LEC 34: OVARIAN AND UTERINE CYCLES

• Phases of Ovarian Cycle

  1. Follicular Phase

  2. Ovulation

  3. Luteal Phase
• Follicular Phase


  • Development of ovarian follicle
  • Maturation of oocyte within the follicle
• Ovulation


  • Rupture of mature follicle
  • Releases secondary oocyte
  • Peak in LH secretion
• Luteal Phase


  • Transformation of ruptured follicle into corpus luteum
  • Secretion of progesterone and some estrogen by corpus luteum
• Hormonal Regulation


  1. GnRH from hypothalamus stimulates release of FSH and LH

  2. FSH promotes growth and development of ovarian follicles

  3. Rising estrogen levels = negative feedback = inhibits release of GnRH, FSH, LH

  4. Peak estrogen levels = positive feedback = surge in LH secretion = triggers ovulation

  5. After ovulation: Corpus luteum secretes progesterone, inhibits release of GnRH, FSH, LH

  6. If fertilization occurs: Corpus luteum persists, maintains hormone secretion until placenta takes over

  7. If fertilization doesn't occur: Corpus luteum degenerates, decline in hormone levels and start of new ovarian cycle
• Estrogen


  • Growth and development of female reproduction structures
  • Supports oogenesis and follicle growth in ovaries
  • Induce secondary sex characteristics during puberty
  • Widening and lightening of pelvis
  • Stimulates metabolic changes
• Progesterone


  • Prepares endometrium for implantation of embryo
  • Inhibit further release of GnRH, FSH, & LH after ovulation
  • Maintains secretory mucosa in endometrium
  • Forms a cervical plug to block entry of sperm or pathogens
  • Sustain development of embryo until placenta is mature
• Functions of Uterine Cycle

  1. Prepare endometrium for implantation of a fertilized ovum

  2. Provide suitable environment for embryonic development

  3. Facilitate the shedding of the endometrial lining if fertilization does not occur
• Regulation of Uterine Cycle

  1. Menstrual Phase (Days 1-5): Lowest ovarian hormone levels, shedding of endometrial lining

  2. Proliferative Phase (Days 6-14): Rising estrogen levels, rebuilds endometrial layer

  3. Secretory Phase (Days 15-28): High levels of estrogen & progesterone, prepares endometrium for embryo implantation, cervical mucous thickens, spiral arteries convert endometrial layer into a secretory mucosa, corpus luteum degenerates if fertilization doesn't occur, leads to decline in progesterone and estrogen levels, shedding off the endometrial layer
• Anovulation: ovulation does not occur, luteal phase is short, not enough progesterone for fertility
• Polycystic ovary syndrome: anovulation, increased testosterone production by ovaries
• rising estrogen levels in blood plasma triggers what?

  inhibits the release of GnRH, FSH, LH
• peak estrogen levels in follicle causes what?

  causes a surge in LH secretion which triggers ovulation
• what happens when fertilization occurs?


  corpus luteum persists and maintains hormone secretion until placenta takes over
• what happens when fertilization doesn't occur?

  corpus luteum degenerates, decline in hormone levels, and start of new ovarian cycle
• what happens when fertilization does not occur?

  shedding of endometrial layer
• what are the phases of the ovarian cycle?

  follicular, ovulation, luteal phase
• development of ovarian follicle, maturation of oocyte within the follicle occurs in what phase of the ovarian cycle?

  follicular phase
• rupturing of mature follicle and the release of secondary oocyte happens in what phase of the ovarian cycle?

  ovulation
• transformation of ruptured follicle into corpus luteum and secretion of progesterone and some estrogen occurs in what phase of the ovarian cycle?

  luteal phase