Reproductive System-L3 Faisal I. Mohammed, MD, PhD University of Jordan

The Female Reproductive Cycle Encompasses ovarian and uterine cycle, hormonal changes that regulate them, and related changes in breast and cervix Ovarian cycle – series of events in ovaries that occur during and after maturation of oocyte Uterine (menstrual) cycle – concurrent series of changes in uterine endometrium preparing it for arrival of fertilized ovum University of Jordan

Hormonal regulation Gonadotropin-releasing hormone (GnRH) Secreted by hypothalamus controls ovarian and uterine cycle Stimulates release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from anterior pituitary FSH Initiate follicular growth Stimulate ovarian follicles to secrete estrogens University of Jordan

Hormonal regulation…cont LH Stimulates further development of ovarian follicles Stimulate ovarian follicles to secrete estrogens Stimulates thecal cells of developing follicle to produce androgens to be converted into estrogens Triggers ovulation Promotes formation of corpus luteum – produces estrogens, progesterone, relaxin and inhibin University of Jordan

Hormonal regulation Estrogens secreted by ovarian follicles Promote development and maintenance of female reproductive structures and secondary sex characteristics Increases protein anabolism including building strong bones Lowers blood cholesterol Inhibit release of GnRH, LH and FSH Progesterone Secreted mainly by corpus luteum Works with estrogens to prepare and maintin endometrium for implantation and mammary glands for milk production Inhibits secretion of GnRH and LH University of Jordan

Hormonal regulation Relaxin Produced by corpus luteum Relaxes uterus by inhibiting contraction of myometrium At end of pregnancy, increases flexibility of pubic symphysis and dilates uterine cervix Inhibin Secreted by granulosa cells of growing follicles and by corpus luteum Inhibits secretion of FSH and LH University of Jordan

Secretion and physiological effects of hormones in the female reproductive cycle University of Jordan

4 Phases Typical duration 21-35 days Assume a duration of 28 days Menstrual phase Preovulatory phase Ovulation Postovulatory phase University of Jordan

The female reproductive cycle University of Jordan

Menstrual phase or menstruation Roughly first 5 days of cycle First day of menstruation is day 1 of new cycle Events in ovaries Under FSH influence, several primordial follicles develop into primary follicles ad then into secondary follicles Takes several months Follicle that begins to develop in one cycle may not mature for several cycles later University of Jordan

Menstrual phase or menstruation…cont Events in uterus Menstrual discharge occurs because declining levels of estrogens and progesterone stimulate release of prostaglandins causing uterine spiral arterioles to constrict Cells deprived of oxygen begin to die Only stratum basilis remains University of Jordan

Preovulatory phase More variable in length Lasts from days 6-13 in a 28 day cycle Events in ovaries Some of secondary follicles begin to secrete estrogens and inhibin Dominant follicle – one follicle outgrown all others Estrogens and inhibin of dominant follicle decrease FSH causing other follicles to stop growing Fraternal (nonidentical) twins result when 2 or 3 secondary follicles become codominant and are ovulated and fertilized at the same time University of Jordan

Preovulatory phase Normally, one dominant follicle becomes the mature (graffian) follicle In ovarian cycle, menstrual and preovulatory phases are termed follicular phase because follicles are growing Events in uterus Estrogens stimulate repair of endometrium Cells of stratum basalis undergo mitosis to form new stratum functionalis Thickness of endometrium doubles In uterine cycle, preovulatory phase is the proliferative phase because endometrium is proliferating University of Jordan

Ovulation Rupture of mature (graffian) follicle and release of secondary oocyte Day 14 of 28 day cycle High levels of estrogens exert a positive feedback effect on cells secreting LH and GnRH Fertilization can occur after ovulation Sperms can live 48-72 hours inside the femal reproductive tract Ovum can be fertilized within 48 hours after ovulation The best time for fertilization and conception (pregnancy) is to have sexual intercourse 48-72 hours before ovulation to 48 hours after ovulation Period before that time and after that time is called the safe period and it is the principle for physiological contraception method University of Jordan

Ovulation High levels of estrogens from almost mature follicle stimulate release of more GnRH and LH LH surge brings about ovulation Ovulated secondary oocyte Hypothalamus Anterior pituitary GnRH promotes release of FSH and more LH Ovary Corpus hemorrhagicum (ruptured follicle) Almost mature (graafian) follicle LH GnRH 1 2 3 High levels of estrogens from almost mature follicle stimulate release of more GnRH and LH Hypothalamus Anterior pituitary GnRH promotes release of FSH and more LH Ovary Corpus hemorrhagicum (ruptured follicle) Almost mature (graafian) follicle LH GnRH 1 2 High levels of estrogens from almost mature follicle stimulate release of more GnRH and LH Hypothalamus Anterior pituitary Ovary Corpus hemorrhagicum (ruptured follicle) Almost mature (graafian) follicle LH GnRH 1 Ovulation University of Jordan

Postovulatory phase Duration most constant of phases Lasts for 14 days in 28 day cycle (day 15-28) Events in one ovary After ovulation, mature follicle collapses to form corpus luteum under the influence of LH Secretes progesterone, estrogen, relaxin and inhibin In the ovarian cycle, this is the luteal phase University of Jordan

Corpus luteum If oocyte not fertilized, corpus luteum lasts 2 weeks Degenerates in corpus albicans As levels of progesterone, estrogens and inhibin decrease, release of GnRH, FSH, and LH rise sue to loss of negative feedback Follicular growth resume as new ovarian cycle begins If oocyte is fertilized, corpus luteum lasts more than 2 weeks Human chorionic gonadotropin (hCG) produced by chorion of embryo about 8 days after fertilization stimulates corpus luteum University of Jordan

Events in uterus Progesterone and estrogens produced by corpus luteum promote growth of endometrium Because of secretory activity of endometrial glands, this is the secretory phase of uterine cycle Changes peak about 1 week after ovulation when a fertilized ovum might arrive in uterus If fertilization does not occur, levels of progesterone and estrogens decline due to degeneration of corpus luteum Withdrawal of estrogens and progesterone causes menstruation University of Jordan

Hormonal interactions in the ovarian and uterine cycles University of Jordan

Breast / Mammary glands University of Jordan

Breast / Mammary glands Nipple has openings of lactiferous ducts Areola – pigmented area Mammary gland – modified sudoriferous gland that produces milk 15-20 lobes divided into lobules composed of alveoli (milk-secreting glands) Estrogen promotes the development of the ductal system of the breast Progesterone promotes the development of the alveolar system –milk secretory system- University of Jordan

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