Introduction

Introduction

Erectile dysfunction (impotence) is the inability to achieve or maintain an erection sufficiently rigid for sexual intercourse, ejaculation, or both. Sexual drive and the ability to have an orgasm are not necessarily affected. Because all men experience erection problems from time to time, doctors consider impotence to be present if attempts at intercourse fail on at least 25% of attempts.

Erectile dysfunction is not new in medicine or human experience, but it is not easily or openly discussed. Cultural expectations of male sexuality inhibit many men from seeking help for a disorder that can, in most cases, benefit from medical treatment. The term "impotence" comes from Latin and means loss of power; a more accurate term is "erectile dysfunction."

The Penis and Erectile Function

The Structure of the Penis. The penis is composed of the following structures:

• Two parallel columns of spongy tissue called the corpus cavernosa, or erectile bodies.
• A central spongy chamber called the corpus spongiosum, which contains the urethra, the tube that carries urine from the bladder through the penis.

These structures are made up of erectile tissue. Erectile tissue is rich in tiny pools of blood vessels called cavernous sinuses. Each of these vessels are surrounded by smooth muscles and supported by elastic fibrous tissue composed of a protein called collagen.

Erectile Function and Nitric Oxide. The penis is either flaccid or erect depending on the state of arousal. In the flaccid, or unerect, penis, the following normally occurs:

• Small arteries leading to the cavernous sinuses contract, reducing the inflow of blood.
• The smooth muscles regulating the many tiny blood vessels also stay contracted, limiting the amount of blood that can collect in the penis.

During arousal the following occurs:

• The man's central nervous system stimulates the release of a number of chemicals, including nitric oxide, which is now considered the main contributor for eliciting and maintaining erection.
• Nitric oxide stimulates production of cyclic GMP, a chemical that relaxes the smooth muscles in the penis. This allows blood to flow into the tiny pool-like cavernous sinuses, flooding the penis.
• This increased blood flow nearly doubles the diameter of the spongy chambers.
• The veins surrounding the chambers are squeezed almost completely shut by this pressure.
• The veins are unable to drain blood out of the penis and so the penis becomes rigid and erect.
• After ejaculation or arousal, cyclic GMP is broken down by an enzyme called phosphodiesterase-5 (PDE5), and other compounds are released that cause the penis to become flaccid (unerect) again.