During exercise, which factor primarily causes vasodilation in active muscles?

During exercise, which factor primarily causes vasodilation in active muscles?

• A. Sympathetic nerves cause vasoconstriction in nonessential tissues
• B. Local metabolic factors cause vasodilation in active muscles
• C. Baroreceptors trigger systemic vasodilation
• D. Parasympathetic activity increases in muscles

Answer: (B)

During exercise, active muscles need more blood, so the main driver of vasodilation is local metabolic control. As muscles work harder, they produce metabolites such as carbon dioxide, hydrogen ions, adenosine, potassium, and lactate. These substances accumulate in the interstitial fluid and cause the smooth muscle of arterioles to relax, reducing resistance and increasing blood flow to the muscle—this is active hyperemia. Endothelial cells also release nitric oxide in response to these metabolites, further promoting dilation. While sympathetic activity redistributes blood by constricting vessels in nonworking tissues, and baroreceptors help regulate pressure, the dilation in active muscles mainly comes from these local metabolic factors. Parasympathetic influence does not drive skeletal muscle vasodilation in exercise.

During exercise, active muscles need more blood, so the main driver of vasodilation is local metabolic control. As muscles work harder, they produce metabolites such as carbon dioxide, hydrogen ions, adenosine, potassium, and lactate. These substances accumulate in the interstitial fluid and cause the smooth muscle of arterioles to relax, reducing resistance and increasing blood flow to the muscle—this is active hyperemia. Endothelial cells also release nitric oxide in response to these metabolites, further promoting dilation. While sympathetic activity redistributes blood by constricting vessels in nonworking tissues, and baroreceptors help regulate pressure, the dilation in active muscles mainly comes from these local metabolic factors. Parasympathetic influence does not drive skeletal muscle vasodilation in exercise.