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Erectile dysfunction (ED), formerly known as impotence, is defined as the persistent inability to attain or maintain penile erection sufficiently for sexual intercourse.

The penis contains two chambers, called the corpora cavernosa which run the length of the organ. A spongy tissue fills the chambers and they are surrounded by a membrane called the tunica albuginea. The spongy tissue contains smooth muscles, fibrous tissues, spaces, veins, and arteries. The urethra, which is the channel for urine and ejaculate, runs along the underside of the corpora cavernosa.

Erection begins with both sensory and mental stimulation. Impulses from the brain and local nerves cause the muscles of the corpora cavernosa to relax, thereby, allowing blood to flow in and fill the open spaces. The blood creates pressure in the corpora cavernosa, making the penis expand. The tunica albuginea helps to trap the blood in the corpora cavernosa, thereby, sustaining erection. Erection is reversed when muscles in the penis contract, stopping the inflow of blood and opening outflow channels.

Adequate function and interaction of four major organ systems must occur for a man to experience a normal erection:

• Vascular system - supplies blood to the penis
• Nervous system - parasympathetic nerves called nervi erigentes convey impulses to the penis bringing about an erection
• Brain - responds to sexual stimulation by arousing the male to respond with an erection
• Endocrine system - abnormalities of the endocrine system (e.g., diabetes; hypogonadism) are recognized organic risk factors of ED

An estimated 10-20 million American men have some degree of erectile dysfunction. Although the incidence of ED increases steadily with age, it is not an inevitable consequence of aging. Erectile dysfunction affects only about 5% of men under age 40, whereas, it affects about 50% of American men between ages 40 to 70.