Menstrual Cycle

🔑 Puberty & Reproductive Hormones

  • Endocrine system: glands release hormones into blood → target organs.

  • Male (testes): produce testosterone → stimulates sperm production, causes secondary sexual characteristics.

  • Female (ovaries): produce estrogen → stimulates development of secondary sexual characteristics & menstrual cycle.

  • Puberty: reproductive hormones cause changes (e.g. pubic hair, sperm production, egg maturation).

📅 Menstrual Cycle Overview (28 days)

  • Day 1–14: Egg matures in ovary.

  • Day ~14: Ovulation → ovary releases egg.

  • Uterus lining: becomes thick & spongy to prepare for possible fertilized egg.

  • If fertilization happens → egg implants in uterus wall → pregnancy.

  • If not fertilized → egg + uterus lining shed → period.

🧪 Key Hormones & Their Roles

  • FSH (Follicle-Stimulating Hormone) – from pituitary.

    • Causes egg to mature in ovary.

    • Stimulates ovary to release estrogen.

  • LH (Luteinizing Hormone) – from pituitary.

    • Triggers ovulation (release of egg).

  • Estrogen – from ovary.

    • Thickens uterus lining.

    • Inhibits FSH (to stop more eggs maturing).

    • Stimulates LH release.

  • Progesterone – from ovary (after ovulation).

    • Maintains thick uterus lining.

    • Inhibits FSH and LH (prevents further eggs from maturing).

    • If no fertilization → progesterone levels fall → lining breaks down (period).

🔄 Hormone Interactions (Higher Tier)

  1. FSH rises → egg matures + ovary makes estrogen.

  2. Estrogen rises → builds uterus lining + stops FSH + triggers LH.

  3. LH peak (day ~14) → ovulation.

  4. Progesterone rises (after ovulation) → maintains uterus lining + stops FSH & LH.

  5. If no fertilization → progesterone falls → period.

📊 Hormone Graph (exam tip)

  • FSH high at start → falls as estrogen rises.

  • Estrogen peaks → triggers LH surge.

  • LH peaks → ovulation.

  • Progesterone peaks after ovulation → falls if no pregnancy → menstruation.

  • Acronnym:

    • F → FSH

    • O → Oestrogen

    • L → LH

    • P → Progestrone

✅ Exam tips:

  • Foundation: just learn functions of the 4 hormones.

  • Higher: explain interactions (FSH → Estrogen → LH → Progesterone).

  • Be prepared to interpret hormone graphs (know timing/order of peaks).