Functional hyperemia

Hyperemia is 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. Clinically, hyperaemia in tissues manifest as erythema (redness of the skin) because of the engorgement of vessels with oxygenated blood. Hyperaemia can also occur due to a fall in atmospheric pressure outside the body. The term is from Greek ὑπέρ (hupér, 'over') + αἷμα (haîma, “blood”).Functional hyperaemia 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 mechanisms of vasodilation are predominantly local metabolites and myogenic effects. Increased metabolic activity of the tissue leads to a local increase in the extracellular concentration of such chemicals as adenosine, carbon dioxide, and lactic acid, and a decrease in oxygen and pH. These changes cause significant vasodilation. The reverse occurs when metabolic activity is slowed and these substances wash out of the tissues. The myogenic effect refers to the inherent attempt of vascular smooth muscle surrounding arterioles and arteries to maintain the tension in the wall of these blood vessels by dilating when internal pressure is reduced and to constrict when wall tension increases.Functional hyperaemia, metabolic hyperemia, arterial hyperemia or active hyperaemia, is the increased blood flow that occurs when tissue is active.Reactive hyperaemia, a sub-category of arterial hyperemia, 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.