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.
Cramps at the start of exercise, then a second wind
A 19-year-old college hockey player gets painful cramps and weakness within minutes of intense exertion; after a short rest he can continue ('second wind'). Twice his urine has been dark after games.
| CK | ↑↑ after exercise | ↑ |
| Urine myoglobin | positive | ↑ |
| Blood glucose | normal | |
| Ischemic forearm test | no rise in lactate; ammonia rises | abnormal |
McArdle disease (GSD V, muscle glycogen phosphorylase)
Muscle can't tap its own glycogen for the first minutes of exercise; blood glucose and fatty acids arrive later — the second wind.
Condition card: McArdle disease (glycogen storage disease type V) →Pathway map →
- High-intensity exercise → Ca²⁺/calmodulin and AMP should switch muscle glycogen phosphorylase on within seconds.
- …
- …
- …
- …
- …
Pathways involved: Glycogen synthesis & breakdown, Glycolysis. Drill them one at a time in Metabolic pathways.