Hyperemia

Hyperemia describes the increase of blood flow to different tissues in the body. It can have medical implications, but is also a regulatory response, allowing change in blood supply to different tissues through vasodilation.

Hyperemia and the regulation of blood flow
Functional hyperemia is an increase in blood flow to a tissue due to the presence of metabolites and a change in general conditions. When a tissue increases activity there is a well characterized fall in the partial pressure of oxygen and pH, an increase in partial pressure of carbon dioxide, and a rise in temperature and the concentration of potassium ions. The mechanism for vasodilation is unclear, but it may have something to do with the opening of precapillary sphincters.

Active hyperemia is also a term used to describe dilation of arteriolar smooth muscle to increase blood flow in response to an increase in metabolism. Reactive hyperemia is the same but in response to a profound increase in blood flow to an organ after being occluded. There will be a shortage of oxygen and a build-up of metabolic waste.