Practice Test 8

A subject is given a bolus of insulin and then performs light activity. Plasma glucose falls, but muscle glucose uptake increases. The investigator notes that insulin’s effect on muscle is amplified when muscle contraction is present, even without further increases in insulin. Which explanation best accounts for the increased muscle glucose uptake during contraction?

An endurance athlete performs a 2-hour run without carbohydrate intake. Plasma glucose remains near 4.5 mM, but plasma ketones rise from 0.2 to 0.8 mM. The investigator notes that both glucagon and epinephrine are elevated. Which integrated change best supports ketone production during prolonged exercise?