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Human Physiology II · Systems Physiology

Female Reproductive Physiology

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On this page 7 sections
  1. In 30 seconds
  2. Why this matters
  3. The college version
  4. Eli explains
  5. Worked example
  6. Key takeaway
  7. Study tools

In 30 seconds

The female reproductive system produces one mature egg per cycle and prepares the uterus to receive it. produces the oocyte while matures its surrounding follicle. The ovarian cycle (, , ) is driven by FSH and LH; rising estrogen triggers a mid-cycle that causes ovulation, and the luteal phase produces progesterone. These ovarian hormones drive the uterine cycle (, proliferative, secretory), and the depletion of follicles at ends the cycles.

Why this matters

The ovarian and uterine cycles are assessed through hormone levels (FSH, LH, estradiol, progesterone) and clinical timing of ovulation (e.g., the LH surge). Menopause is confirmed by persistently elevated FSH with low estrogen, a direct consequence of lost negative feedback. Reference ranges and diagnostic criteria vary by institution and jurisdiction, and these notes support education and do not replace clinical instruction; any concerning symptoms require evaluation by qualified clinicians.

The college version

1. Oogenesis and folliculogenesis prepare a single egg

Oogenesis is the formation of the haploid egg, beginning before birth and pausing in meiosis until ovulation. Folliculogenesis is the maturation of the follicle — the oocyte plus its surrounding granulosa and theca cells — from a primordial follicle through primary and secondary (antral) stages to a mature Graafian (preovulatory) follicle.

2. The ovarian cycle has three phases

The follicular phase is dominated by FSH-driven follicle growth and rising estrogen. Ovulation, triggered by the LH surge, releases the oocyte. The luteal phase is dominated by the corpus luteum, which secretes progesterone (and some estrogen) to support a potential pregnancy.

3. The uterine cycle mirrors the ovarian cycle

The menstrual (uterine) cycle responds to ovarian hormones: menses (shedding of the functional layer when hormones fall), the (endometrial regrowth under estrogen), and the (glandular secretion and readiness for implantation under progesterone).

How it works

  1. FSH matures a follicle; its granulosa cells produce estrogen.
  2. Rising estrogen builds the uterine lining (proliferative phase) and then triggers the LH surge.
  3. The LH surge causes ovulation and forms the corpus luteum.
  4. Progesterone drives the secretory phase and suppresses the axis.
  5. If no pregnancy occurs, the corpus luteum regresses, hormones fall, and menses follows.
  6. Follicle depletion at menopause lowers estrogen and raises FSH/LH.

Common confusions

Do not confuseWithDifference
OogenesisFolliculogenesisOogenesis makes the egg; folliculogenesis matures the surrounding follicle
Follicular phaseLuteal phaseFollicular = FSH/estrogen growth; luteal = corpus luteum/progesterone
Proliferative phaseSecretory phaseProliferative is estrogen-driven regrowth; secretory is progesterone-driven secretion
Negative feedbackPositive feedback (LH surge)Estrogen normally inhibits the axis but, sustained at high levels, briefly stimulates the LH surge

Memory aids

"F-O-L-P" for the cycle — Follicular (estrogen), Ovulation (LH surge), Luteal (progesterone) — and for the uterus, "M-P-S" (Menses, Proliferative, Secretory). Remember "E before P": Estrogen rises first, then Progesterone.

Quick review

Topic Recap

Each cycle, FSH matures a follicle whose granulosa cells produce estrogen. Rising estrogen rebuilds the endometrium and, through positive feedback, triggers the LH surge that causes ovulation. The corpus luteum then secretes progesterone, driving the secretory phase and suppressing the axis. Without pregnancy, the luteal hormones fall and menses occurs; at menopause, follicle depletion removes negative feedback and FSH/LH rise.

Knowledge Check

  1. What event is triggered by the mid-cycle LH surge?
  2. Which hormone dominates the luteal phase, and what does it do to the endometrium?
  3. How does estrogen's feedback action change between early and late follicular phase?
  4. Which uterine phase corresponds to falling progesterone and estrogen at the end of a non-pregnant cycle?
  5. Why do FSH and LH rise at menopause?

Answers and Rationales

  1. Ovulation — the LH surge resumes meiosis and causes the mature follicle to rupture and release the secondary oocyte.
  2. Progesterone, which drives the secretory phase by thickening and stabilizing the endometrium and stimulating glandular secretion.
  3. Early on, estrogen exerts negative feedback (suppressing FSH/LH), but late in the follicular phase, sustained high estrogen switches to positive feedback, triggering the LH surge.
  4. Menses — the fall in progesterone and estrogen after corpus-luteum regression causes the functional layer of the endometrium to shed.
  5. Because the follicle pool is depleted, so estrogen and progesterone fall and their negative feedback on the pituitary is lost, allowing FSH and LH to rise.
Eli, the EliExplains learning guide

Eli explains

The same idea, in plain words

Explain it like I’m 10

Think of the ovary as a garden that matures one flower (follicle) each month. Early in the month, a hormone "fertilizer" (FSH) helps several buds grow; one becomes dominant. Mid-month, a sudden spike of another signal (the LH surge) makes that flower open and release its seed (the egg = ovulation). The spent flower then turns into a temporary gland (corpus luteum) that makes progesterone to keep the soil (the uterine lining) ready for a seed. If no seed implants, the lining sheds and the cycle starts over. The comparison stops being exact because the system uses both negative and positive feedback — unusually, a rising hormone (estrogen) switches from suppressing the brain to stimulating a surge, a reversal that has no simple garden analogy.

Simple Example

Rising estrogen late in the follicular phase is like a thermostat that, instead of turning off the furnace when the room heats up, briefly cranks it higher — producing the LH surge that pops the egg.

Worked example

  1. Follicular phase: Hypothalamic GnRH drives pituitary FSH and LH. FSH stimulates a cohort of follicles; granulosa cells convert androgens (from theca cells) into estrogen via aromatase. One follicle becomes dominant and estrogen rises.
  2. Positive feedback and the LH surge: Late in the follicular phase, high, sustained estrogen switches to positive feedback on the pituitary and hypothalamus, triggering a massive LH (and smaller FSH) surge.
  3. Ovulation: The LH surge resumes meiosis in the oocyte and, about 24–36 hours later, causes follicle rupture and release of the secondary oocyte.
  4. Luteal phase: The ruptured follicle becomes the corpus luteum, secreting progesterone and estrogen. Progesterone thickens and stabilizes the endometrium (secretory phase) and suppresses GnRH/LH via negative feedback.
  5. Without pregnancy: The corpus luteum regresses (~14 days), progesterone and estrogen fall, and the endometrium sheds (menses). Falling steroid levels release the axis from inhibition, and a new cycle begins.
  6. With pregnancy: hCG from the implanting embryo rescues the corpus luteum, maintaining progesterone (see Topic 31).
  7. Menopause: As the finite ovarian follicle pool is depleted, estrogen and progesterone fall, removing negative feedback, so FSH and LH rise. Cycles cease, marking menopause.

Key takeaways

  • High yield: Estrogen late in the follicular phase exerts positive feedback, producing the LH surge that triggers ovulation — a rare positive-feedback loop in endocrinology.
  • High yield: The corpus luteum secretes progesterone (and estrogen) during the luteal phase.
  • High yield: The uterine cycle is driven by the ovarian cycle: estrogen → proliferative phase; progesterone → secretory phase.
  • High yield: Progesterone exerts negative feedback, suppressing GnRH/LH during the luteal phase.
  • Oogenesis pauses in meiosis and only completes maturation at fertilization; ovulation releases a secondary oocyte.
  • The follicular phase is variable in length; the luteal phase is a fairly constant ~14 days.
  • High yield: At menopause, depleted follicles lower estrogen/progesterone, so FSH and LH rise because negative feedback is lost.
  • Theca cells produce androgens that granulosa cells aromatize to estrogen — the "two-cell" model of estrogen synthesis.

Keep learning

Ready to build on this? Continue to the next lesson.

Study tools & related lessonsYou’ll learn to · Key vocabulary · Related

You’ll learn to

  • Describe oogenesis and folliculogenesis, from primordial follicles to ovulation.
  • Outline the ovarian cycle (follicular phase, ovulation, luteal phase) and the hormones driving each stage.
  • Relate the uterine (menstrual) cycle — menses, proliferative, and secretory phases — to ovarian hormones.
  • Explain the HPG axis in females, including the estrogen/LH-surge positive feedback and negative feedback, and the hormonal changes of menopause.

Key vocabulary

Oogenesis
Formation of the haploid egg
Folliculogenesis
Maturation of the follicle around the oocyte
Follicular phase
FSH-driven follicle growth and rising estrogen
Ovulation
Release of the oocyte at the LH surge
Luteal phase
Corpus-luteum phase dominated by progesterone
Menses
Shedding of the endometrial lining
Proliferative phase
Estrogen-driven endometrial regrowth
Secretory phase
Progesterone-driven glandular secretion
LH surge
Mid-cycle spike of LH from estrogen positive feedback
Menopause
Cessation of cycles from follicle depletion

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