How does a successful erection work?

An erection begins with sensory and mental stimulation.

Impulses from the brain travelling down the spinal column and impulses from the nerves in the penis relax smooth muscles in two spongy cylinders that run the length of the penis, parallel to the urethra (the conduit for urine and semen).

When the impulses cause the muscles to relax, blood flows into spaces in the spongy tissue and this pressure makes the penis swell.  A membrane surrounding the cylinders helps to trap the blood in the penis and maintain the erection.

The penis returns to its flaccid state if the muscles contract, stopping the inflow of blood and opening outflow channels.
An erection problem can occur if any of the events in this sequence are disrupted. The problem may involve mental processes, nerve impulses or responses in muscles, fibrous tissue as well as veins and arteries in the penis.

Physical causes
The most common cause of erectile dysfunction is damage to arteries, smooth muscles and fibrous tissues.
•    Problems with the blood vessels (vascular problems) make up 48% of erection problems.
•    Problems with the nerves (neurological problems): 14%
•    Problems with the structure of the penis or surrounding tissues: 3%

These problems can in turn be caused by a variety of factors:
•    These may include diabetes, kidney disease and multiple sclerosis. Atherosclerosis or "hardening of the arteries" can prevent adequate blood from entering the penis.
•    Injury to the penis, spinal cord, prostate, bladder or pelvis: such injury can be the result of sports or car accidents, or even riding on hard bicycle seats (this is almost always temporary).
•    Complications of surgery or radiation (e.g. for prostate cancer), which can interfere with nerve impulses or blood flow to the penis. When the nervous system cannot transmit arousal signals, or when the blood vessels in the penis cannot fill or stay filled with blood, you are unable to have an erection.
•    Side effects of common medication: these include drugs taken for high blood pressure, anti-depressants, anti-histamines, tranquillisers, appetite suppressants and the ulcer drug cimetidine.
•    Substance abuse: chronic use of alcohol, marijuana or other drugs often causes impotence, which may be aggravated by decreased sexual drive. Excessive tobacco use can also block penile arteries.
•    Hormonal factors, such as low testosterone levels.
•    Erection problems in men over the age of 50 are more likely to have physical causes.

Psychological causes
Psychological problems, such as anxiety, interfere with the erection process by distracting the man from things that would normally arouse him.

These problems cause between 10 and 40% of erectile dysfunction. Even in cases where the underlying problem is physical, these factors can play an important secondary role, for example when a man who has had some erectile difficulty starts to anticipate and fear sexual failure.

As a result, psychological factors play some causal role in at least 80% of cases of erectile dysfunction.

Dependent on age, the psychological component is more significant in young and heathy men, compared to older men and those with significant co morbid disease.

These factors include:
•    Depression: erectile dysfunction is twice as likely among men suffering from depression as it is among those without depressive symptoms.
•    Relationship problems: a man who loses sexual interest in or desire for a particular partner may develop erection problems.
•    Anxiety and stress, including those caused by major life changes.
•    Grief and other reactions to major loss: recently widowed men may have erection problems.
•    Low self-esteem.
•    Guilt because of extramarital affairs, especially if sexually transmitted diseases are feared.
•    Psychological causes – more prominent in younger men.

Reviewed by Dr Dave Bowden MBBCh (Wits), FCS (SA) Urol. Specialist Urologist in private practice, Christiaan Barnard Memorial Hospital, Cape Town.

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