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.
Vomiting and hypoglycemia after the first fruit
A 6-month-old was thriving on breast milk and formula. Two weeks after starting fruit purées and juice she has vomiting, lethargy, sweating and irritability after meals, with jaundice and an enlarged liver.
| Glucose (post-prandial) | 38 mg/dL | ↓ |
| Urine reducing substances | positive | + |
| Urine glucose oxidase | negative | |
| AST/ALT, bilirubin | ↑ | ↑ |
| Phosphate | ↓ | ↓ |
| Uric acid | ↑ | ↑ |
Hereditary fructose intolerance (aldolase B deficiency)
Fructose-1-phosphate traps the liver's phosphate; without Pi there is no ATP, and without ATP neither glycogenolysis nor gluconeogenesis can run.
Condition card: Hereditary fructose intolerance (secondary hyperuricemia) →Pathway map →
- Sucrose/fruit fructose → GLUT-5 → portal blood → liver takes 90% on first pass.
- …
- …
- …
- …
- …
- …
Pathways involved: Fructose metabolism, Glycogen synthesis & breakdown, Gluconeogenesis. Drill them one at a time in Metabolic pathways.