ANS Control of Blood Flow
In the skeletal muscles, sympathetic input typically causes vasodilation, increasing blood flow. In contrast, sympathetic input typically causes constriction of splanchnic blood vessels serving the liver, G.I. tract, and renal system. This is a critical part of the “flight or flight: response, which prioritizes blood flow to the skeletal muscles.
In the skin, noradrenergic sympathetic nerves cause vasoconstriction and reduce blood flow (hence the pale skin associated with stress). However, in response to increased body temperature, either due to environmental heart or exercise, specialized cholinergic sympathetic fibers produce vasodilation of skin blood vessels and also stimulate sweating, thus facilitating evaporative heatless.