Erectile Dysfunction – Normal Erection Process, Causes, Symptoms

What is Erectile Dysfunction?

Erectile dysfunction (ED), or impotence, is any difficulty or inability to attain an erection or maintain it for a period of time that allows for sexual activity. The term is often used quite cautiously by men but accounts for varying degrees of disturbances with the penile erection. It is extremely common in males over the age of 70 years but is still significantly prevalent in men over the age of 40 years. Erectile dysfunction is not a once off occurrence as men may sometimes have a problem achieving and maintaining an erection for any number of reasons without there being any underlying pathology. However, repeated episodes of dysfunction need to be investigated and treated accordingly.

About 80% of ED cases are due to physical causes and often related to underlying chronic conditions while 20% are related to psychological causes. Erectile dysfunction may be complete, mild or moderate indicating the degree of inability to achieve or sustain an erection. While reduced sexual desire is sometimes a feature of ED, a loss of libido and problems with orgasm (ejaculation) should be considered separately as different sexual health disorders. It may, however, co-exist with erectile dysfunction.

The Erection Process

In order to understand how ED develops, it is important to have a knowledge of the physiology of penile erections.

The first step for an erection is the appropriate stimulus – either physical or psychological. The greater the stimulation, the greater the degree of the erection. Impulses through the parasympathetic nerves from the sacral part of the spinal cord causes the release of nitric oxide and other chemicals like cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP). These chemicals relax the smooth muscle fibers of the arteries and erectile tissue of the corpus cavernosa in the penis.

Blood flow is therefore increased significantly and the tissue fills with blood. The venules that carry blood out of the erectile tissue is almost completely blocked thereby preventing the outflow of blood. Forceful contraction of the ischiocavernous muscles then compress the base of the corpus cavernosa. The pressure within the erectile tissue then increases significantly giving a complete and firm erection. Blood flow in and out of the penis ceases temporarily.

Upon removal of the arousal stimulus or completion of the sexual act, several changes occur that lead to normal blood circulation to the penis and the loss of the erection. The release of neurotransmitters from the parasympathetic nerves cease. Phosphodiesterase enzymes (PDEs) breakdown chemical messengers acting on smooth muscles of the penile erectile tissue and arteries. These enzymes are an important component in the modern treatment of erectile dysfunction. Sympathetic stimulation also facilities the termination of the erection. Blood flow in and out of the penis is then restored. The erectile tissue empties of blood and becomes flaccid – detumescence.

Causes of Erectile Dysfunction

Erectile dysfunction can therefore arise at any one of the multiple systems and processes involved in normal penile erections. This may stem from the central nervous system, peripheral nerves, blood flow and vessels and/or the hormones. The different mechanisms and possibly causative conditions of erectile dysfunction are listed below.

Blood and Blood Vessels

  • Atherosclerosis
  • Hypertension (high blood pressure)
  • Myocardial infarction (heart attack)
  • Peripheral vascular disease
  • Sickle cell anemia


  • Alzheimer’s disease
  • Epilepsy
  • Multiple sclerosis
  • Parkinson’s disease
  • Stroke


  • Diabetes mellitus
  • Kidney failure
  • Hypertension
  • Hyperlipidemia
  • Liver cirrhosis
  • Cancer

Hormones and Hormonal Disorders

  • Hypogonadism
  • Hyperthyroidism
  • Hypothyroidism
  • Diabetes mellitus

Medication and Substances

Many drugs can cause erectile dysfunction as a side effect. The most common of these drugs are :

  • Antihypertensives
  • Antidepressants
  • Antipsychotics
  • Antiulcer agents
  • 5-Alpha reductase inhibitors
  • Cholesterol-lowering agents

Alcohol misuse and narcotics may also contribute to erectile dysfunction. Both may also contribute to malnutrition as the user does not adhere to normal eating habits which can also contribute to ED.

Penile Disorders

Although penile disorders are uncommon, it tends to always result in some degree of sexual dysfunction. The most significant of these is Peyronie’s disease which is the formation of a hard plaque or lump in the penile tissue. It is most likely related to severe trauma of the penis.

A priaprism is a painful and persistent erection that lasts for more than 4 hours. This can damage the erectile tissue in the penis. It has various causes but the more common of these are the use of certain medications and sickle cell anemia.

A rare penile disorder is that known as epispadias where there is defect of the urethral opening present from birth in boys. It causes an abnormal curvature of the penis and can contribute to repeated urinary tract infections and kidney disorders as well as erectile dysfunction.


Trauma may not always be due to an injury like a fall or a blow to the area. It may also occur when treating certain diseases of the pelvis and perineum particularly with various treatments for prostate, bladder  and colorectal cancer. Injuries and surgery to the spinal cord and pelvis may also contribute to erectile dysfunction.

Lifestyle, Diet and Other Causes

  • A sedentary lifestyle, excessive alcohol consumption and cigarette smoking may all contribute to erectile dysfunction.
  • Among nutritional factors, malnutrition in general and zinc deficiency may be a factor in ED.
  • Respiratory disorders like chronic obstructive pulmonary disease (COPD) and sleep apnea.


Psychiatric conditions may not cause any physical abnormalities of the penile erectile tissue, the nerves and/or blood vessels supplying it. These conditions may include :

  • Depression
  • Performance anxiety
  • Post-traumatic stress disorder (PTSD)
  • Relationship problems

Signs and Symptoms of Erectile Dysfunction

The features of ED can sometimes be confusing to men. As mentioned, it is not a once off incident but occurs repeatedly. In erectile dysfunction, the erection is weak, incomplete or lost quickly before ejaculation. With some cases, an erection cannot be achieved at all.

This often leads to performance anxiety, depression and/or relationship problems which may exacerbate the condition even further. There may be reduced sexual desire but this should be differentiated from a loss in libido despite being able to have normal penile erections.

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