Penis: anatomy, function, disease and diagnosis


The penis is a complex external organ in men that is used to urinate, have sex, and reproduce. It consists of several parts, including the shaft, the head, and the foreskin. A channel called the urethra runs through the center of the rod and allows urine and ejaculation to pass through . The trunk 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 located in the center of the front of the body at the base of the pelvis. The scrotum , which contains the testicles, is located under the penis.

The penis is made up of several basic structures:

  • Glans : The glans of the penis is a sensitive bulbous structure at the end of the body (shaft).
  • Urethra : The urethra is a tube that runs from the bladder to the glans of the penis and is used for urination. It also travels through the prostate gland , where semen and ejaculatory fluid, which make up semen, enter through an opening called the vas deferens.
  • Meatus : The meatus is the opening at the tip of the glans penis through which urine or semen leaves the body.
  • Foreskin : The foreskin , or foreskin, is a loose fold of skin that covers the glans of the penis. Removing the foreskin is called circumcision .
  • Corpora cavernosa: The corpora cavernosa are two columns of spongy tissue that run along the inner shaft of the penis. When filling with blood, the tissues harden and cause an erection.
  • Corpus spongiosum : The corpus spongiosum is the third column of tissue that prevents the urethra from closing during erection.

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

The average length of the penis in a flaccid (soft) state is 3.5 inches. The average length of an erect penis is 6 inches with an average girth of 5 inches.


The penis consists of a body (shaft), a glans (glans), and a foreskin (foreskin). The urethra is the tube that carries urine or semen out of the body. The spongy columns of tissue within the shaft can fill with blood and cause an erection.


The main functions of the penis are urination and sexual life. The sexual function of the penis can be divided 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 anus. Urine is excreted by contraction of the detrusor muscle in the bladder wall.

At the base of the penis is the external sphincter muscle , which men can flex freely to "pump" excess urine from the body and allow the bladder to empty.


An erection is the stiffness of the penis caused by sexual arousal and / or physical stimulation. It is also normal for an erection to occur during sleep and upon waking. An erection occurs when blood flow to the corpora cavernosa and spongius increases.

During an erection, the arteries that serve erectile tissue dilate (dilate), causing the penis to fill with blood. The swelling simultaneously compresses the veins that normally carry blood out of the penis. This "traps" the blood and helps maintain an erection.


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

Ejaculation involves a series of simultaneous involuntary muscle contractions:

  • First, a tube called the vas deferens narrows, pushing sperm from the testicles into the vas deferens.
  • At the same time, the prostate gland and seminal vesicles contract, adding fluids that make up most of the semen.
  • At the same time, the rapid contraction of the muscles at the base of the penis, called the periurethral muscles, pushes the semen out of the penis.


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

Congenital anomalies

There are several birth defects that can make the penis misshapen. Congenital disorders are those that are present at birth when something interferes with the normal development of the fetus. Congenital anomalies of the penis are usually caused by an imbalance in the hormones that affect the development of the penis.

Hypospadias and epispadias

Hypospadias is a condition in which the opening of the urethra is at the bottom of the penis and not at the tip. This is one of the most common birth defects in men. Epispadias are a similar condition in which the urethra opens at the top of the penis.

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


Curvature of the penis during childbirth. It is more common in men with hypospadias, but it can occur on its own. In adolescents and adult men, the curvature of the penis is more noticeable during erection.

Chordi against Peyronie's disease

Chordi should not be confused with Peyronie's disease . Peyronie's disease is a condition that occurs spontaneously in adult men and causes an abnormal curvature of the penis.


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

The micropenis affects 1.5 out of every 10,000 male children in the United States. It is believed to be caused by abnormally low levels of the production of male hormones called androgens during pregnancy.


Congenital absence of the penis, called a bottlenose dolphin, is an extremely rare condition that affects one in 30 million births. This usually occurs with other birth defects that affect the heart or digestive tract. The cause of apalia is unknown. So far fewer than 100 cases have been reported.


Congenital anomalies of the penis are rare, but can cause an abnormal urethral position (hypospadias, epispadias), abnormal curvature of the shaft (curvature of the penis), an abnormally small penis (micropenis), or complete absence of the penis (aphalia).

Dysfunction and illness in later life.

There are a number of conditions that can affect the function or appearance of the penis later in life. It can affect the glans penis, foreskin, urethra, or erectile tissue.

erectile dysfunction

Erectile dysfunction occurs when a person cannot get or maintain an erection enough to have sex. Erectile dysfunction can be caused by medical conditions, including medications or heart disease. It can also be the result of stress, anxiety, or relationship problems.

peyronie's disease

Peyronie's disease (PD) is an abnormal curve of the penis that occurs in adulthood. Research shows that approximately 0.5% of adult men will experience Parkinson's disease at some point in their lives. The risk increases with age.

Peyronie's disease occurs primarily as a result of previous trauma to the penis during sexual intercourse. That said, PD is poorly understood and can occur spontaneously for no known reason. If the symptoms of PD are severe, they can cause erectile dysfunction.

Penis fracture

A penile fracture occurs when the thick membrane that surrounds the corpora cavernosa, known as the white membrane , breaks during vigorous sex. The tunica albuginea has a rich network of blood vessels that, if ruptured, can cause bleeding and severe pain. Scar tissue from a fractured penis can lead to Peyronie's disease.

Phimosis and paraphimosis

Phimosis is a condition in which the foreskin is too tight to retract through the glans of the penis. Phimosis is normal in infants and young children, but in older children it can be the result of a skin condition that causes scarring. This is usually not a problem unless it causes symptoms.

Paraphimosis occurs in uncircumcised men when the foreskin becomes stuck in a retracted position. This is a medical emergency that can lead to tissue death if not taken right away.


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

Priapism can occur in men of any age and is more common in people with certain blood conditions, such as sickle cell anemia and leukemia . Certain medications can also increase your risk of priapism.

Swelling of the penis

The penis is vulnerable to infection. This includes sexually transmitted diseases such as genital herpes or human papillomavirus (HPV) , which affect the skin, and gonorrhea or chlamydia , which can affect the urethra. These and other infections can cause inflammation of the penis.

Inflammatory conditions of the penis include:

  • Balanitis : inflammation of the glans penis.
  • Posthitis : inflammation of the foreskin.
  • Balanoposthitis : inflammation of the head and foreskin.
  • Urethritis : inflammation or infection of the urethra.
  • Urethral stricture : Abnormal narrowing of the urethra

Penile cancer

Cancer of the penis is very rare. However, it can be one of the most aggressive forms of cancer. About 95% of these are caused by a type of skin cancer called squamous cell carcinoma . Penile cancer is diagnosed in less than one person in 100,000 men per year and accounts for less than 1% of all cancers in the United States.


The tests used to diagnose penile disorders vary depending on the symptoms and the underlying cause. You may be referred to a doctor known as a urologist who specializes in diseases of the urinary tract and male reproductive organs.

Erection problems

Diagnosing erectile dysfunction begins with an analysis of your symptoms, as well as your medical history and sex life. This includes any medications you are taking and any emotional problems you may have.

Your doctor may also order imaging tests, such as ultrasound or magnetic resonance imaging (MRI) , which can evaluate soft tissues and blood flow. Pictures of the penis are often taken while the penis is erect, with an injection of a drug such as Caverject (alprostadil) , which causes vasodilation (dilation of the blood vessels). Other tests can be used to see if you have an erection at night, such as a nighttime swelling test .

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


If there is pain, swelling, and discharge from the penis, the doctor will usually look for sexually transmitted diseases or other infections. This may include blood tests, urinalysis , or a urethral swab.

If there are abnormal growths on the skin of the penis, a biopsy may be done to obtain a tissue sample for laboratory analysis.

Urinary problems

Urinary problems are usually tested with a urinalysis , which looks for abnormalities in the composition of the urine. This includes looking for pus and inflammatory chemicals that can occur with a urinary tract infection.

Older men especially may be prescribed a prostate specific antigen (PSA) test to check for an enlarged prostate . A digital rectal exam can also be done by inserting a finger into the rectum to check the size and consistency of the prostate gland.

If you have trouble urinating, you may also have a test called a urinary cystourethrogram . A test that takes pictures while you urinate can help determine if there is a blockage or stricture.


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

Several conditions can affect the appearance or function of the penis. Some of them are congenital and cause malformations of the penis during fetal development. Others occur later in life and can be caused by trauma, infection, or diseases such as cancer.

An examination by a urologist may be required to diagnose and treat diseases of the penis.

Frequently asked questions

  • Sexual arousal or other stimulation sends signals from the brain to the nerves around the penis, causing the muscles to relax and allowing blood to flow into the arteries of the penis. This stretches the penis and causes an erection.

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

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