Menopause Physiology
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Direct answer
Menopause is the permanent cessation of menstruation resulting from exhaustion of the ovarian follicular store, defined clinically after twelve months of amenorrhoea, occurring at a mean age near 51 years (Indian studies place the mean in the mid-to-late forties). With fewer than about a thousand follicles left, granulosa cell inhibin B and anti-mullerian hormone fall, FSH rises first (inhibin's preferred target), and later both FSH and LH climb to high levels while oestradiol drops to postmenopausal concentrations. The consequences — vasomotor hot flushes, urogenital atrophy, and accelerated bone and lipid deterioration — all follow oestrogen withdrawal, and menopausal hormone therapy is decided individually at the lowest effective dose.
What you must remember
- Endocrine sequence of the transition: inhibin B falls first and AMH declines steadily through the reproductive years, so FSH rises before LH; a repeat FSH above about 25-40 IU/L with amenorrhoea supports the diagnosis, taken with low oestradiol.
- Perimenopause is hypergonadotropic but erratic: residual follicles produce fluctuating oestradiol, causing irregular cycles, heavy anovulatory bleeding and surprisingly high oestradiol episodes — hormone levels in one blood sample are unreliable in the transition.
- Hot flushes: sudden warmth over chest and face lasting 1-5 minutes with sweating and tachycardia; a narrowed hypothalamic thermoneutral zone, linked to oestrogen withdrawal and kisspeptin-neurokinin signalling; the cardinal vasomotor symptom, worse at night.
- Bone: accelerated trabecular resorption in the first 5-10 years after menopause — the postmenopausal osteoporosis window, assessed by DEXA, managed with calcium, vitamin D, exercise and antiresorptives when indicated.
- Metabolic changes: LDL cholesterol rises and HDL falls slightly, body fat redistributes centrally, and insulin sensitivity worsens — cardiovascular risk accelerates after menopause.
- Urogenital atrophy: oestrogen-dependent epithelium of vagina, urethra and pelvic floor thins, causing dyspareunia, dryness and recurrent urinary symptoms; topical oestrogen helps systemically poor candidates.
- HRT principles: combined oestrogen-progestogen for a woman with a uterus, oestrogen alone after hysterectomy; prescribed ideally within ten years of menopause and below 60 years, at the lowest effective dose, per current guidance.
How to work through a perimenopausal clinic visit
A 48-year-old with cycles shortened to 21 days alternating with three-month gaps, night sweats and heavy menses. First exclude pathology: a pregnancy test, thyroid profile (thyroid dysfunction mimics vasomotor symptoms), endometrial assessment for the heavy bleeding — anovulatory cycles in the transition are the usual cause, but endometrial sampling is done when bleeding is heavy or prolonged in this age group (Indian teaching favours sampling after 40 years with abnormal bleeding).
Then explain the physiology to frame treatment. The night sweats and flushes usually ease over two to five years as the thermoneutral zone readjusts, so the decision to treat is about severity: menopausal hormone therapy is the most effective agent for vasomotor symptoms, adding a progestogen to protect the endometrium because unopposed oestrogen drives hyperplasia. For a woman with only genitourinary symptoms, topical vaginal oestrogen avoids systemic exposure. Bone health needs calcium about 1000-1200 mg daily with vitamin D, weight-bearing exercise, and DEXA when risk factors exist, since the fastest bone loss occurs in the first postmenopausal decade. Contraception continues for twelve months after the last period, because residual follicles can still ovulate erratically — a frequently missed practical point.
Where students slip
Two slips recur. First, students call menopause a state of "high oestrogen" because cycles become erratic; late perimenopause has fluctuating, sometimes high oestradiol from residual follicles against a background of failing follicle reserve — the FSH rise is the truthful axis signal. Second, the claim that FSH rises because the pituitary is hyperactive; the pituitary responds appropriately to lost inhibin and oestradiol feedback — remove the ovary and FSH climbs within days. Viva examiners also probe why menopause does not occur in males: spermatogenesis and Leydig function decline gradually (andropause is not a sudden follicle-depletion event) because the testis renews its cellular workforce, unlike the finite ovarian follicle pool fixed before birth.
Frequently asked questions
Why does FSH rise earlier and higher than LH at menopause?
Inhibin B from granulosa cells selectively suppresses FSH; as follicles vanish, inhibin B falls first, releasing FSH before the oestradiol fall fully removes feedback on both gonadotrophins.
What causes the hot flush of menopause?
Oestrogen withdrawal narrows the hypothalamic thermoneutral zone so small core-temperature rises trigger heat-dissipating responses — flushing and sweating — mediated in part by neurokinin B and kisspeptin neurons in the hypothalamic tuberomammillary region.
What is the average age and definition of menopause?
Mean age about 51 years globally, with Indian means typically in the mid-to-late forties; clinically defined retrospectively after twelve consecutive months of amenorrhoea.
Why is bone loss accelerated after menopause?
Oestradiol normally restrains osteoclast activity; its withdrawal removes the brake, and RANKL-driven resorption outstrips formation, fastest in trabecular bone — vertebrae and distal forearm fracture first.
Which women can receive oestrogen-only hormone therapy?
Women who have had a hysterectomy; those with an intact uterus need added progestogen to prevent endometrial hyperplasia from unopposed oestrogen, per current prescribing guidance.