In the erect state, relaxation of the small Helisine arteries allows a rapid increase in blood inflow and exposure of the lacunar spaces (sinusoids) to systemic blood pressure . In the flaccid state, the small arterioles are contracted and restrict the arterial inflow into the lacunar spaces. These arteries are branches of the major blood supply to the pelvis and in turn branch into the deep penile artery that supplies the corpora cavernosa through small vessels known as Helisine arteries or arterioles . Blood supply to the penis originates from the right and left internal pudendal arteries. In addition, all three cylinders are covered by a second, less-dense sheath called Buck's fascia. The third cylinder, the corpus spongiosum, is outside the tunica albuginea and does not become rigid.

During an erection, one layer of the tunica albuginea stretches lengthways, which allows the penis to become longer, and the other layer stretches crosswise, which allows the penis to become thicker. Surrounding each of the corpora cavernosa is the tunica albuginea, a dense, multilayered, collagenous sheath that gives the penis flexibility, rigidity, and tissue strength. The spongy erectile tissue within the three cylinders consists of a mass of smooth muscle, often referred to as trabecular smooth muscle, within which is embedded a network of endotbelial-lined vascular spaces called sinusoids or lacunar spaces . These subtunical venules merge to form emissary venules that exit through the tunica albuginea and pass into the larger venous system, both deep and near the surface. The most important feature of the venous drainage system is that beneath the tunica albuginea a network of veins, the sinusoidal venules from the lacunar spaces, drains the erectile cylinders when the penis is flaccid. The third branch, the bulbourethral artery, supplies the corpus spongiosum. Another branch of the penile artery, the dorsal artery, supplies the glans and the penile skin.