Autoregulation is a process within many biological systems, resulting from an internal adaptive mechanism that works to adjust (or mitigate) that system's response to stimuli. While most systems of the body show some degree of autoregulation, it is most clearly observed in the kidney, the heart, and the brain. Perfusion of these organs (especially the latter two) is essential for life, and through autoregulation the body can divert blood (and thus, oxygen) where it is most needed.
Read more about Autoregulation: Cerebral Autoregulation, Homeometric Autoregulation, Coronary Circulatory Autoregulation, Renal Autoregulation, Autoregulation of Genes