principle events of the ovarian and uterine cycles
Hormonal Regulation: GnRH Gonadotropin-releasing hormone (GnRH)
- hypothalamus-controls ovarian and uterine cycles -GnRH stimulates release of FSH and LH -anterior pituitary.
Events in the uterus
-Estrogen liberated in blood by growing follicles stimulates repair of endometrium. -cells in stratum basalis undergo mitosis> produce new stratum functionalis. -Endometrium thickens, -straight endometrial glands develop, -arterioles coil and lengthen, -penetrate stratum functionalis, -thickness doubles.
Events in the uterus
-Menstrual flow: 50-150mL of blood, tissue fluid, mucus, and epithelial cells shed from edometrium. -occurs because of DECLINING LEVELS OF PROGESTERONE AND ESTROGENS: -stimulate release of PROSTAGLANDINS, -cause uterine spiral arterioles to constrict, -cells they supply become O2 deprived, -and die, -stratum unctionalis sloughs off, -endometrium is then very thin, -only stratum basalis remains,
When declining levels of estrogens and progesterones stimulate secretion f GnRH, is this a positive of a negative feedback? Why?
-Negative. -Response is opposite to stimulus. -Reduced amount of negative feedback due to declining levels of estrogens and progesterone stimulate release of GnRH, which in turn increase prodution and release of FSH and LH, ultimately stimulation secretion of estrogens
Female reproductive cycle
-Preovulatory phase is more variable in length than other phases
Events in the uterus
-Progesterone and Estrogens, -produced by corpus luteum, -promote growth and coiling of endometrial glands, -vascularization, and thickening of endometrium. secretory activity of endometrial glands (secrete glycogen), -this period is called the SECRETORY PHASE of the uterine cycle. -preparatory changes peak about 1 week after ovulation., at the time a fertilized ovum might arrive in the uterus -If fertilization does NOT occur: levels of progesterone and esetrogen decline due to degeneration of corpus luteum. Causes menstruation .
Which hormones are responsible for the proliferative phase of endometrial growth, for ovulation, for growth of corpus luteum, and for the surge of LH at midcycle?
-Proliferative phase= Estrogens. -Ovulation= LH. -Growth of corpus luteum-LH. -Midcycle surge of LH- Estrogens.
With reference to the uterine cycle, the preovulatoy phase is also termed the PROLIFERATIVE PHASE
-because endometrium is proliferating.
With reference to the ovarian cycle, the menstrual and preovulatory phases together are termed the FOLLICULAR PHASE
-because ovarian follicles are growing and developing.
Uterine (mentrual) Cycle
-concurrent series of changes in endometrium of the uterus to prepare for the arrival of a fertilized ovum that will develop there until birth. If fertilization doesnt occur: -Ovarian hormones wane, -stratum functionalis of endometrium sloughs off.
Event in one ovary: -If oocyte is NOT fertilized:
-corpus luteum has a life span of only 2 weeks, -secretory activity declines, -degenerates into a corpus albicans. -progesterone, estrogens, and inhibin decrease, -release of GnRH, FSH, and LH rise (loss of negative feedback suppression by ovarian hormones), -follicular growth resumes, -new cycle begins.
Event in one ovary: -If secondary oocyte IS Fertilized and begins to divide:
-corpus luteum persists past its normal 2 week lifespan, -its "rescued" from degeneration by hCG( human chorionic gonadotropin). -produced by chorion of embryo beginning about 8 days after fertilization. -like LH, hCG stimulates secretory activity of corpus luteum.
Female reproductive cycle
-each cycle takes about 1 month and involves both oogenesis and preparation of the uterus to receive a fertilized ovum. -hormones from hypothalamus, anterior pituitary and ovaries control main events. -encompasses the Ovarian and Uterine Cycles, the hormonal changes that regulate them, and the related cyclical changes in the breast and cervix.
What is the effect of rising but still moderate levels of estrogens on the secretion of GnRH, LH, and FSH?
-effect is negative feedback inhibition of secretion of GnRH, LH, and FSH.
menstrual flow passes:
-from uterine cavity>cervix>vagina>exterior
Hormonal Regulation: FSH- follicle stimulating hormone
-intiates FOLLICULAR GROWTH. -both FSH and LH stimulate the ovarian follicles to secrete estrogens. -androgens are taken up by the granulosa cells of the follicles and then converted into estrogens.
Menstrual phase (menstruation or menses)
-lasts for first 5 days of cycle -first day of menstruation is day 1 of new cyle
Event in one ovary
-matture follicle collapses after ovulation: -basement membrane between ranulosa cells and theca interna breaks down -once blood clot forms, -minor bleeding of ruptured follicle, -becomes corpus hemorrhagicum, -theca internacellsmix w/granulosa cells, -all become transformed into corpus luteum cells under influence of LH. -Stimulated by LH- Corpus lutelum secretes: Progesterone, Estrogen, Relaxin, and INhibin -luteal cells absorb blood clot. -with reference to the ovarian cycle, this phase is called the LUTEAL PHASE.
Relaxin
-produced by corpus luteum. -RELAXES UTERUS by inhibiting contractions of myometrium. -Implantation more likely to occur in a "quiet" uterus. -During pregnancy, placenta produces MORE relaxin, -continues to relax uterine smooth muscle, -End of pregnancy- relaxin increases flexibility of pubic symphysis, -may help dilate uterine cervix.
Estrogens
-promotes development and maintenance of female reproductive structures, secondary sex characteristics, and breasts. -increase PROTEIN ANABOLISM (-eg. building of strong bones. Synergistic w/ human growth hormone (hGH)) -LOWER BLOOD CHOLESTEROL LEVEL. -Moderate levels of estrogens in blood INHIBIT BOTH RELEASE OF GnRH by hypothalamus and SECRETION OF LH AND FSH by anterior pituitary.
Ovulation
-rupture of mature (graafian) follicle, -release of secondary oocyte into pelvic cavity, -Day 14, -Secondary oocyte remains surrounded by its zona pellucida and corona radiata during ovulation. -High levels of ESTROGENS during last part of preovulatory phase, -exerts a positive feedback effect on cells that secrete LH and GnRH and cause ovulation as follows: 1. High concentration of estrogens stimulates more frequent release of GnRH and stimulates gonadotrophs to secrete LH ( ^ ESTROGEN= ^ GnRH= ^LH) 2. GnRH promotes release of FSH and LH (^GnRH=^FSH and ^LH) 3. LH- causes rupture of mature (graafian) follicle and expulsion of a secondary oocyte about 9 hrs after peak of LH surge. Ovulated oocyte and its corona radiata cells are usually swept into the uterine tube.
Inhibin
-secreted by granulosa cells of growing follicles and by corpus luteum after ovulation. -inhibits secretion of FSH and LH (to a lesser extent).
Progesterone
-secreted mainly by cells of CORPUS LUTEUM -cooperates with estrogens: -to prepare and maintain endometrium for implantation of fertilized ovum, -and to prepare mammary glands for milk secretion. -high levels inhibit secretion of GnRH and LH (like moderate levels of estrogens do)
Ovarian Cycle
-series of events in the ovaries. -occur DURING and AFTER the maturation of an oocyte.
Events in the ovaries
-some Secondary follicles in ovaries begin to secrete ESTROGENS and INHIBIN. -day 6= single secondary follicle in one of the two ovaries has outgrown all the others, -becomes dominant follicle. -Estrogens and Inhibin- secreted by dominant folicle- decrease secretion of FSH, -causes other, less well- developed follicles to stop growing and undergo atresia. -Fraternal twins or triplets result when 2 or 3 secondary follicles become codominant and are later ovulated and fertilized at the same time. -one dominant secondary follicle becomes mature (graafian) follicle, -continues to enlarge until ready for ovulation, -blisterlike bulge due to swelling antrum, -continues to increase its production of ESTROGENS.
Hormonal Regulation: LH - Lutenizing hormone.
-stimulates further development of the ovarian follicles -both SHE and LH stimulate ovarian follicles to secrete estrogen. -stimulates production of androgens. -triggers OVULATION. -then promotes formation of the CORPUS LUTEUM. -Corpus Luteum- produces and secretes Estrogens, Progesterone, Relaxin, and Inhibin.
Preovulatory Phase
-time between END OF MENSTRUATION- OVULATION. -more variable in length than other phases. -accounts of MOST OF THE DIFFERENCE IN LENGTH OF CYCLE. -Day 6 - Day 13.
Postovulatory Phase
-time between OVULATION-ONSET OF NEXT MENSES. -Day 15-28. -Most CONSTANT part of female reproductive cycle.
Phases of the female reproductive cycle -28 days; four phases
1. Menstrual Phase. 2. Preovulatory phase. 3. Ovulation. 4. Postovulatory phase.
High levels of estrogens exert a positive feedback effect (green arrows) on the hypothalamus and anterior pituitary, thereby increasing secretion of GnRH and LH
1. high levels of estrogens from almost mature follicles stimulate release of more GnRH and LH. 2. GnRH promotes release of FSH and more LH. 3. LH surge brings about ovulation.
Summary of hormonal interactions in the ovarian and uterine cycles
Declining Estrogen and Progesterone= ^^GnRH=^^FSH and ^^LH = ^^Estrogen.
During menstration
Decrease progesterone and estrogen
__________ are the primary ovarian hormones BEFORE ovulation; After ovulation, both __________ and ____________ are secreted by the corpus luteum
Estrogens; Progesterone and Estrogens.
During follicular phase
Increase E, Increase inhibin by granulosa cells
Presence of ________ in maternal blood or urine is an indicator of pregnancy and is the hormone detected by home pregnancy tests
hCG - Human Chorionic Gonadotropin
When preparing endometrium for arival of fertilized ovum
increase progesterone and estrogen
Evens in the ovaries -
under influence of FSH: -primordial follicles, -primary follicles, secondary follicles. (takes several months for this developmental process to occur) -a follicle that begins to develop at beginnig of menstrual cycle may not reach maturity and ovulate until several menstrual cycles later.
