**Reactive hyperaemia** is the transient increase in organ blood flow that occurs following a brief period of ischaemia. Following ischaemia there will be a shortage of oxygen and a build-up of metabolic waste.
**Active hyperaemia** also known as Functional hyperaemia, metabolic hyperemia is the increased blood flow that occurs when tissue is active. When cells within the body are active in one way or another, they use more oxygen and fuel, such as glucose or fatty acids, than when they are not. Increased metabolic processes create more metabolic waste. The byproducts of metabolism are vasodilators. (Vasodilating metabolites: CO2, H+, K+, lactate, adenosine) Local arterioles respond to metabolism by dilatating, allowing more blood to reach the tissue. This prevents deprivation of the tissue.