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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.
Three days without food — the normal response
A healthy 30-year-old completes a 72-hour water-only fast for a religious observance. She feels tired but is alert, with mild ketone breath.
| Glucose | 62 mg/dL | low-normal |
| Insulin | ↓ | ↓ |
| Glucagon | ↑ | ↑ |
| β-Hydroxybutyrate | 3–5 mmol/L | ↑ |
| Free fatty acids | ↑ | ↑ |
| Urine nitrogen | falling by day 3 | ↓ |
Normal adaptation to prolonged fasting
Glycogen for a day, gluconeogenesis from muscle for two, then ketones take over so muscle protein is spared.
Condition card: Hypoglycemia in counter-regulatory hormone deficiency (glucagon, epinephrine/adrenal insufficiency, cortisol) →Pathway map →
- Hours 0–12: insulin falls, glucagon rises → hepatic glycogenolysis holds blood glucose.
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Pathways involved: Gluconeogenesis, Ketogenesis & ketone body use, Lipolysis, carnitine shuttle & β-oxidation, Glycogen synthesis & breakdown. Drill them one at a time in Metabolic pathways.