The blood supply of the penis is mainly derived from the pudendal artery (a branch of the internal iliac artery). The pudendal artery becomes the penile artery at the root of the penis. This artery then branches to give four main branches:
The most important of these arteries are the cavernosal arteries as they run down the centre of each corpus cavernosum and provide the main blood supply. The venous drainage occurs through a superficial, intermediate and deep system. The superficial system drains via the superficial dorsal vein into the pudendal branches of the saphenous vein. The other systems drain via the deep dorsal vein, crural and cavernosal veins into the internal iliac veins.
The penis is innervated by somatic and autonomic nerves. The somatic nerves supply the sensory fibres and the perineal motor fibres. The penis is innervated by both the parasympathetic and sympathetic nervous system. The parasympathetic innervation results in the formation of the erection, while the sympathetic innervation is involved in ejaculation.
The maintenance of an erection and the tone of the cavernosal smooth muscle are determined by an integrated response to neural stimulation and paracrine or autocrine systems.
Sympathetic noradrenergic fibres and parasympathetic cholinergic fibres innervate the cavernosal tissue. Both sets have opposing effects. In addition to these there are the non-adrenergic-non-cholinergic fibres (NANC).