Vascular control mechanisms in penile erection: phylogeny and the inevitability of multiple and overlapping systems

A co-ordinated series of vascular events underlie the generation of a penile erection. The control and regulation of this simple event is, in fact, a complex of interactions occurring at multiple levels. Many of these individual pathways and responses have been studied extensively. The understanding of the necessity of the integration between the individual pathways into a complex of series and parallel coupled mechanisms provides a rationale for the development of a framework of multiple and overlapping systems. This paper sets out some of the principles of integrated and balanced control of vasodilation and vasoconstriction in the penis. In addition, the role of growth induction and regression and the importance of time as a factor in studying penile structure and function is discussed.