Active hyperemia refers to which of the following?

• A. Increased blood flow to tissue due to metabolic activity
• B. Decreased blood flow due to obstruction
• C. Increased lymph production
• D. No autoregulation

Answer: (A)

Active hyperemia is the increase in blood flow to tissue that accompanies increased metabolic activity. When tissue metabolism rises, cells release vasodilatory metabolites such as CO2, lactic acid, adenosine, and nitric oxide. These local mediators dilate arterioles, lowering resistance and increasing perfusion to match the higher oxygen demand and help clear byproducts. This is a local autoregulatory response, driven by the tissue’s own needs.

The other options don’t fit: obstruction would reduce flow (ischemia), lymph production is not the driver, and lack of autoregulation would not explain the activity-driven increase in flow.