Erectile Dysfunction (ED), once known simply as impotence, is the inability to achieve or sustain penile erection. But that definition partially obscures that fact that ED comes in different types and degrees.

Nearly every male old enough to have had an erect penis will be unable to do so when desired at some time in his life. When the event is isolated, it may not deserve the name of an intimidating sounding condition. Whether due to occasional excess alcohol consumption, anxiety about work or sexual performance, or for any other reason, the lack of a stiffened penis doesn't by itself call for medical attention.

It's only when the situation is chronic or long-lived that men will generally need to seek out professional advice, and only if erection is needed for sex or peace of mind. Sex is a healthy and desirable part of life but there are periods in the lives of many men when not achieving an erection is simply not a problem.

When it is a problem, it is one that usually comes in degrees. Because of the underlying physiology, coupled with external circumstances, a penis may be maximally erect, partly erect or limp. In many cases, partly erect may be sufficient to satisfy the man alone or him and his sexual partner.

That underlying physiology, in broad outline, is fairly simple.

The penis is similar to a series of concentric cylinders or tubes, filled with small chambers and other tubes. One major cylinder is called the corpora cavernosa. Spongy tissues line the cylinder. The spongy tissue is composed of smooth muscle fibers, blood vessels (veins and arteries) and fluids.

Under usual circumstances, stimulation causes several times the resting amount of blood to flow. It moves to fill the space and engorge the muscles. The resulting fluid pressure causes the penis to elongate and stiffen. The result is an erection.

Because those relatively simple systems in turn rely on an enormously complex set of nerves, hormones, circulatory and other body functions, there are a corresponding set of things that can go wrong. Blood pressure changes, inability of nerves to send signals properly, failed muscle stimulation and many other circumstances are possible. Those in turn have their own dependencies and possible failures.

Equally important are the psychological features of the human male that have to function in a certain way for an erection to occur. Stimulation is partly physical, a function of the nerves, particularly those located in and around the penis. But stimulation is also a function of the limbic system, the part of the brain associated with emotions. Even when there is no obvious physical defect, the limbic system and the mind are heavily invested in imagery, fantasy, expectation and other psychological aspects of sex.

Those psychological features, while harder to objectively observe and measure, can go astray. Depression, anxiety, self-deception and other issues can cause failure of erection for extended periods or in multiple sexual encounters.

Fortunately, whether the underlying issues are psychological or physiological or a combination of the two, there are multiple effective treatments available for erectile dysfunction.