Schematic representation of the cutaneous vascular system in human glabrous skin

The arterial supply system branches to an AVA and also to nutritional capillary loops. In response to body cooling, there is increased activity of sympathetic nerves, which release norepinephrine to cause constriction predominantly of the AVA structures by activating alpha-2-adrenergic receptors located on the smooth muscle cells. AVAs appear to have increased activity of this constrictor mechanism, whereas nutritional blood flow through capillary loops is protected from sympathetic constriction and is therefore maintained. Local cooling amplifies sympathetic alpha-2-adrenergic receptor-dependent constriction of AVAs.