Innervation of the microcirculation

Neurogenic control of the peripheral circulation is accomplished by alterations in nerve discharge to the pre- and postcapillary vascular network in the various organs. The postganglionic sympathetic adrenergic nerves constitute the most important efferent pathway for neural control. The physiologic response of the microvasculature to neural influences depends on a number of factors: the pattern of distribution of the innervation to the microvessels is one of the more important determinants. In addition to its influence on the contractile state of vascular smooth muscle, the adrenergic nerves also have a trophic influence on the smooth muscle cells. Following surgical denervation of a vascular bed, the adrenergic nerve terminals degenerate, and subsequently reinnervate, the vasculature. During the period following denervation, a number of functional and morphologic changes occur in the smooth muscle. This review emphasizes those aspects of the structure and function of adrenergic nerves that may have particular relevance for microsurgery.