Female Reproductive Physiology

Female Reproductive Physiology - Eggcellent Adventures

• Folliculogenesis: Maturation journey from primordial follicle → primary → secondary → mature Graafian follicle (~20mm).
• Two-Cell, Two-Gonadotropin Theory:
  • Theca cells (LH stimulation): Synthesize androgens.
  • Granulosa cells (FSH stimulation): Convert androgens to estrogen via aromatase.
• Ovulation: LH surge (peaks 24-36h before) triggers release of oocyte.

  ⭐ The LH surge, triggered by sustained high estrogen levels (positive feedback), is essential for ovulation.

• Luteal Phase:
  • Corpus Luteum: Forms post-ovulation; secretes progesterone (maintains endometrium).
  • Corpus Albicans: Scar tissue if no pregnancy.

Female Reproductive Physiology - Monthly Makeover

Uterine cycle (21-35 days); menses 2-7 days. 📌 M-PES (Menstrual, Proliferative-Estrogen, Secretory-Progesterone).

• Menstrual Phase (Days 1-5):
  • ↓Progesterone → spiral artery spasm, endometrial shedding.
• Proliferative Phase (Days 6-14, variable):
  • Estrogen-driven: endometrial growth, glands & spiral arteries elongate.
• Secretory Phase (Days 15-28, fixed ~14 days):
  • Progesterone-dominant: glandular tortuosity & secretion (glycogen, mucus), spiral arteries coil. Decidualization for implantation.
  • No implantation: ↓progesterone → menstruation.

⭐ The secretory phase endometrium, rich in glycogen and mucus, is prepared by progesterone for potential implantation.

Female Reproductive Physiology - Hormone Harmony

• Hypothalamus: Secretes GnRH (pulsatile) → stimulates Ant. Pituitary.
• Ant. Pituitary: Releases FSH (follicle growth) & LH (ovulation/corpus luteum) → act on Ovary.
• Ovary Hormones & Feedback Loops:
  • Estrogen:
    • Low/Moderate levels: Negative feedback on FSH/LH (↓).
    • Sustained High (pre-ovulatory): Positive feedback → LH surge (↑).
  • Progesterone: Strong negative feedback on GnRH/LH/FSH (↓).
  • Inhibin B (granulosa cells): Negative feedback, selectively ↓FSH.
  • Activin (granulosa cells): Positive feedback, stimulates ↑FSH.

⭐ Inhibin B, produced by granulosa cells under FSH stimulation, selectively inhibits FSH secretion from the anterior pituitary.

Female Reproductive Physiology - Conception & Kick-off

• Gamete Transport & Fertilization:
  • Sperm: Capacitation & acrosome reaction.
  • Ovum: Picked up by fimbriae.
  • Fertilization site: Ampulla of fallopian tube.

    ⭐ Fertilization typically occurs in the ampulla of the fallopian tube, the widest part of the tube.

• Early Development: Zygote → Morula → Blastocyst (Inner cell mass & Trophoblast).
• Implantation (Day 6-10 post-ovulation): Apposition, Adhesion, Invasion.
  • Trophoblast differentiates: Syncytiotrophoblast (produces hCG) & Cytotrophoblast.
• hCG (Human Chorionic Gonadotropin):
  • Rescues corpus luteum; basis of pregnancy tests.
  • Detectable in serum: 8-11 days post-conception.
  • Doubles every 48-72 hours in early viable intrauterine pregnancy.

Female Reproductive Physiology - The Grand Pause

• Menopause: 12 months amenorrhea post-FMP. Avg. age ~51 (45-55 yrs). Perimenopause is transition.
• Cause: Ovarian follicle depletion → ↓Estrogen, ↓Inhibin → ↑FSH (diagnostic, >30-40 mIU/mL), ↑LH.
• Features: Vasomotor (hot flashes), urogenital atrophy, mood/sleep issues, osteoporosis risk.

⭐ Markedly elevated serum FSH levels (e.g., > 30-40 mIU/mL) are a hallmark of menopause due to loss of negative feedback from ovarian estrogen and inhibin.

High‑Yield Points - ⚡ Biggest Takeaways

• Menstrual cycle is orchestrated by GnRH, FSH, LH, estrogen, and progesterone.
• Ovulation is triggered by an LH surge, typically around day 14.
• Corpus luteum produces progesterone to maintain the endometrium.
• Fertilization usually occurs in the ampulla of the fallopian tube.
• hCG (human chorionic gonadotropin) maintains the corpus luteum in early pregnancy.
• Estrogen is responsible for secondary sexual characteristics and endometrial proliferation.
• Progesterone is the "pregnancy hormone," promoting endometrial secretion and uterine quiescence.