The Anatomy of the Testes

The testes are the organs that make sperm and testosterone

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The testes, or testicles, are male sex glands that play an important role in the reproductive system. They are the site of sperm production and are also responsible for the production of testosterone. Testosterone is a steroid hormone that is important for a number of bodily functions, not just sex drive and sperm development.

The testes take the form of two, egg-shaped organs located in the scrotum. The scrotum hangs outside the body. The location of the testes outside the abdomen has evolved, at least in part, because the testes need to stay cooler than body temperature to fully function.

Males testes, illustration


Most males are born with two testicles, collectively known as the testes. These soft, egg-shaped organs are located inside the scrotum. They are surrounded by a number of accessory structures including the epididymis and the vas deferens.

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 of the testes. A person whose testes remain inside their body is said to have undescended testes.

The testes consist of several lobes, each made up of seminiferous tubules. These tubules are the site in which sperm are produced. As sperm develop and mature they move through the tubules until they are collected in the rete testes and then passed through to the epididymis. The epididymis is where sperm mature before ejaculation.

The testes are enclosed in the tunica albuginea. This fibrous capsule surrounds the testes and also divides it into the lobules that contain the seminiferous tubules. The whole mass is then mostly surrounded by the tunica vaginalis. This covering allows the testes to move smoothly inside the scrotum. In adult males, the testes are 2-3 centimeters (cm) wide by 3-5 cm long. The testes increase in size through adulthood and then decrease in size later in life.

Anatomical Variations

There are a number of potential variations in testicle structure.

Cryptorchidism is a condition where one or both testicles have not moved into the scrotum prior to birth. It is one of the most common congenital abnormalities observed in boys. Cryptorchidism in infants is not considered a medical emergency, and many times the testicle will descend on its own. However, it is important to discuss with your child's doctor how often they should be examined to check on their testicular health.

If the testicle has not descended within the first few months of life, the doctor may recommend surgical correction. This is because the testes function best at the lower body temperature inside the scrotum. Men with undescended testicles are thought to be at higher risk of fertility problems and testicular cancer.

In addition to undescended testicles, men may have no testicles, one testicle, or greater than two testicles. The condition where individuals have more than two testicles is referred to as polyorchidism. People with polyorchidism most commonly have three testicles, but men with as many as five testicles have been identified. Polyorchidism is a very rare condition, diagnosed in fewer than 200 individuals.

Transverse testicular ectopia, or crossed testicular ectopia, is a rare condition. It occurs when both testicles descend to the same side of the scrotum, instead of each descending into their own side of the scrotum. This condition usually occurs alongside other developmental conditions affecting the reproductive tract, such as hypospadias (in which the opening of the urethra is not at the tip of the penis).

The Blood-Testis Barrier

The blood-brain barrier is a basic anatomical concept, with implications for disease and treatment. This system protects the brain and makes it difficult for many toxins, drugs, and other substances to affect it. There is a similar barrier in the testes that is referred to as the blood-testis barrier. This barrier protects the developing sperm, reducing the likelihood that their development will be affected by any health or environmental factors. However, it also means that it can be difficult to treat any concerns affecting the health of the testes medically. It also means that it is likely to be very difficult to develop a medically-based contraceptive for men.


The testes have two primary functions. The first function of the testes is to produce testosterone. Testosterone is a steroid hormone that is responsible for sexual differentiation of the male. It is important for prenatal development. It also regulates the development of primary and secondary sexual characteristics—such as penis size and chest hair. In addition, testosterone contributes to the growth spurt that males experience during puberty, bone and muscle growth, and the formation of blood cells.

The second function of the testes is to produce sperm. Sperm develop inside the network of seminiferous tubules that make up a large portion of the testicles. Unlike females, who have a limited number of germ cells that can turn into eggs across the lifetime, men are able to make millions and millions of sperm every single day. It then takes several months for the sperm to mature enough to be functional upon ejaculation. This maturation starts in the testes but mostly takes place inside the epididymis.

Associated Conditions

As mentioned above, cryptorchidism, or undescended testes, are a relatively common congenital condition. Although the affected testicle(s) may descend on their own, they remain at risk of ascending back into the abdomen. This is true even if orchiopexy surgery is performed, which is used to move the testicle into the scrotum. Men with cryptorchidism are at increased risk of fertility concerns and testicular cancer.

Retractile testes are testes that move back and forth from the scrotum to the abdomen. As long as the testes spend most of their time in the scrotum, this is not necessarily considered as problematic as undescended testes. However, if a man has fertility concerns, and/or the testes are mostly in the abdomen, orchiopexy surgery may be used to permanently move the testicles into the scrotum.

Varicocele is another common condition affecting the testes. It involves an abnormal dilation, or increase in size, of the testicular blood vessels and/or abnormally twisted vessels. Up to 15 percent of men in the overall population and more than a third of men with primary infertility experience varicocele. Varicocele is usually discovered at the time of puberty or later, and they are thought to not develop until puberty. Because of anatomical differences, they are more common on the left side of the body than the right.

Testicular torsion occurs when the testicle rotates inside the scrotum, cutting off the blood supply. The symptoms of testicular torsion include pain and swelling of the scrotum, and these symptoms should be reported to a doctor immediately. Testicular torsion is rare, and it is also usually corrected via orchiopexy.

Unlike many other testicular health conditions, testicular torsion can be a medical emergency. The testes need blood to survive and the flow must be restored within six hours of the first symptoms.

Orchitis refers to inflammation of the testes. It is often a response to infection. In young, sexually active adults, this is most commonly due to the sexually transmitted diseases chlamydia and gonorrhea. In men of other age groups, other bacteria and viruses can be responsible. While orchitis can be painful, the pain usually increases slowly rather than coming on suddenly, as with testicular torsion.

Testicular cancer affects thousands of men each year in the United States. Fortunately, it is highly curable, and death rates are low. However, unlike many cancers, testicular cancers are more likely to occur in younger men. Treatment can potentially have a significant impact on fertility as well as quality of life. Therefore, it is important to discuss options with a doctor who is very familiar with the disease.


Ultrasound is the most commonly used technique to examine the testes. This test uses sound waves to look inside the scrotum for any abnormalities in the testes. It can also be used to determine whether there is normal, healthy blood flow. Ultrasound is used in the diagnoses of a variety of testicular health conditions including testicular torsion, testicular cancer, and varicocele. It is not an invasive test, and it should not be painful.

Physical examination of the testes can also be used to detect tumors and other abnormalities of the organ. It is unclear, however, whether it is beneficial for men to perform regular testicular self-exams. Although doing so is recommended by some professional medical organizations, others disagree. There is no consensus that self-exams are useful for men at low-risk of testicular cancer. However, it is something that should be discussed with your physician.

Magnetic resonance imaging (MRI) can also be used to screen the testes. It is the test of choice for diagnosing cryptorchidism in both children and adults, as it allows for imaging of the abdomen. MRI of the scrotum can also be used to characterize types of testicular lesions, including different types of testicular cancer. It may be useful in certain cases of testicular trauma or acute concerns.

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, semen, and the hormone testosterone. The testes—also known as balls, nuts, rocks, stones, or bollocks—are housed in the scrotum.

  • What are testes made from?

    The scrotum covers the testes. On the outside, the scrotum is made up of thin skin and hair, which sit on top of a layer of connective tissue and involuntary muscle known as the tunica dartos. 

    The next layer is the tunica vaginalis, which allows the testes to move around the scrotum.

    Each testis is enclosed in the tunica albuginea, a fibrous capsule that divides it into two lobes. Each lobe contains seminiferous tubules, where sperm is produced, and the epididymis, where sperm mature prior to ejaculation. 

  • What are the signs of testicular cancer?

    The first sign of testicular cancer is the appearance of a hardened, painless lump in the testicle. However, more often than not, a testicle lump is not cancerous. A doctor should evaluate any lump or change in appearance or feel of the testicles. An in-office ultrasound can determine if further testing is needed.

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