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Medical Author:

Dennis Lee, MD

Dennis Lee, MD

Dr. Lee was born in Shanghai, China, and received his college and medical training in the United States. He is fluent in English and three Chinese dialects. He graduated with chemistry departmental honors from Harvey Mudd College. He was appointed president of AOA society at UCLA School of Medicine. He underwent internal medicine residency and gastroenterology fellowship training at Cedars Sinai Medical Center.

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Medical Author:

Siamak T. Nabili, MD, MPH

Siamak T. Nabili, MD, MPH

Dr. Nabili received his undergraduate degree from the University of California, San Diego (UCSD), majoring in chemistry and biochemistry. He then completed his graduate degree at the University of California, Los Angeles (UCLA). His graduate training included a specialized fellowship in public health where his research focused on environmental health and health-care delivery and management.

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Medical Editor:

Jay W. Marks, MD

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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Medical Editor:

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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In this Article

• What is erectile dysfunction?
• How common is erectile dysfunction?
• What is normal penis anatomy?
• How does erection occur?
• How is erection sustained?
• What are some of the risk factors for erectile dysfunction?
• What are the causes of erectile dysfunction?
• How is erectile dysfunction diagnosed?
• What are the treatments for erectile dysfunction?
• What medications are used to treat erectile dysfunction?
• Oral phosphodiesterase type 5 (PDE5) inhibitors
• Sildenafil (Viagra)
• Vardenafil (Levitra)
• Tadalafil (Cialis)
• Intracavernosal injections
• Intraurethral suppositories
• How effective is testosterone in treating erectile dysfunction?
• Can low testosterone level be replaced?
• Vacuum devices
• Surgery for erectile dysfunction
• What will the future bring for erectile dysfunction?
• Erectile Dysfunction At A Glance
• Impotence (Erectile Dysfunction, ED) FAQs
• Patient Comments: Erectile Dysfunction (Impotence) - Treatments
• Patient Comments: Erectile Dysfunction (Impotence) - Share Your Experience
• Find a local Urologist in your town
• Impotence (ED) Index

The penis contains two chambers, called the corpora cavernosa, which run the length of the upper side of the penis (see figure 1 below). The urethra, which is the channel for urine and ejaculate, runs along the underside of the corpora cavernosa. Filling the corpora cavernosa is a spongy tissue consisting of smooth muscles, fibrous tissues, spaces, veins, and arteries. A membrane, called the tunica albuginea, surrounds the corpora cavernosa. Veins located in the tunica albuginea drain blood out of the penis.

Erection begins with sexual stimulation. Sexual stimulation can be tactile (for example, by touching the penis) or mental (for example, by having sexual fantasies). Sexual stimulation or sexual arousal generates electrical impulses along the nerves going to the penis and causes the nerves to release nitric oxide, which in turn increases the production of cyclic GMP (cGMP) in the smooth muscle cells of the corpora cavernosa. The cGMP causes the smooth muscles of the corpora cavernosa to relax and allow rapid blood flow into the penis. The incoming blood fills the corpora cavernosa, making the penis expand.

The pressure from the expanding penis compresses the veins (blood vessels that drain the blood out of the penis) in the tunica albuginea, helping to trap the blood in the corpora cavernosa, thereby sustaining erection. Erection is reversed when cGMP levels in the corpora cavernosa fall, causing the smooth muscles of the corpora cavernosa to contract, stopping the inflow of blood and opening veins that drain blood away from the penis. The levels of the cGMP in the corpora cavernosa fall because it is destroyed by an enzyme called phosphodiesterase type 5 (PDE5).