Eric Holland OMS-I · ex-software engineer

Learn / Metabolism / The test

Metabolic reasoning

Whole-map thinking. Each case is a chain of cause → effect that ends in the labs: why DKA has ketones and hyperglycemia, why a drinker goes hypoglycemic, why an infant with MCAD deficiency spills no ketones. Walk through the chain on the map, then order it yourself, answer the why questions, or diagnose from the labs.

Case
The big map. Highlighted boxes are the parts of metabolism the current step is about. Scroll sideways when zoomed.
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GlycogenGlycogenGlucoseGlucoseGalactoseGalactoseFructoseFructoseGlucose-6-phosphateGlucose-6-phosphateRibose-5-P + NADPHRibose-5-P + NADPHFructose-6-phosphateFructose-6-phosphateFructose-1,6-bisPFructose-1,6-bisPG3P / DHAPG3P / DHAPGlycerol (fat)Glycerol (fat)PhosphoenolpyruvatePhosphoenolpyruvatePyruvatePyruvateLactateLactateAlanine (amino acids)Alanine (amino acids)Acetyl-CoAAcetyl-CoAOxaloacetateOxaloacetateCitrateCitrateTCA cycle → NADH/FADH₂TCA cycle → NADH/FADH₂ETC → ATPETC → ATPFatty acidsFatty acidsTriacylglycerolTriacylglycerolKetone bodiesKetone bodiesCholesterolCholesterolEthanolEthanolGlycogenolysis (phosphorylase)Hexokinase / glucokinaseLeloir pathway (GALT)HMP shunt (G6PD)GlycolysisPFK-1 ★ / FBPase-1AldolaseFructokinase → aldolase B(bypasses PFK-1)Glycerol kinase (liver)Hormone-sensitive lipaseLower glycolysis (2 ATP, 2 NADH)Pyruvate kinaseALT (glucose-alanine cycle)LDH (anaerobic)PDH (irreversible; thiamine)ADH → ALDH (2 NADH)Pyruvate carboxylase (biotin; +acetyl-CoA)Citrate synthaseCitrate synthaseTCA cycleOXPHOSATP-citrate lyase → ACC → FAS(needs NADPH)Hormone-sensitive lipaseHMG-CoA synthase / lyase (liver)HMG-CoA reductase (cytosol)

Pulled from a house fire, still oxygenating

A 40-year-old woman rescued from a burning apartment (polyurethane furniture) is confused and hypotensive. Pulse oximetry and PaO₂ are normal, yet she is profoundly acidotic.

Lactate14 mmol/L↑↑
PaO₂normal
Mixed venous O₂↑abnormally high
pH7.05↓↓
Anion gap↑↑

Cyanide poisoning (Complex IV inhibition)

Oxygen is delivered but cannot be used: the ETC stops, NADH piles up, and every cell falls back on glycolysis → lactate.

Condition card: Cyanide poisoning →Pathway map →

  1. Cyanide binds Fe³⁺ in heme a₃ of cytochrome c oxidase (Complex IV) → electrons cannot be passed to O₂.
  2. …
  3. …
  4. …
  5. …
  6. …
  7. …

Pathways involved: Electron transport & OXPHOS, PDH & TCA cycle, Glycolysis. Drill them one at a time in Metabolic pathways.

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