Notice that distribution to the brain does not change, while much more blood goes to the muscles and the skin at the expense of the kidneys and GI tract. A very important component which provides blood for this redistribution is the venous reservoir. The vasomotor center in the medulla of the brain is responsible for the overall control of blood distribution and pressure throughout the body. The baroreceptors allow maintenance of normal blood pressure. Autoregulation produces local control of blood flow to an organ or tissue area according to tissue needs.
Autoregulation is usually short-term and can enhance or override the vasomotor center.
In response to increasing pressure the small arteries and arterioles vasoconstrict, thus maintaining constant blood flow despite the increase in pressure. This results in the most blood directed to the most active muscles. Circulation to the heart can increase 3 to 4 times with exercise. The main mechanism responsible for this is myogenic autoregulation of cerebral arteries. In addition, the brain is very sensitive to carbon dioxide and the lowered pH it brings.