The Anatomy of the Penis

The penis is used for penetrative sexual activity and urination

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The human penis has a reproductive function and urinary function. It contains the urethra, which allows for the passage of urine. It also has erectile and ejaculatory functions which make it possible for males to engage in sexual intercourse. The penis consists of a number of parts of which the most obvious externally are the shaft, the glans (head), and the foreskin. Removal of the foreskin for religious and/or medical purposes is referred to as circumcision.


The penis is centrally located on the front aspect of the body at the base of the pelvis. The scrotum, containing the testes, lies below the penis, and is a separate structure.

There are several major structures of the penis:

  • The penile urethra runs through the center of the penis and up to the bladder. Urine is released through this tube. Ejaculate also is released from the urethra.
  • The prepuce, or foreskin, is a shroud of skin that covers the head of the penis. It is this skin that is removed during circumcision.
  • The glans, or head of the penis, is a mucosal surface in men who are uncircumcised. In men who are circumcised, the glans is made of dry, non-mucosal skin
  • The corpus cavernosa are two columns of tissue that run along the sides of the penis. When filled with blood, they lead to a penile erection. The corpus cavernosa are also sometimes referred to as erectile bodies
  • The corpus spongiosum is a third column of erectile tissue that encloses the urethra and ends at the glans. It lies along the underside of the penis.

All of the structures of the penis are well supplied by blood vessels. It is the flow of blood into, and out of, the penis that provides the erectile function. When there is blood trapped in the erectile bodies of the penis, it is firm enough for sexual penetration. When the blood drains, it returns to the flaccid state.

The shaft of the penis, which consists of the urethra, and the three erectile bodies, is wrapped in fascia and skin. At the base of the penis are the suspensory ligaments, which support its position on the pelvis.

A systematic review of penis size found that the average flaccid length of the unstretched penis is 9 centimeters (cm), or 3.5 inches. However, there is substantial variation in penis size, and penis length tends to be correlated with overall height.

Anatomical Variations of the Penis

Hypospadias is diagnosed when the opening of the urethra is on the base of the penis rather than at the tip. It is one of the most common congenital abnormalities in human males. Approximately a third of the time, hypospadias occur in the context of other congenital abnormalities. This may indicate that the child has a disorder of sexual differentiation. In general, surgical correction of hypospadias is recommended during infancy or early childhood; however, there are risks of long term complications.

Chordee refers to a congenital curvature of the penis, in other words, a penis that is curved from the time of birth. It is more common in boys with hypospadias, but it can also occur on its own. Between 4 percent and 10 percent of males without hypospadias experience some degree of penile curvature. That number may as be as high as 25 percent for males with hypospadias.

Congenital absence of the penis, or aphalia, is an extremely rare condition. It usually occurs in the context of other congenital abnormalities. Congenital absence of the foreskin, or prepuce, is also possible but similarly rare.

Micropenis is defined as a stretched penis length that is less than 2.5 standard deviations of the mean. It is thought to occur in 1.5 out of 10,000 male children in the United States. The size of the penis reflects the hormonal environment prior to birth. Diagnosis of micropenis in children may be associated with other differences of sexual differentiation. It is also commonly associated with functional or structural problems of the testes.

Trapped penis, or inconspicuous penis, is different from micropenis. This occurs when the penis appears smaller than it actually is. Trapped penis may be caused by issues with the foreskin, a thick pad of fat, or other conditions that keep the penis' length obscured.


The primary functions of the penis are sexual and urinary. The urinary function of the penis is achieved by the passage of the urethra from the bladder, through the penis, to the exterior of the body. Obstruction of urinary flow in older men may be caused by growth of the prostate putting pressure on the urethra.

The sexual function of the penis can be broken into two stages, erectile and ejaculatory. The erectile function of the penis is controlled by the flow of blood into and out of the three erectile bodies—two corpus cavernosa and the corpus spongiosum. As such, erectile function is strongly related to the health of the cardiovascular system. Medications for erectile function work by making it easier for the penile blood vessels to dilate and the penis to become and remain engorged.

Ejaculation occurs through the penis, but is not solely a function of the penis. First, the vas deferens contract to move sperm towards the base of the penis. At the same time, the prostate gland and seminal vesicles release the secretions that make the bulk of the volume of semen. Then, at the time of ejaculation, muscle contractions at the base of the penis force semen out of the tip of the penis. The flow of the semen is unidirectional, and is regulated by muscle contractions around the base of the urethra. If those muscle contractions are incomplete, a person may experience retrograde ejaculation, where ejaculatory fluids move backward into the prostate.

Associated Conditions

There are a number of medical conditions that can affect the penis. They can be broadly divided into the following categories: conditions that affect the foreskin, conditions that affect erectile function, infectious or inflammatory conditions, and malignancies.

Conditions Affecting the Foreskin

Men and boys who have a foreskin may experience problems with either retracting the foreskin from the head of the penis or where the foreskin gets stuck in the retracted position. The first condition, phimosis, is not an emergency, particularly before puberty. Many young men can not fully retract their foreskin until after puberty. However, paraphimosis, where the foreskin gets stuck in the retracted position is a medical emergency. This is because it is possible for the stuck foreskin to restrict blood supply to the head of the penis.

Conditions Affecting Erectile Function

Erectile dysfunction occurs when a person can not get, or maintain, an erection sufficient for sexual intercourse. Erectile dysfunction may be caused by medical reasons, including medications. It may also be the result of stress or relationship problems.

Peyronie's disease is a curvature of the penis that is not congenital, or present from the time of birth. Sometimes, Peyronie's disease is the result of an injury during sex. However, other times it is caused by inflammatory processes that are not well understood. If the symptoms of Peyronie's disease are severe, they can affect erectile function.

Priapism refers to an erection that lasts more than four hours. It is not always the result of sexual arousal, and it can be quite painful. Priapism occurs when blood becomes trapped in the penis and is unable to drain. Priapism is considered a medical emergency and should be treated immediately, to avoid the risk of permanent erectile dysfunction. It can occur in individuals of any age, and is more common in those with certain medical conditions, such as sickle cell disease.

Inflammatory or Infectious Conditions

The penis is a possible site of infection for many sexually transmitted diseases. The external skin of the penis is susceptible to infections such as herpes and human papillomavirus (HPV). The urethra is a possible site of infections by other conditions such as gonorrhea and chlamydia.

Balanitis refers to inflammation of the head of the penis (and sometimes the foreskin). It can be caused by sexually transmitted diseases. However, it can also be caused by auto-immune conditions and other forms of chronic inflammation.

Urethritis refers to inflammation or infection of the urethra. It is often, but not always, caused by a sexually transmitted infection.

Urethral stricture occurs when the urethra becomes narrowed, making it difficult to urinate. This may be the result of infection, inflammation, or other processes. Not all issues with urination are caused by issues with the urethra or penis. They may also be caused by the prostate and/or bladder.

Penile Malignancies

Penis cancer is very rare. However, it can be an aggressive form of cancer. It originates in the cells of the penis.

Urethral cancer is similarly rare. It originates in either the proximal or distal end of the urethra.


The type of tests used to diagnose conditions of the penis depend on the symptoms being diagnosed.

Testing for erectile dysfunction and/or Peyronie's disease often involves a sexual history. In addition, your doctor may order imaging of your penis. This may include either an ultrasound or magnetic resonance imaging (MRI). Penile imaging is often done while the penis is erect. To get an erection in the doctor's office, the doctor will usually use an injection that causes blood to flow into the penis. You may also be asked to use one of a number of methods to determine whether you are getting erections at night. This is referred to as nocturnal tumescence testing.

Issues with penile discharge, pain, or inflammation may require testing for sexually transmitted diseases or other infections. This can include urine tests. It may also include visual examination or urethral swabs. Biopsies may be used to identify any lumps or lesions. Blood tests may also be used to look for signs of infection or inflammation that affect penis health.

Issues with urination may requite you to undergo a voiding cystourethrogram or VCU. This involves an image being taken while you urinate. The VCU allows the doctor to identify any blockages or restrictions in your urinary stream. This test is more commonly used in children than adults. It is also more often used after surgery affecting the penile urethra, including phalloplasty.

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