The testicles

The testicles (testes) are part of a man’s reproductive system. A man has 2 testicles. Each testicle is egg-shaped and about 5 cm long. The testicles are covered by a sac of skin called the scrotum. The scrotum hangs below the penis, between the legs. The testicles make sperm. They also make testosterone, which is a male sex hormone.


Each testicle is covered by tough, fibrous layers of tissue called the tunica. The outer layer is called the tunica vaginalis and the inner layer is called the tunica albuginea.

The testicle is divided into parts called lobules. Each lobule contains tiny U-shaped tubes called seminiferous tubules. There are about 800 seminiferous tubules tightly coiled within each testicle.

The seminiferous tubules open into a series of uncoiled, interconnected channels called the rete testis. Ducts, or tubes, connect the rete testis to a tightly coiled tube called the epididymis. The epididymis joins to a long, large duct called the vas deferens.

Each testicle is held in the scrotum by a spermatic cord. Each spermatic cord is made of tough connective tissue and muscle. It contains the vas deferens, blood vessels, lymph vessels and nerves.

Lymph fluid travels through vessels in the spermatic cord and drains from the testicles into several groups of lymph nodes at the back of the abdomen. These lymph nodes are called the retroperitoneal lymph nodes.

What the testicles do

The testicles make sperm and male hormones. The 2 main types of cells in the testicles that perform these functions are germ cells and stromal cells.

Germ cells

The process of making sperm starts in germ cells, which line the seminiferous tubules. As they mature into sperm cells, germ cells move from the lining, through the maze of seminiferous tubules and to the epididymis. The epididymis stores sperm cells so they can completely mature.

Mature sperm cells travel through the vas deferens. Along the way, fluids made by the seminal vesicles and the prostate gland mix with the sperm cells to create semen. The semen is pushed out of the body through the urethra during ejaculation. Sperm in the semen can fertilize a female egg to start a pregnancy.

Stromal cells

Stromal cells help other cells in the testicle. Different types of stromal cells do different things.

Sertoli (nurse) cells are a type of stromal cell found in the seminiferous tubules. They support the germ cells by helping make and transport sperm.

The soft connective tissue in the space between the seminiferous tubules contains specialized stromal cells called Leydig cells. They make male sex hormones, mostly testosterone. Testosterone helps germ cells make sperm. Testosterone also helps the reproductive organs develop and function. It gives men:

  • sex drive (libido)
  • fully developed genitals
  • a deep voice
  • body and facial hair
  • bigger muscles and body size

Expert review and references

  • American Cancer Society . What Is Testicular Cancer? . 2018 :
  • Cancer Research UK . About Testicular Cancer . Cancer Research UK ; 2017 :
  • Martini FH, Timmons MJ, Tallitsch RB. Human Anatomy. 7th ed. San Francisco: Pearson Benjamin Cummings; 2012.
  • National Cancer Institute . Testicular Cancer Treatment (PDQ®) – Patient Version . Bethesda, MD : National Cancer Institute ; 2018 :
  • Reuter, VE . Anatomy and Pathology of Testis Cancer. Scardino PT, Lineham WM, Zelefsky MJ & Vogelzang NJ (eds.). Comprehensive Textbook of Genitourinary Oncology. 4th ed. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins; 2011: 31:532-543.
  • Young B, O'Dowd G, Woodford P (eds.). Wheaters's Functional Histology. 6th ed. Churchill Livingston; 2014.

Medical disclaimer

The information that the Canadian Cancer Society provides does not replace your relationship with your doctor. The information is for your general use, so be sure to talk to a qualified healthcare professional before making medical decisions or if you have questions about your health.

We do our best to make sure that the information we provide is accurate and reliable but cannot guarantee that it is error-free or complete.

The Canadian Cancer Society is not responsible for the quality of the information or services provided by other organizations and mentioned on, nor do we endorse any service, product, treatment or therapy.

1-888-939-3333 | | © 2024 Canadian Cancer Society