Impotence is a disorder of the male reproductive system and is the inability to maintain an erection of the penis. An erection is dependent on blood flow to the penis, which is triggered by sensory and mental stimulation. With appropriate stimulation, arterial blood flows into the small arteries inside the penis. As the blood vessels in the penis dilate, blood flow increases, and vascular channels called the corpora cavernosa and the corpora spongeosum become engorged, resulting in an erection. Impotence can be caused by a disruption at any stage in this series of events. Certain diseases, including diabetes and muscular dystrophy can cause impotence. Psychological factors can also lead to impotence. And, impotence can be a side effect of some common medications.