Autoregulation refers to local control of blood distribution (through vasodilation) in response to a tissue's changing metabolic needs. Which statement best describes this concept?

• A. Global nervous control of vessel tone
• B. Hormonal regulation by adrenal glands
• C. Local dilation only during exercise
• D. Local control of blood distribution in response to metabolic needs

Answer: (D)

Autoregulation is the tissue’s own way of tuning its blood supply to match how much it’s working. When a piece of tissue becomes more active, it produces byproducts—like CO2, hydrogen ions, adenosine, and other metabolites—that cause nearby arterioles to dilate. This local widening increases blood flow specifically to that tissue, delivering more oxygen and nutrients and helping wash away waste. Because this adjustment comes from the local vessels responding to the tissue’s own needs, it happens independently of brain signals or adrenal hormones and can occur both during exercise and at rest.

A key idea here is functional hyperemia—the flow increasing directly in response to metabolic demand. There’s also a myogenic aspect, where vessels react to pressure changes to keep blood flow stable, but the central feature described in the statement is the local, metabolic-demand–driven control of perfusion.

So the best description is local control of blood distribution in response to metabolic needs. Global nervous control or systemic hormonal regulation would involve broader, organism-wide signals, and limiting dilation to exercise doesn’t capture autoregulation’s broader, tissue-specific nature.