Small Group 1 - Problem 6 Flashcards
Eleanor, aged 12, developed exercise intolerance during her childhood. She suffers from fatigue and painful cramps in her muscles when she tries to sprint or perform strenuous exercise. Nonetheless, she is able to keep up with her friends fairly well on long hikes and in usual play, and she appears to be normal in other respects. Although Eleanor experiences fatigue and muscle cramps after a spring, she sometimes gets a second wind, whereby exercise becomes more easily tolerated after 10 minutes
What types of enzyme deficiencies would explain Eleanor’s condition?
Enzymes involved with glycogen metabolism in muscle
What disease does she probably have?
GSD5: McArdle’s
What enzyme is deficient in McArdle’s Disease?
Glycogen phosphorylase
Why does strenuous exercise cause McArdle’s patients pain?
Muscle glycogen stores are not available to provide the glucose needed by the exercising muscle
There is an above normal increase in the plasma lactate levels by exercising muscles in McArdle’s disease - True or false?
False. The normal increase should result from glycolytic metabolism by the exercising muscle, but that does not occur.
Would Eleanor’s enzyme deficiency be present in the liver?
No because she has normal fasting glucose levels and is well otherwise
Why did lactate levels not increase after strenuous exercise?
Lactate levels would only increase if glucose were metabolized during intense exercise; because muscle glycogen can’t be metabolized to glucose, insufficient glucose is available to contribute to a rise in lactate at this time.
Why did Eleanor experience a “second wind”
Initial exercise triggers the breakdown of liver glycogen, which would make free glucose available for muscle metabolism. The glucose levels in the blood would decline as the patient began exercising, triggering a release of glucagon and epinephrine, which would cause the metabolism of hepatic glycogen and release of glucose into circulation
why would consuming sucrose before exercising improve exercise tolerance?
Sucrose is rapidly metabolized to its component sugars (glucose and fructose). This would mean high levels of plasma glucose would have been present at the time exercise took place
What is the potential downside or limitation of routine oral sucrose treatments ahead of exercise
The effect is short-lived, and repeat dosing could lead to weight gain, further reducing exercise tolerance. It may also inhibit use of fatty acids, which are an important energy source during exercise
