Blood flow through most organs in the systemic circuit is regulated primarily by increasing or decreasing the sympathetic activity to arterioral smooth muscles in the organ. Another form of regulation called active hyperemia, depends upon the ,metabolic activity of the organ. Increased activity leads to increased interstitial fluid metabolites, which cause dilation of the arterioles, the former is a type of extrinsic regulation of blood flow; the latter is an example of intrinsic regulation.
