Start Here
Figure It Out First
Rule them out one by one. Last one standing wins.
🩺 23-year-old female runner. Lost 18 lbs training for a marathon. No period for 5 months.
Four things could explain this. Each clue eliminates one. Click the one the clue rules out.
Pregnancy
hCG stops FSH/LH → no cycle
PCOS
androgen excess, anovulation
Prolactinoma
↑ prolactin suppresses GnRH
Energy Deficiency
endometrium can't divide
Clue 1 of 3
Urine hCG is negative.
The Mechanism
How ATP Depletion Stops the Cycle
Tap to reveal each step — build the chain yourself.
1
⚡ ATP Depleted
Severe caloric restriction, malnutrition, or extreme exercise. Energy supply can't meet demand. Cellular ATP drops.
2
🔴 Endometrial Cells Can't Divide
The endometriumThe inner lining of the uterus — a rapidly dividing tissue that thickens every cycle, ready to receive a fertilized egg. Requires massive ATP for monthly cell division and vascular proliferation. is a rapidly dividing cell line. Monthly proliferation costs enormous ATP. No ATP → cells stall, lining stays thin.
3
🩸 No Lining → No Shedding
If the endometrium never builds up, there's nothing to shed. Result: menstruation stops →
secondary amenorrhea.
🔑Can't shed what was never built. No ATP = no proliferation = no period. The uterus went on an energy budget.
4
🚫 No Nourishment for Implantation → Sterility
Even if fertilization occurs, a fertilized egg needs a lush, vascular endometrial lining to implant and get nutrients from. A thin, non-functional endometrium can't support it. The egg can't implant → sterility.
Board Trap: Secondary vs. Primary Amenorrhea
Primary amenorrhea = never had a period (structural/genetic cause). Secondary amenorrhea = had periods, then stopped (functional cause — like this). Low energy state → secondary amenorrhea. Don't swap them.
Same Mechanism, Other Organs
Blood Vessels & Bladder
Two more rapidly dividing epithelial linings that fail when ATP drops.
Blood Vessel Endothelium
Rapidly dividing cell: endothelial cellsEndothelial cells line every blood vessel and must constantly divide to repair micro-damage from shear stress, turbulent flow, and oxidative stress. Their turnover rate is high — they're energy-hungry.
No ATP → can't repair vessel lining → endothelium breaks down → increased vascular permeability, impaired vasodilation, failure to prevent clot formation on damaged walls.
Bladder (Urothelium)
Rapidly dividing cell: transitional epitheliumTransitional epithelium (urothelium) lines the bladder and urinary tract. It constantly renews to withstand the mechanical stretch of filling/voiding and the chemical irritation of concentrated urine.
No ATP → urothelial barrier thins → can't maintain tight junctions → concentrated urine irritates underlying tissue → urgency, frequency, susceptibility to UTIs.
The Full Picture
All Rapidly Dividing Cell Lines
| Tissue | Sign of failure | Mechanism |
|---|---|---|
| Skin | Dry, flaky, itchy | No ATP for collagen synthesis / DNA repair |
| Hair | Brittle, falls out | Follicle cells can't replace shaft |
| Nails | Dry, brittle, cracking | No new nail plate production |
| GI Tract | N/V/D, malabsorption | Active transport pumps offline |
| Respiratory | Recurrent bronchitis/PNA | Cilia stop → mucus stacks up |
| Renal (PCT) | Glucosuria, electrolyte loss | Reabsorption/secretion pumps fail |
| Uterus | Secondary amenorrhea, sterility | Endometrium can't proliferate monthly |
| Blood vessels | Vascular fragility, ↑ permeability | Endothelial cell replacement fails |
| Bladder | UTI susceptibility, irritation | Urothelial barrier thins |
Prove It
4 Patients Walked In
Don't kill them. Friendly stakes only.