The dilating of blood vessels brought on by activation of the parasympathetic division of the autonomic nervous system. Vasodilatation is one component of mammalian thermoregulation; in response to excessive heat, warm blood flows to the body's surface and results in heat loss by radiation.

widening of the blood vessels.

Dilatation of blood vessel due to relaxation of smooth muscle in wall. Can be evoked by neural activity or chemical agents acting in hormonal or local fashion from epithelium, for example nitric oxide. Can be evoked by reduction in number of impulses in vasoconstrictor fibres. Flow to tissue is increased.