Menstrual cycle

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Menstrual cycle

  1. 1. The Menstrual Cycle www.freelivedoctor.com
  2. 2. www.freelivedoctor.com
  3. 3. The Menstrual Cycle: Two Phases <ul><li>Ideally 14 days each </li></ul><ul><li>Follicular and Luteal </li></ul><ul><ul><li>Describe changes in the ovary </li></ul></ul><ul><li>Proliferative and Secretory </li></ul><ul><ul><li>Describe changes in the endometrium </li></ul></ul>www.freelivedoctor.com
  4. 4. Hormones in the Menstrual Cycle www.freelivedoctor.com
  5. 5. Follicular phase <ul><li>Begins with the onset of menses and ends on the day of the luteinizing hormone (LH) surge </li></ul><ul><li>During late luteal phase/ early follicular phase: </li></ul><ul><ul><li>withdrawal of estrogen and progesterone in late luteal phase </li></ul></ul><ul><ul><li>In early follicular phase, ovary is least hormonally active  low serum estradiol and progesterone </li></ul></ul><ul><ul><li>release from negative feedback effects of estrogen + progesterone  increase in GnRH pulse frequency in early follicular phase </li></ul></ul><ul><ul><li>Increased GnRH pulse  30% increase in serum FSH concentrations </li></ul></ul><ul><li>FSH release from the pituitary stimulates growth of 5-15 primordial follicles </li></ul><ul><ul><li>By late follicular phase, a single dominant follicle has been selected. </li></ul></ul>www.freelivedoctor.com
  6. 6. Follicular Phase <ul><li>The developing dominant follicle produces estrogen in a 2-cell process </li></ul><ul><ul><li>Theca interna cells produce androstenedione in response to LH stimulation </li></ul></ul><ul><ul><li>Granulosa cells convert androstenedione  estradiol when stimulated by FSH </li></ul></ul><ul><li>Estrogen causes the uterine lining to thicken / proliferate </li></ul><ul><li>GnRH pulse frequency increase  rise in LH </li></ul><ul><li>Rise in LH also stimulates androgen synthesis  androgens are converted to estrogens </li></ul>www.freelivedoctor.com
  7. 7. Follicular Phase <ul><li>Serum estradiol concentrations peak approximately 1 day before ovulation </li></ul><ul><li>Midcycle (~day 14) there is an LH spike in response to this estrogen surge </li></ul><ul><li>Ovulation occurs as increase in LH level causes the follicle to rupture and release mature ovum </li></ul>www.freelivedoctor.com
  8. 8. LH Surge <ul><li>Involves a poorly-understood neuroendocrine phenomenon in which there is a switch from negative feedback control of LH secretion by estradiol and progesterone to positive feedback </li></ul><ul><li>Rising estradiol levels at the end of the follicular phase result in a 10-fold increase in serum LH concentration </li></ul>www.freelivedoctor.com
  9. 9. LH Surge: Effect on the Ovary <ul><li>In response to LH: </li></ul><ul><ul><li>Oocyte in the dominant follicle completes 1 st meiotic division </li></ul></ul><ul><ul><li>Increase in local secretion of plasminogen activator and cytokines required for ovulation </li></ul></ul><ul><ul><li>Oocyte released from follicle at ovarian surface ~ 36 hrs after LH surge. </li></ul></ul><ul><ul><li>Even before oocyte is released, granulosa cells around it begin to “luteinize” and produce progesterone. Progesterone slows LH pulses/ decreases LH pulse frequency </li></ul></ul>www.freelivedoctor.com
  10. 10. Ovulation <ul><li>LH spike stimulates ovulation, the release of the ovum from the follicle </li></ul><ul><li>After ovulation, the luteal phase begins, and remnants of the follicle left behind in the ovary develop into the corpus luteum </li></ul>www.freelivedoctor.com
  11. 11. Ovulation <ul><li>Ovum usually passes into adjoining fallopian tube and is swept down to the uterus by the cilia lining the tube </li></ul><ul><li>Takes 3-4 days for ovum to travel down tube to the uterus </li></ul><ul><li>Fertilization must occur within 24 hrs of ovulation or ovum degenerates </li></ul>www.freelivedoctor.com
  12. 12. Luteal Phase <ul><li>After ovulation, granulosa and theca interna cells lining the wall of the follicle form the corpus luteum cyst (stimulated by LH) </li></ul><ul><li>The corpus luteum synthesizes estrogen and large amounts of progesterone </li></ul><ul><ul><li> Progesterone stimulates the endometrium to become more glandular/secretory in preparation for implantation of fertilized ovum </li></ul></ul>www.freelivedoctor.com
  13. 13. Luteal Phase <ul><li>If fertilization occurs: </li></ul><ul><ul><li>developing trophoblast synthesizes human chorionic gonadotropin (hcg) </li></ul></ul><ul><ul><li>hcg maintains the corpus luteum so it may continue producing estrogen and progesterone to support the endometrium </li></ul></ul><ul><li>By ~ 8-10 weeks gestation, the placenta is developed, and takes over production of estrogen and progesterone </li></ul>www.freelivedoctor.com
  14. 14. Luteal Phase <ul><li>If fertilization does not occur: </li></ul><ul><ul><li>corpus luteum is not maintained by hcg </li></ul></ul><ul><ul><li>Corpus luteum degenerates after ~ 14 days </li></ul></ul><ul><ul><li>Estrogen and progesterone levels fall </li></ul></ul><ul><ul><li>Withdrawal of progesterone causes secretory endometrium to slough </li></ul></ul><ul><ul><li>FSH levels slowly rise again in absence of negative feedback </li></ul></ul><ul><ul><li>↓ </li></ul></ul><ul><ul><li> </li></ul></ul><ul><ul><li> MENSTRUATION </li></ul></ul>www.freelivedoctor.com

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