Testes Anatomy and Function

The testes are the organs that make sperm and testosterone

The testes, or testicles, are two egg-shaped sex organs that play an important role in the male reproductive system. They are where sperm cells are produced and are also responsible for the production of the sex hormone testosterone.

The testes, commonly referred to as "balls," are housed in a pouch of skin beneath the penis called the scrotum. Their location outside the abdomen ensures that the testes remain cooler than body temperature and create the optimal environment for sperm cells to develop.

This article discusses the anatomy of testes, including their function and medical conditions that can harm them or lead to infertility.

Males testes, illustration

For the purpose of this article, the term male refers to people with penises irrespective of their gender identity or whether they identify with any gender at all.

Anatomy of the Testes

Most males are born with two testes. These are soft, egg-shaped organs located inside the scrotum.

Within the scrotum, the testes are suspended from the abdomen by the spermatic cord. This is a collection of blood vessels, nerves, and ducts that support the health and function of the testes.

The testes are made up of several lobes that contain a network of narrow tubes called seminiferous tubules. These are where sperm are produced in a process known as spermatogenesis. As the sperm cells develop and mature, they move through these tubules until they reach a wider conduit called the rete testes.

They are then passed to a tightly coiled tube on the outside of each testicle called the epididymis. This is where sperm cells are stored and complete maturation.

In adult males, the testes are around 2 to 3 centimeters wide and roughly 3 to 5 centimeters long. The testes increase in size through adulthood and then decrease in size later in life due to the natural decline in testosterone.

Function of the Testes

The testes have two primary functions.

The first is to produce testosterone. Testosterone is a hormone that is responsible for secondary male characteristics such as facial hair, body hair, and increased muscle mass. It also contributes to libido (sex drive), sexual function, and male fertility.

Testosterone and Male Fertility

Testosterone is secreted by cells called Leydig cells that are situated between seminiferous tubules in the testicles.  In the absence of testosterone, sperm cells cannot mature as they should, resulting in infertility.

The second function of the testes is to produce sperm. Unlike females, who can only produce a limited number of eggs over a lifetime, males are able to produce millions and millions of sperm each day. It then takes several months for the sperm cells to mature enough to be functional. The maturation starts in the testes but mostly takes place inside the epididymis.

Congenital Disorders Affecting the Testes

There are a number of congenital conditions that can affect either the location or appearance of a testicle. Congenital conditions are those that occur during fetal development.


Cryptorchidism is a condition where one or both testicles have not moved into the scrotum prior to birth. Also known as an undescended testicle, it is one of the most common congenital conditions affecting male babies.

Cryptorchidism in infants is not considered a medical emergency, and many times the testicle will descend on its own.

If the testicle has not descended within the first few months, a surgical procedure known as orchiopexy may be used to repair the abnormality. This is because cryptorchidism can expose the testicle to higher body temperatures within the abdomen, increasing the risk of infertility and testicular cancer.

Retractile testis is a similar condition in which a testicle moves back and forth from the scrotum to the abdomen. As long as the testes spend most of their time in the scrotum, it is not considered as problematic as undescended testes and may not require treatment.


In addition to undescended testicles, there are times when a male baby may be born with no testicles, one testicle, or more than two testicles.

When a person is born with more than two testicles, the condition is referred to as polyorchidism. People with polyorchidism most commonly have three testicles but can have as many as five. It is a very rare condition with fewer than 200 reported cases.

Transverse Testicular Ectopia

Transverse testicular ectopia, or crossed testicular ectopia, is an equally rare condition. It occurs when both testicles descend to the same side of the scrotum.

Transverse testicular ectopia usually occurs alongside other congenital conditions such as hypospadias (in which the opening of the urethra is not at the tip of the penis).

Medical Conditions Affecting the Testes

Beyond congenital disorders affecting the testes, there are also medical conditions that can affect the testes later in life.


Orchitis refers to inflammation of the testes. In sexually active young males, it is most commonly due to the sexually transmitted infections chlamydia and gonorrhea. Pain and swelling are the central features.

In older males and children, orchitis may be caused by a bacterial or viral infection.


Varicocele is another common condition affecting the testes. It involves an abnormal enlargement of veins within the scrotum (similar to varicose veins) that can starve the testicles of the blood needed to produce healthy sperm.

Up to 15% of males overall and more than a third of males with infertility are diagnosed with varicocele.

Testicular Torsion

Testicular torsion occurs when the testicle rotates inside the scrotum, cutting off the blood supply. Symptoms include pain and swelling of the testicle, typically sudden and severe. Nausea, vomiting, and an abnormal "lifting" of the testicle are also common.

When to Seek Emergency Care

Testicular torsion is a medical emergency. Unless the flow of blood is restored within six hours, the risk of testicular damage and infertility is high. Severe cases can even result in the loss of the testicle.

Testicular Cancer

Testicular cancer affects thousands of males each year in the United States. Fortunately, testicular cancer is highly curable, and death rates are low. Unlike other cancers, it is more likely to affect younger males.

Symptoms of testicular cancer include a painless lump on a testicle, a dull ache in the groin or abdomen, a feeling of heaviness in the scrotum, and back pain.


The diagnosis of testicle problems usually involves a physical examination and imaging studies to look for abnormalities within or surrounding the testicle.

Physical Exam

A physical examination can help detect lumps, swelling, or other abnormalities on or around the testes. This may involve palpation (the light touching of tissues). The healthcare provider may also manipulate your leg, pelvis, or torso to check for pain or the abnormal movement of a testicle.

Imaging Studies

Ultrasound is the most commonly used tool to examine the testes. This non-invasive test uses sound waves to look inside the scrotum for any abnormalities. It can also check if the blood flow is normal or for signs of testicular torsion, testicular cancer, and varicocele.

Magnetic resonance imaging (MRI) uses powerful magnetic and radio waves to create highly detailed images of soft tissues. An MRI is the test of choice for diagnosing cryptorchidism. It can also help differentiate benign (non-cancerous) lumps from malignant (cancerous) ones.


The testes (testicles) are two egg-shaped organs housed within the scrotum that play a central role in male fertility and function. They are tasked with producing sperm as well as the sex hormone testosterone.

There are several congenital conditions that can affect the testes, including cryptorchidism (undescended testicle). The testicles are also vulnerable to other medical conditions such as orchitis, varicoceles, testicular torsion, and testicular cancer.

A Word From Verywell

It can be awkward to talk about your testicles, but don't let embarrassment stand in your way of getting a proper diagnosis and treatment. Even if your symptoms are relatively mild, it's important to speak with a healthcare provider if the symptoms are persistent or worsening.

If your primary care provider is unable to pinpoint the cause, ask for a referral to a urologist who specializes in diseases and disorders of the male reproductive tract.

Frequently Asked Questions

  • What is a testis?

    Testis is the medical term for a single testicle. The plural of testis is testes. The testes are the male reproductive organs that make sperm and the hormone testosterone. The testes (commonly known as balls, nuts, rocks, stones, or bollocks) are housed in the scrotum. Testes can also be called testicles.

  • What are testes made from?

    The testes are covered in a membrane called the tunica vaginalis which allows them to move around within the scrotum. Each testicle is encased in a fibrous capsule called the tunica albuginea. Each testicle contains a network of tubes, known as seminiferous tubules, where sperm are produced

  • What are the first signs of testicular cancer?

    The first sign of testicular cancer is the appearance of a hardened, painless lump. With that said, most lumps in the testicles are not cancerous. Only an examination by a healthcare provider can determine whether the growth is benign (non-cancerous) or malignant (cancerous).

9 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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By Elizabeth Boskey, PhD
Elizabeth Boskey, PhD, MPH, CHES, is a social worker, adjunct lecturer, and expert writer in the field of sexually transmitted diseases.