Definition of Testicles and Function

The paired male organs, also called the male gonads, that produce sperm and androgens, notably testosterone.

Each egg-shaped testicle is about two inches long and an inch in diameter. A man’s testicles may be slightly different from each other in size. The testicles reside side by side in the scrotum, a saclike structure suspended outside the body from the lower pelvis.

The testicles are outside the body because spermatogenesis (the generation, or production, of sperm) requires a temperature two to three degrees below normal body temperature. A hollow ligament, the spermatic cord, extends from the abdomen to the testicle through the inguinal canal, carrying the ARTERY, VEIN, lymph structures, and nerves that supply the testicle.

The outer layer of the testicle is the tunica albuginea, a sheath of fibrous tissue that contains and protects the structures within the testicle. Tightly coiled tubules, the seminiferous tubules and the epididymis, make up the main mass of the testicle. The cells that fill the space between the tubules are the Leydig cells, also called the interstitial cells, which produce testosterone.

The seminiferous tubules contain germ cells, from which new sperm cells (spermatozoa) arise, and Sertoli cells, which nourish and support the developing sperm cells. The Sertoli cells draw testosterone into the seminiferous tubules, which sperm cells require to come to maturation, and prevent antibodies in the blood from entering the seminiferous tubules.

As the sperm cells develop, they travel from the seminiferous tubules to the epididymis, another coiled tubule. The epididymis incubates spermatozoa to maturity during the 12 days or so it takes for them to journey through the convolutions of the epididymis, during which they acquire tails and motility (the ability to move). The vas deferens then carries sperm from the epididymis to the ejaculatory duct, which is within the lower pelvis.

Genital traumaHydrocele
Klinefelter’s syndromeOrchitis
SpermatoceleTesticular cancer
Testicular torsionVaricocele

For further discussion of the testicles within the context of the structures and functions of reproduction and sexuality, please see the overview section “The Reproductive System.”


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