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==Active or Arterial Hyperaemia==
* Increased arterial blood inflow to an organ or tissue.
* Causes erythema.
* Results from active dilatation of arterioles and capillaries in association with autonomic nervous stimulus.
* May be:
** Physiological and transient.
** Pathological and sustained.
*** Usually associated with inflammation.
**** The classic example being the weal reaction in man or "blistering" in animals.
*** May also occur where there is:
**** Exaggerated localised raised temperature.
**** Generalised pyrexia.
**** The presence of toxins.
==Reaction hyperaemia==
* May follow restoration of blood flow after a short-term occlusion.
** For example, after a tourniquet or ligature is removed.
* Vessels dilate, as a result of local release of vaso-active substances.
** There is also possibly a neurogenic component involved.
[[Category:Circulatory Disorders - Pathology]]