genitourinary disorders
Overview of Male Sexual Function and Dysfunction
Erection
Erection is a neurovascular response to certain psychologic and/or tactile stimuli. Higher cortical input and a sacral parasympathetic reflex arc mediate the erectile response. Neural output travels through the cavernous nerves, which traverse the posterolateral aspect of the prostate. Terminating in the penile vasculature, these nonadrenergic, noncholinergic nerves liberate nitric oxide, a gas. Nitric oxide diffuses into penile arterial smooth muscle cells, causing increased production of cyclic guanosine monophosphate (cGMP), which relaxes the arteries and allows more blood to flow through them and into the corpora cavernosa. As the corpora fill with blood, intracavernous pressure increases, which compresses surrounding venules, causing veno-occlusion and decreased venous outflow. The increased inflow of blood and decreased outflow further increase intracavernous pressure, contributing to erection. Many factors affect the ability to have an erection (see Erectile Dysfunction ). 