Penis Anatomy, Function, and Conditions

The penis is a complex external organ used to urinate and for sex and reproduction in people who are born biologically male. The anatomy of the penis includes the head, shaft, and foreskin. The shaft contains erectile tissue as well as the urethra, which carries urine out of the body.

In this article, the terms "male" and "male anatomy" are used to describe the physical characteristics of both cisgender males (whose sense of personal identity and gender corresponds to their birth sex) and people with penises whose sense of personal identity and gender may not correspond to their birth sex.

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.

Penis Anatomy

The penis is one of the external organs of the male reproductive system (used for sex and to conceive babies) and the urinary system (used to "pee"). It is located at the front of the body at the base of the pelvis. The scrotum, containing the testes (a.k.a. testicles), is situated just beneath the penis.

The penis consists of several major structures:

• Glans: The glans, or head of the penis, is the sensitive structure at the end of the corpus (shaft).
• Urethra: The urethra is a tube inside the penis that runs from the bladder to the head of the penis. It is used for urination. It also crosses through the prostate gland, where an opening (called the ejaculatory duct) receives sperm and fluids that mix together to form 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.

Functions of the Penis

The primary functions of the penis are urinary and sexual. The sexual function of the penis can be described as two stages: erection and ejaculation.

Urination

Urination is the release of urine (pee) from the body. This occurs when urine passes from the bladder through the urethra to the meatus. The urine is pushed out of the body by the contraction of the detrusor muscle in the wall of the bladder.

Between the penis and the bladder is the external sphincter muscle, which can be controlled to hold in or release urine.

Erection

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

Ejaculation

Ejaculation is the discharge of semen from the penis. It 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 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 most of the 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.

Congenital Penis Abnormalities

There are several congenital conditions that can cause a penis to be abnormally formed. Congenital disorders are those that are present at birth and caused by something that interferes with the normal development of the fetus.

Congenital penis abnormalities are usually caused by an imbalance of male or female sex hormones that influence penis development.

Hypospadias and Epispadias

Hypospadias is a condition in which 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

Chordee is an 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.

Micropenis

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 2.75 inches.

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

Aphalia

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, fewer than 100 cases have been reported.

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 with a penis 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 an abnormal curve of the penis that occurs in later life. Studies suggest that around 0.5% to 13% of adult males will experience PD at some time in their lives. The risk increases as a person gets 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 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 in which the foreskin is too tight to be pulled back over the head of the penis. Phimosis is normal in male babies and toddlers, but, in older children, it may be the result of a skin condition that causes scarring. It is not usually a problem unless it causes symptoms.

Paraphimosis occurs in an uncircumcised penis 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

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 at any age and is more common in males 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 infections like genital herpes or human papillomavirus (HPV), which affect the skin, and gonorrhea or chlamydia, which can affect the urethra. These and other infections can lead to 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 (cancer of the penis) is very rare. However, it can be one of the more aggressive forms of cancer. Around 95% of cases 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.

Diagnosis

The tests used to diagnose disorders of the penis depend on 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) scan to 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 those with conditions like Peyronie's disease that can cause erectile dysfunction.

Infections

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

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

Urination Problems

Problems with urination are usually investigated with a test called a urinalysis that checks for abnormalities in your pee. This includes looking for pus and inflammatory chemicals that can occur with a urinary tract infection (UTI).

Especially in people who are older, a prostate-specific antigen (PSA) test may be ordered to check for an enlarged prostate. A digital rectal exam (DRE) 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.

Seeking Help

Whether you are cisgender male, a transgender man, or don't identify as either male or female, your health concerns remain the same if you have a penis. If you have problems with reproduction, urination, or any other penis-related concern, you need to have the condition looked at by a specialist such as a urologist.

To find a culturally sensitive, gender-affirming specialist in your area, speak with your primary healthcare provider or reach out to your nearest LGBTQIA center for advice. You can also check the provider list offered by the Gay & Lesbian Medical Association (GLMA) or the provider locator managed by the World Professional Association for Transgender Health (WPATH).

Summary

The penis is a complex organ used for urination, sexual activity, and reproduction in people born biologically male. 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 propel semen from the body. The same tube that is used for ejaculation, called the urethra, is also used for urination (peeing).

Different conditions can affect the appearance or function of the penis. Some are congenital and cause abnormalities of the penis during the development of the fetus. 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.