The Anatomy of the Penis

A complex organ used for urination, sex, and reproduction

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The penis is a complex external organ in males used to urinate and for sex and reproduction. It consists of several parts, including the shaft, head, and foreskin. A passage called the urethra runs through the center of the shaft and allows for the passage of urine and the ejaculation of semen. The shaft contains spongy columns of tissue that fill with blood to achieve an erection.

This article describes the anatomy and function of the penis as well as conditions that can affect the function or appearance of the penis at birth or later in life.


The penis is centrally located at the front of the body at the base of the pelvis. The scrotum, containing the testicles, lies below the penis.

The penis consists of several major structures:

  • Glans: The glans, or head of the penis, is the sensitive bulbous structure at the end of the corpus (shaft).
  • Urethra: The urethra is a tube that runs from the bladder to the head of the penis used for urination. It also crosses through the prostate gland where an opening, called the ejaculatory duct, receives sperm and ejaculatory fluid that make up semen.
  • Meatus: The meatus is the opening at the tip of the glans through which urine or semen exits the body.
  • Prepuce: The prepuce, or foreskin, is a loose fold of skin that covers the head of the penis. The removal of the foreskin is referred to as circumcision.
  • Corpus cavernosa: The corpus cavernosa are two columns of spongy tissue that run along the interior shaft of the penis. When filled with blood, the tissues stiffen, causing an erection.
  • Corpus spongiosum: The corpus spongiosum is the third column of tissue that prevents the urethra from closing during an erection.

The penis is well supplied by blood vessels. The shaft, which contains the urethra and three columns of erectile tissue, is wrapped in a band of connective tissue called the fascia and covered with skin. The base of the penis is supported by connective tissues, called suspensory ligaments, that hold the penis close to the pelvic bone

The average flaccid ("soft") length of a penis is 3.5 inches. The average length of an erect penis is 6 inches with an average circumference of 5 inches


The penis is made up of the corpus (shaft), glans (head), and prepuce (foreskin). The urethra is a tube through which urine or semen exits the body. The spongy columns of tissue within the shaft can fill with blood and cause an erection.


The primary functions of the penis are urinary and sexual. The sexual function of the penis can be further broken down into two stages: erection and ejaculation.


Urination is the expulsion of urine from the body. This occurs when urine passes from the bladder through the urethra to the meatus. The urine is propelled from the body by the contraction of the detrusor muscle in the wall of the bladder.

At the root of the penis is the external sphincter muscle which males can voluntarily flex to "pump" excess urine from the body and ensure the bladder is empty.


An erection is the stiffening of the penis caused by sexual arousal and/or physical stimulation. It is also normal for erections to occur during sleep and upon waking. An erection occurs when there is an increased flow of blood into the corpus cavernosa and corpus spongiosum.

During an erection, arteries servicing the erectile tissues will dilate (widen), causing the penis to engorge with blood. The engorgement simultaneously compresses the veins through which blood usually exits the penis. This "traps" the blood and helps sustain the erection.


Ejaculation is the discharge of semen from the body. It is usually accompanied by a sexual response called an orgasm.

Ejaculation involves a series of simultaneous, involuntary muscle contractions:

  • Firstly, a tube called the vas deferens contracts, propelling sperm from the testicles to the ejaculatory duct.
  • At the same time, the prostate gland and seminal vesicles contract, adding fluids that make up the main volume of semen.
  • At the same time, rapid contraction of muscles at the base of the penis, called periurethral muscles, propel semen out of the penis.


The primary functions of the penis are urination, erection, and ejaculation. Each involves a complex series of involuntary and voluntary processes.

Congenital Abnormalities

There are several congenital conditions that can cause a penis to be abnormally formed. Congenital disorders are those that are present at birth caused when something interferes with the normal development of an unborn baby. Congenital penis abnormalities are usually caused by an imbalance of hormones that influence penis development.

Hypospadias and Epispadias

Hypospadias is a condition where the opening of the urethra is on the underside of the penis rather than at the tip. It is one of the most common congenital abnormalities in males. Epispadias is a similar condition in which the urethra opens on the top side of the penis.

Surgery is generally recommended to correct hypospadias either during infancy or early childhood. However, there are risks of long-term complications, including difficulty urinating and an increased risk of urinary tract infections.


Chordee is the abnormal curve of the penis at the time of birth. It is more common in males with hypospadias but can also occur on its own. In adolescent and adult males, chordee is most noticeable during an erection.

Chordee vs. Peyronie's Disease

Chordee should not be confused with Peyronie's disease. Peyronie's is a condition that occurs spontaneously in adult males that causes an abnormal curve of the penis.


Micropenis is an abnormally small penis. It is defined as a stretched penis that is at least 2.5 times smaller than what would be expected at that stage of a male's development. In adults, this would be stretched penis of less than 2-3/4 inches.

Micropenis affects 1.5 out of 10,000 male children in the United States. It is thought the be caused by abnormally low production of male hormones, called androgens, during pregnancy.


The congenital absence of a penis, called aphalia, is an extremely rare condition affecting one of every 30 million births. It usually occurs with other congenital abnormalities affecting the heart or digestive tract. The cause of aphalia is unknown. So far, less than 100 cases have been reported.


Congenital penis abnormalities are rare but can cause the abnormal placement of the urethra (hypospadias, epispadias), the abnormal curve of the shaft (chordee), an abnormally small penis (micropenis), or no penis at all (aphalia).

Dysfunction and Diseases in Later Life

There are a number of medical conditions that can affect the function or appearance of the penis in later life. These may affect the glans, foreskin, urethra, or erectile tissues.

Erectile Dysfunction

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

Peyronie's Disease

Peyronie's disease (PD) is the abnormal curve of the penis that occurs in later life. Studies suggest that around 0.5% of adult males will experience PD at some time in their life. The risk increases as you get older.

Peyronie's disease is mainly the result of a prior injury to the penis during sex. With that said, PD is poorly understood and may occur spontaneously for no known reason. If the symptoms of PD are severe, they can cause erectile dysfunction.

Penile Fracture

A penile fracture occurs when the thick membrane surrounding the corpus cavernosa, known as the tunica albuginea, ruptures during vigorous sex. The tunica albuginea is supplied with a rich network of blood vessels that can cause bleeding and severe pain when ruptured. The scar tissue that results from a penile fracture may lead to Peyronie's disease.

Phimosis and Paraphimosis

Phimosis is a condition where the foreskin is too tight to be pulled back over the head of the penis. Phimosis is normal in babies and toddlers, but, in older children, it may be the result of a skin condition that has causes scarring. It is not usually a problem unless it causes symptoms.

Paraphimosis occurs in uncircumcised males when the foreskin gets stuck in the retracted position. It is a medical emergency that can lead to tissue death if not treated immediately.


Priapism is an erection that lasts more than four hours. It is not always the result of sexual arousal and can be quite painful. Priapism occurs when blood becomes trapped in the penis and is unable to drain. If the condition is not treated immediately, it can lead to scarring and permanent erectile dysfunction.

Priapism can occur in males of any age and is more common in those with certain blood diseases like sickle cell disease and leukemia. Certain medications can also increase the risk of priapism.

Penile Inflammation

The penis is vulnerable to infection. This includes sexually transmitted diseases like genital herpes or human papillomavirus (HPV) that affect the skin and gonorrhea or chlamydia that can affect the urethra. These and other infections can lead penis inflammation.

Inflammatory conditions affecting the penis include:

  • Balanitis: Inflammation of the head of the penis
  • Posthitis: Inflammation of the foreskin
  • Balanoposthitis: Inflammation of the head and foreskin
  • Urethritis: Inflammation or infection of the urethra
  • Urethral stricture: The abnormal narrowing of the urethra

Penile Cancer

Penile cancer is very rare. However, it can be one of the more aggressive forms of cancer. Around 95% are caused by a type of skin cancer called squamous cell carcinoma. Penile cancer is diagnosed in fewer than one per 100,000 males each year and accounts for fewer than 1% of all cancers in the United States.


The tests used to diagnose disorders of the penis vary by the symptoms and suspected cause. You may be referred to a doctor known as a urologist who specializes in disorders of the urinary tract and male reproductive organs.

Erection Problems

The diagnosis of erectile dysfunction starts with a review of your symptoms and sexual and medical history. This includes any medications you take and any emotional problems you may be experiencing.

The doctor may also order imaging studies like an ultrasound or magnetic resonance imaging (MRI) that can evaluate soft tissues and blood flow. Penile imaging is often done while the penis is erect using the injection of a drug like Caverject (alprostadil) that causes vasodilation (the widening of blood vessels). Other tests may be used to see if you get erections at night, such as nocturnal tumescence testing.

The same tests and procedures are used in men with conditions like Peyronie's disease that can cause erectile dysfunction.


If there is pain, inflammation, and discharge from the penis, the doctor will usually screen for sexually transmitted diseases or other infections. This may include blood tests, urine tests, or a swab from inside the urethra.

If there are abnormal growths on the skin of the penis, a biopsy may be performed to obtain a sample of tissue for examination in the lab.

Urination Problems

Problems with urination are usually investigated with a urinalysis that checks for abnormalities in the composition of your urine. This includes looking for pus and inflammatory chemicals that can occur with a urinary tract infection.

In older men especially, a prostate-specific antigen (PSA) test may be ordered to check for an enlarged prostate. A digital rectal exam may also be performed by inserting a finger into the rectum to check the size and consistency of the prostate gland.

A test called a voiding cystourethrogram may also be ordered if you have difficulty urinating. The test, which takes images while you are urinating, can help identify if there is a blockage or strictures.


The penis is a complex organ used for urination, sex, and reproduction. It contains a rich network of blood vessels that can cause the engorgement of the penis, leading to an erection. Ejaculation is achieved by an involuntary contraction of muscles and vessels that proper semen from the body. The same tube that is used for ejaculation, called the urethra, is also used for urination.

Different conditions can affect the appearance or function of the penis. Some are congenital and cause the malformation of the penis during fetal development. Others occur later in life and may be caused by injury, infections, or diseases like cancer.

An examination by a urologist may be needed to diagnose and treat disorders of the penis.

Frequently Asked Questions

  • How does the penis become erect?

    Sexual arousal or other stimulation sends messages from the brain to the nerves around the penis, causing the muscles to relax and letting blood flow into the penile arteries. This stretches the penis out, creating an erection.

  • When is penis pain a serious problem?

    Many relatively minor conditions can cause penile pain. However, you should contact your healthcare provider immediately if you have pain that lasts more than four hours, have pain with other unexplained symptoms, or develop priapism (an erection that does not go away).

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17 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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