Menopause & Andropause

BCH 130 — Advanced Human Biochemistry · Dr. Radi

build Jul 18 · 08:24 · CC BY-NC-SA 4.0 · owned figures (RDKit / matplotlib)
Dr. Radi

By the end of this unit, you can…

  • Explain the endocrinology of the menopausal transition
  • Connect estrogen withdrawal to vasomotor symptoms and the biochemistry of hot flashes (KNDy neurons / thermoregulatory setpoint).
  • Trace the systemic consequences of chronic estrogen loss
  • Explain hormone-replacement therapy — estrogen +/- progestin, routes, benefits/risks — as targeted replacement of the deficient hormone.
Dr. Radi

Today's route 🗺️

  1. The Menopausal Transition
  2. Menopause — Systemic Effects & HRT
  3. Andropause & Male Reproductive Aging
Dr. Radi

1 · The Menopausal Transition

"Menopause isn't a hormone running low — it's a gland running OUT. Watch the HPG axis lose its ovarian brakes: follicles deplete, inhibin and estradiol fall, and FSH and LH climb. Then we'll trace that estrogen withdrawal all the way up to the hot flash."

Dr. Radi

The ovarian brakes come off

You've met the HPG axis — now watch it lose its off switch. A woman is born with every follicle she'll ever have, and the pool runs down. As it empties, granulosa cells make less inhibin B and estradiol — the very hormones that restrained the pituitary. Brakes gone, FSH and LH climb.

Dr. Radi

FSH rises first

Here's the tell: the hormones don't all move together. Inhibin B falls first, so its brake on the pituitary lifts early and FSH creeps up years before periods stop. Estradiol lurches through the erratic perimenopause, then crashes at the final period — high FSH, low estradiol is the fingerprint.

Dr. Radi

Where hot flashes come from

So why the hot flashes? In the hypothalamus sit KNDy neurons, normally kept quiet by estradiol. Withdraw the estrogen and they hypertrophy and fire, flooding the preoptic thermostat with neurokinin B. The thermoneutral zone narrows to a sliver — a trivial warmth triggers a full flush. Blocking NK3R (fezolinetant) calms it.

Dr. Radi

2 · Menopause — Systemic Effects & HRT

"Estrogen was quietly protecting four systems at once — bone, heart, urogenital tract, and metabolism. Take it away for good and each one drifts. Then the fix that follows straight from the mechanism: replace the deficient hormone, and know exactly when to add a progestin."

Dr. Radi

One deficiency, four systems

Menopause isn't just symptoms — it's decades of estrogen withdrawal, and estrogen was quietly protecting four systems at once. Bone loses its brake on resorption. The cardiovascular profile turns (LDL up, HDL down). Urogenital tissues thin and atrophy. And metabolism shifts toward belly fat and insulin resistance. One deficiency, four fronts.

Dr. Radi

Estrogen was the brake on bone

Zoom in on bone, where the loss runs fastest — up to 20% in the first years. Estradiol is the brake on the osteoclast: it lowers RANKL, raises the decoy OPG, and shortens the osteoclast's life. Pull estrogen out and the osteoclast is unleashed — resorption outruns formation, and bone thins toward osteoporosis.

Dr. Radi

Replace the missing hormone

The fix is logical: replace the missing hormone. Estrogen melts hot flashes, protects bone, and restores urogenital tissue. But unopposed estrogen overgrows the endometrium — so with a uterus, add a progestin to guard it. Route matters: oral raises clot risk (first-pass liver); the patch avoids it. Best started near menopause.

Dr. Radi

3 · Andropause & Male Reproductive Aging

"Do men have a menopause? Not really — and the difference is the whole point. Where the ovary fails like a cliff, the testis drifts down a gentle slope. We'll watch total testosterone, free testosterone, and SHBG pull apart with age, then weigh testosterone-replacement therapy honestly."

Dr. Radi

A cliff versus a slope

Do men have a "menopause"? Not really — and this graph is why. The ovary fails like a cliff: estradiol plummets over a couple of years around 51. Testosterone instead drifts down a gentle slope, roughly 1% per year from your thirties. Gradual, partial, and never complete — men stay fertile for decades.

Dr. Radi

The free-testosterone squeeze

Here's the subtlety. As men age, total testosterone only dips a little — but SHBG rises, gripping more of it tightly. Since only free and albumin-bound T is usable, the bioactive fraction shrinks far more than the total does. So read free testosterone, not just total, or you'll miss it.

Dr. Radi

Testosterone therapy, honestly

If a man has real symptoms plus low morning testosterone, replacement helps — but know the biochemistry. Exogenous T feeds back and shuts down the HPG axis, so LH and FSH fall and the testes shrink and sperm dries up. Some aromatizes to estradiol (gynecomastia), and it revs erythropoiesis — watch the hematocrit for clot risk.

Dr. Radi

Can you…?

  • ☐ explain the endocrinology of the menopausal transition?
  • ☐ connect estrogen withdrawal to vasomotor symptoms and the biochemistry of hot flashes (KNDy neurons / thermoregulatory setpoint).?
  • ☐ trace the systemic consequences of chronic estrogen loss?
  • ☐ explain hormone-replacement therapy — estrogen +/- progestin, routes, benefits/risks — as targeted replacement of the deficient hormone.?

If any box stays empty, the practice site has a drill for it. 🧪

Dr. Radi