What Are Testicles?

The testicles produce sperm and testosterone, a male sex hormone.

The testicles are male sex glands that are part of the reproductive system.

Males have two egg-shaped testicles, or testes, which may be slightly different in size.

The testicles are responsible for the production of sperm as well as testosterone, an important male sex hormone.

Anatomy of the Testicles

The testicles are located in the scrotum, a sac of skin that hangs below the penis and between the legs.

Each testicle is held in place by a spermatic cord, which is made of tough connective tissue and muscle surrounding the vas deferens (a large sperm-carrying duct), blood vessels, lymph vessels, and nerves.

The testicles have a fibrous covering called the tunica, which consists of two layers: the inner tunica albuginea and the outer tunica vaginalis.

The tunica albuginea divides the testicles into individual sections called lobes, or lobules.

Altogether, the lobules contain about 800 seminiferous tubules — tightly coiled U-shaped tubes that connect to the rete testis, a network of uncoiled, interconnected channels.

The rete testis, in turn, connects through ducts to another tightly coiled tube — the epididymis. The epididymis is composed of a head, body, and tail that connect to the vas deferens.

Function of the Testicles

There are two main types of cells that allow the testicles to produce sperm and hormones: germ cells and supportive stromal cells.

Germ cells line the seminiferous tubules and produce sperm. The tubules also contain a type of stromal cell called Sertoli cells, which help the germ cells produce and transport sperm.

Sperm travel through the long maze of the seminiferous tubules and rete testis, ending up in the epididymis, where they fully mature over the course of a few weeks.

Once they are mature, sperm move to the vas deferens, where they combine with fluids from the nearby prostate gland and seminal vesicles, forming semen.

During ejaculation, the sperm-carrying semen is pushed out of the body through the urethra in the penis.

Aside from Sertoli cells, there are various other types of stromal cells that serve different purposes.

Leydig cells — specialized stromal cells — are located within the soft connective tissue in between the seminiferous tubules, beneath the tunica albuginea, and in the septum tissue that divides the scrotum into two areas.

These important cells are the body's main source of testosterone.

As a male sex hormone, testosterone helps the germ cells make sperm and is vital to the development and function of the male reproductive organs.

In addition, testosterone gives men libido (sex drive).

Testosterone is also responsible for producing secondary sex characteristics in men, such as a deep voice, body and facial hair, and enlarged muscles and body size.

Diseases and Conditions of the Testicles

A wide range of diseases or health issues may affect the testicles, including:

• Undescended testicle, in which one or both of the testicles fail to move into the scrotum before birth
• Testicular trauma, which may cause scrotal swelling and pain
• Testicular torsion, in which the spermatic cord gets twisted, cutting off the testicles' blood supply (also painful)
• Epididymitis, an inflammation of the epididymis, and orchitis, an inflammation of one or both of the testicles, which are often caused by sexually transmitted diseases, such as chlamydia and gonorrhea
• Primary hypogonadism, in which the testicles don't produce enough testosterone

Though relatively rare, testicular cancer may also develop in the germ cells. Stromal cells may also develop tumors, which are typically benign.