Homeostatic processes control many of our bodily functions such as deep body temperature, arterial blood pressure, heart rate and blood sugar level, and they serve to provide our body cells with an environment in which they function optimally. Pressure is created by the heart pumping blood through the arteries. Downstream from the main arteries are smaller arteries that are surrounded by circular bands of muscle. The more these muscles contract, the greater the increase in arterial blood pressure because there is greater resistance to blood flow, just as you can increase the water pressure in a garden hose by squeezing the opening at the end.
Pressure is monitored by pressure sensors in the large arteries that carry blood to the brain.
Signals from these sensors are sent to the brain, which in turn controls the pumping activity of the heart and the degree of contraction of the muscles around the small arteries. These muscles are made to relax as the blood pressure exceeds the target level, and made to contract when it drops below the target level. Target levels vary as the need arises. Blood pressure is reduced during sleep, while during exercise it may double. This does not mean a deficiency, let alone a breakdown of the homeostatic mechanism, but simply that the target level has been reset, because the body's needs have changed.