Penile erection is managed by two different mechanisms: The first one is reflex erection, which is achieved by directly touching the penile shaft. The second is psychogenic erection, which is achieved by erotic or emotional stimuli. The former uses the peripheral nerves and the lower parts of the spinal cord, whereas the latter uses the limbic system of the brain. In both conditions an intact neural system is required for a successful and complete erection. Stimulation of penile shaft by the nervous system leads to the secretion of nitric oxide (NO), which causes the relaxation of smooth muscles of corpora cavernosa (the main erectile tissue of penis), and subsequently penile erection. Additionally, adequate levels of testosterone (produced by the testes) and an intact pituitary gland are required for the development of a healthy erectile system. As can be understood from the mechanisms of a normal erection, impotence may develop due to hormonal deficiency, disorders of the neural system, lack of adequate penile blood supply or psychological problems. Restriction of blood flow can arise from impaired endothelial function due to the usual causes associated with coronary artery disease.

Source: National Institute of Diabetes and Digestive and Kidney Diseases

Erectile dysfunction is caused by physiological or psychological factors, or both.

About 80-90% of cases of ED are caused by physiological origin, which are further classified into vascular (related to blood flow) and non-vascular factors. It is estimated that 70%of ED cases may be attributable to vascular diseases alone.

Source: The National Institute of Diabetes and Digestive and Kidney Diseases

• Diabetes
• Hypertension
• High Blood Cholesterol
• Cardiac Diseases
• Smoking
• Prostatitis

Poor Overall Circulation

Type 2 Diabetes mellitus occurs when the pancreas does not make enough insulin, or when body tissues cannot utilize insulin effciently, resulting in an abnormally high blood glucose level.

Advancing thirst, tiredness, weight loss and blurred vision, etc. are symptoms of diabetes. The condition will also lead to erectile dysfunction by inducing damages of blood vessels and nerves involved in erection.

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Hypertension is a condition in which the blood pressure is persistently higher than normal (140/90 mmHg), even when you are resting or relaxed.

Smoking, physical inactivity, obesity, stress, excess alcohol intake and a family history of hypertension are risk factors of hypertension. Most people with hypertension do not have any symptoms. According to the Population Health Survey of the Department of Health, 60% of male with hypertension do not know they have the disease. Hypertension is usually diagnosed unexpectedly in a routine health check. When severe, hypertension will cause headache, dizziness, and visual problems. Impotence is also one of the symptoms of hypertension. It is because penile arteries are damaged by excessive blood pressure. Normally, these arteries dilate in response to sexual stimulation, allowing more blood to flow into the spongy tissue of the penis to produce an erection. The excessive pressure in these arteries may cause tiny tears, which are subsequently repaired by the body. The healed arteries have thicker walls to better resist the elevated blood pressure. These thicker blood vessel walls, though, will impose extra resistance to blood flow into the erectile tissues of the penis.

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Cardiac Disease is one of the main killer diseases among men in Hong Kong, causing 3,442 deaths in 2008. Coronary heart disease accounted for approximately two-thirds of all heart-disease-related deaths in men.

Coronary heart disease (CHD) is a type of heart disease due to the occlusion of the coronary arteries. The coronary arteries serve to supply oxygen and nutrients to the heart muscle. When the arteries become narrow and stiff because of fatty plaques, blood supply to the heart will be reduced and heart muscles will be damaged.

A number of risk factors, which may work independently or in combinations, can lead to coronary heart disease, including smoking, high-fat diet, physical inactivity, high blood pressure, high cholesterol levels, obesity, diabetes mellitus, stress and family history of coronary heart disease. The most common signs and symptoms are chest pain, puffiness and shortness of breath, paleness, weakness, vomiting or indigestion. Erectile dysfunction is one of the common symptoms since diseased penile blood vessels can lead to reduced blood flow to the organ.

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Smoking is associated with erectile dysfunction by damaging the blood circulation system in the penis. As ED is shown to be highly prevalent among smokers in clinical studies, it is hypothesized that quitting smoking can help prevent ED, and improve the condition in ED patients.

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Prostatitis is inflammation of the prostate gland. It can be sudden and acute, or reoccurring and chronic. This disease often is accompanied by a strong and frequent urge to urinate, difficulty urinating (dribbling or hesitant urinating that often results in only small amounts of urine), and/or by pain in the lower back or abdomen. Prostatitis can also cause erectile dysfunction due to the reduced blood flow.

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Other associated physical conditions or causes are less common. These include:

Neurogenic Disorders		Spinal cord and brain injuries, nerve disorders such as Parkinson's disease, Alzheimer's disease, multiple sclerosis, and stroke.
Hormonal Disorders		Pituitary gland tumor; low level of the hormone testosterone.
Cavernous Disorders		Peyronie's disease.
Metabolic Syndrome		Characterized by belly fat, high unhealthy cholesterol and triglyceride levels, high blood pressure, and insulin resistance.
Surgery		Radiation therapy, surgery of the colon, prostate, bladder, which may damage the nerves and blood vessels involved in erection.
Medication Caused		Various antihypertensives (medications intended to control high blood pressure) and some drugs that modify central nervous system response may inhibit erection by denying blood supply or by altering nerve activity.
Obesity		Men who are obese are much more likely to have erectile dysfunction than men with a normal weight.

Since erectile dysfunction can be an early symptom of such underlying medical conditions, it is essential for patients to seek prompt diagnosis and treatment.

It is however, not uncommon to see ED in an otherwise completely healthy person, both physically and psychologically. It is postulated that the penile circulation is intrinsically precarious, being an end-artery it may not be surprising that blood flow to the penis be partially occluded as men age. Although this may not cause major health problems, erection problems may arise due to the hindered penile blood flow.

Psychological factors are responsible for about 10%-20% of all cases of ED. It is often secondary to an underlying physical cause. In some cases, the psychological effects of ED may stem from childhood abuse or sexual trauma. However, the most common psychological causes of ED include:

Stress		Stress can be job-related, money-related, or the result of marital problems, among other factors.
Anxiety		Once a man experiences unsatisfactory erection, he may become overly worried that the problem will happen again. This can lead to "performance anxiety", or a fear of sexual failure, and consistently cause ED.
Guilt/Low self-esteem		A man may feel guilty that he is not satisfying his partner.
Depression		A common cause of ED, depression affects a person physically and psychologically. Depression can cause ED even when a man is completely comfortable in sexual situations. Drugs used to treat depression may also cause ED.
Indifference		This may come as a result of age and subsequent loss of interest in sex.

• Being able to achieve or maintain an erection with one partner but not with another.
• Having strong and lasting erections in the mornings and during masturbation but not during love making.
• Tendency to affect younger men with unstable relationships or unsettling past experiences.

Other Possibilities That Causes ED

A variety of risk factors can contribute to erectile dysfunction. They include:

Getting Older		As many as 80% of men aged 75 and older have erectile dysfunction. Erections may take longer to achieve, may not be as rigid or may take more direct touch to the penis to occur. But erectile dysfunction isn't an inevitable consequence of normal aging. Erectile dysfunction often occurs in older men mainly because they're more likely to have underlying health conditions or take medications that interfere with erectile function.
Substance Abuse		Chronic use of alcohol, marijuana or other drugs often causes erectile dysfunction and decreased sexual drive.
Prolonged Bicycling		Over an extended period, pressure from a bicycle seat has been shown to compress nerves and blood vessels supplying the penis, leading to temporary erectile dysfunction and penile numbness.