Anatomically, the human penis consists of three major structures: the urethra, and two erectile bodies. The purpose of the urethra is to conduct urine. The urethra ends at the tip of the glans of the penis, and the glans is formed from a thick, spongy cylinder that surrounds the urethra. The erectile bodies are two long cylinders located next to each other inside the penis. They are situated above, and parallel to, the urethra; they are covered with fascia (Buck’s fascia); and they contain blood. During erection, the amount of blood inside the cylinders increases. While inflow increases, outflow decreases, and the cylinders are filled to the limit with blood. As a result, they stand upright, causing erection of the penis.
Erectile Dysfunction, or impotence, is the chronic inability to achieve or maintain an erection that is firm enough for vaginal penetration or sexual intercourse. The word "impotence" may also be used to describe other problems that interfere with sexual intercourse and reproduction, such as lack of sexual desire.
In older men, ED usually has a physical cause, such as disease, injury, or as a side effect of drugs. Any disorder that causes injury to the nerves, or that impairs blood flow in the penis, can cause ED. The incidence of ED increases with age. About 5% of 40-year-old men, and 15% to 25% of 65-year-old men, experience ED.
The most common cause of ED is damage to nerves, arteries, smooth muscles, and fibrous tissues, often as a result of disease. Diseases such as diabetes, kidney disease, chronic alcoholism, multiple sclerosis, atherosclerosis, vascular disease, and neurological disease account for about 70% of ED cases. Between 35% and 50% of men with diabetes experience ED.