Impotence (ED) (cont.)
How does erection occur?
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 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 in-coming blood fills
the corpora cavernosa, making the penis expand.
How is erection sustained?
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)
What are the causes of erectile dysfunction?
The ability to achieve and sustain erections require:
- A healthy nervous system that conducts nerve impulses
in the brain, spinal column, and penis,
- Healthy arteries in and near the corpora cavernosa,
- Healthy smooth muscles and fibrous tissues within the
corpora cavernosa, and
- Adequate levels of nitric oxide in the penis.
Erectile dysfunction can occur if one or more of these requirements are not
met. The causes of erectile dysfunction include:
- Aging: There are two reasons why older men are more likely to experience
erectile dysfunction than younger men. First, older men are more likely to
develop diseases (such as heart attacks, angina, strokes, diabetes mellitus, and
high blood pressure) that are associated with erectile dysfunction. Second, the
aging process alone can cause erectile dysfunction in some men; primarily by
decreasing the compliance of the tissues in the corpora cavernosa, although it
has been suggested, but not proven, that there is also decreased production of
nitric oxide in the nerves that innervate the corporal smooth muscle within the
penis.
- Diabetes mellitus: Erectile dysfunction tends to develop 10-15 years
earlier in diabetic men than among nondiabetic men. In a population study of men
with type I diabetes for more than 10 years, erectile dysfunction was reported
by 55% of men between the ages of 50 to 60 years. The increased risk of erectile
dysfunction among men with diabetes mellitus may be due to the earlier onset and
greater severity of atherosclerosis that narrows the arteries and thereby
reduces the delivery of blood to the penis. When insufficient blood is delivered
to the penis, it is not possible to achieve an erection.
Diabetes mellitus also
causes erectile dysfunction by damaging both sensory and autonomic nerves, a
condition called diabetic neuropathy. Smoking cigarettes, obesity, poor control
of blood glucose levels, and having diabetes mellitus for a long time further
increases the risk of erectile dysfunction in diabetes. In addition to atherosclerosis
and/or neuropathy causing ED in diabetes, many diabetic men develop a myopathy
(muscle disease) as their cause of ED in which the compliance of the muscle in
the corpora cavernosa is decreased and clinically this presents as an inability
to maintain the erection. For additional information, please read the Diabetes article.
- Hypertension (high blood pressure): Patients with essential hypertension
or arteriosclerosis have an increased risk of developing erectile dysfunction.
Essential hypertension is the most common form of hypertension; it is called
essential hypertension because it is not caused by another disease, (for
example, by kidney disease). It is not clearly known how essential hypertension
causes erectile dysfunction; however, patients with essential hypertension have
been found to have low production of nitric oxide by the arteries of the body,
including the arteries in the penis. Scientists now suspect that the decreased
levels of nitric oxide in patients with essential hypertension may contribute to
erectile dysfunction. For more information, please read the High Blood Pressure article.
- Cardiovascular diseases: The most common cause of cardiovascular diseases
in the United States is atherosclerosis, the narrowing and hardening of arteries
that reduces blood flow. Atherosclerosis typically affects arteries
throughout the body and is aggravated by hypertension, high blood cholesterol
levels, cigarette smoking, and diabetes mellitus. When coronary arteries
(arteries that supply blood to the heart muscle) are narrowed by
atherosclerosis, heart attacks and angina occur. When cerebral arteries
(arteries that supply blood to the brain) are narrowed by atherosclerosis,
strokes occur. Similarly, when arteries to the penis and the pelvic organs are
narrowed by atherosclerosis, insufficient blood is delivered to the penis to
achieve an erection. There is a close correlation between the severity of
atherosclerosis in the coronary arteries and erectile dysfunction. For example,
men with more severe coronary artery atherosclerosis also tend to have more
erectile dysfunction than men with mild or no coronary artery atherosclerosis.
Some doctors suggest that men with new onset erectile dysfunction should be
evaluated for silent coronary artery diseases (advanced coronary artery
atherosclerosis that has not yet caused angina or heart attacks). For more information,
please read the Heart Attack Prevention article.
- Cigarette smoking: Cigarette smoking aggravates atherosclerosis and
thereby increases the risk for erectile dysfunction. For more information, please read the
Smoking and Quitting Smoking article.
- Nerve or spinal cord damage: Damage to the spinal cord and nerves in the
pelvis can cause erectile dysfunction. Nerve damage can be due to disease,
trauma, or surgical procedures. Examples include injury to the spinal cord from
automobile accidents, injury to the pelvic nerves from prostate surgery,
multiple sclerosis (a neurological disease with the potential to cause
widespread damage to nerves), and long-term diabetes mellitus.
- Substance abuse: Marijuana, heroin, cocaine, and alcohol abuse contribute
to erectile dysfunction. Alcoholism, in addition to causing nerve damage, can
lead to atrophy of the testicles and lower testosterone levels. For more information, please visit the Drug Abuse Center.
- Low testosterone levels: Testosterone (the primary sex hormone in men) is
not only necessary for sex drive (libido) but also is necessary to maintain
nitric oxide levels in the penis. Therefore, men with hypogonadism (diminished
function of the testes resulting in low testosterone production) can have low
sex drive and erectile dysfunction.
- Medications: Many common medicines produce erectile dysfunction as a side
effect. Medicines that can cause erectile dysfunction include many used to treat
high blood pressure, antihistamines, antidepressants, tranquilizers, and
appetite suppressants. Examples of common medicines that can cause erectile
dysfunction include beta-blockers such as propranolol (Inderal),
hydrochlorothiazide, digoxin (Lanoxin), amitriptyline (Elavil), famotidine
(Pepcid), cimetidine (Tagamet), metoclopramide (Reglan), indomethacin (Indocin),
lithium (Eskalith; Lithobid), verapamil (Calan, Verelan, Isoptin), phenytoin
(Dilantin), and gemfibrozil (Lopid). For more, please visit the Medications Index.
- Depression and anxiety: Psychological factors may be responsible for
erectile dysfunction. These factors include stress, anxiety, guilt, depression,
low self-esteem, and fear of sexual failure. For more information, please visit the
Depression Center.
Next: How is erectile dysfunction diagnosed? »
- tadalafil, Cialis - Deciphers the medication tadalafil (Cialis), a drug used for the treatment of impotence.
- Penis Pump - Learn about penis pumps (vacuum constriction devices) for the treatment of erectile dysfunction (ED) or impotence. Pumps help a man maintain an erection.
- Diabetes - Learn about type 1 and 2 diabetes (Diabetes Mellitus) symptoms including increased urination, thirst, weight loss, fatigue, nausea, vomiting, skin infections, and blurred vision. Causes and diagnosis information is provided in the information.
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