus to release GnRH, when GnRH is released from hypothalamus this is considered the onset of puberty)
Describe the effects of estrogen and progesterone which are separate from their effects on the ovary and endometrium.
Other effects of female hormones -Estrogen: //Anabolic effect on reproductive tract (causes many reproductive tract organs to start enlarging making them more function and ready for pregnancy) //Growth spurt of adolescence //Bone growth and maintenance -Female secondary sex characteristics //Breasts //Subcutaneous fat //Widening of pelvis (adaptation for child birth) -Progesterone: //Works with estrogen to stimulate mammary gland development during pregnancy //Pregnancy: calms uterus (inhibits uterine motility prior to labor)
What are the phases of the ovarian cycle and what happens in each phase? Ovulation
Ovulation -Mature (dominant) vesicular follicle and surrounding ovary wall rupture and released secondary oocyte and corona radiata into peritoneal cavity -(occurs on) Day 14 (in typical 28 day cycle)
In menses describe what is happening to the levels of GnRH, LH and FSH. Step 4
Positive feedback stimulates gonadotropin release -Dominant vesicular follicle matures and just before ovulation begins secreting high levels of estrogens -Estrogen now positively feeds back and stimulates gonadotropin release -(Estrogen elicits negative feedback mechanism during early to mid follicular phase when it comes from the group of growing and maturing follicles but estrogen elicits positive feedback mechanism when high estrogen levels being released from dominant vesicular follicle just prior to ovulation so in late follicular phase)
What are the phases of the uterine cycle and what happens in each phase? Time-wise, how are the phases of each related? Proliferative phase
Proliferative Phase -Stratum basalis generates new functional layer in response to rising estrogen levels -Corresponds to later follicular phase of ovary -(uterine) Glands enlarge, spiral arteries increase in # (in the endometrium) Ovulation -Ovulation occurs at end of proliferative phase (day 14) -Cervical mucus is thinned (become less viscous) to facilitate sperm passage (cervical mucous is produced by uterine glands in endometrium)
What are the phases of the uterine cycle and what happens in each phase? Time-wise, how are the phases of each related? Secretory phase
Secretory Phase -14-day phase; constant -Endometrium prepares for embryo to implant -(progesterone produced by corpus luteum stimulates stratum functionalis to have) Uterine glands enlarge and (generate) more elaborate spiral arteries network --> functional layer (stratum functionalis) becomes secretory mucosa (secratory mucosa is highly vascularized so high nutrient and oxygen delivery to an implanted embryo) //Cervical plug (enlarged uterine glands produce this viscous mucous called cervical plug which blocks entry of sperm, pathogens, or other foreign material into female reproductive tract) -Corresponds to luteal phase (which also begins at ovulation and ends 14 days later) -(Stimulus for secretary phase is progesterone that's produced by the corpus luteum in the luteal phase of the ovarian cycle)
Hormone levels figure
Study this figure and know where hormone levels are at during the follicular phase vs luteal phase both for gonadotropins and ovarian hormones and what's going on in ovarian cycle vs uterine cycle Line up when each of these events are happening Study for next exam+++
