Figure 24

Figure 24 Hemodynamics of flaccidity. (a) Tonic contraction of the walls of the helicine arteries and trabeculae allows only relatively small amounts of blood into the lacunar spaces. Whatever blood is entering is drained through the walls of the tunica albuginea by subtunical vessels. (b) Cross-section of penis: the box indicates the area shown enlarged in (a) and (c). (c) Hemodynamics of erection: dilatation of the helicine arteries and relaxation of the trabeculae allow the lacunar spaces to fill. Their engorgement compresses the obliquely oriented subtunical veins against the tunica albuginea. This veno-occlusive mechanism prevents venous leakage and facilitates the development of a full and rigid erection