T

testicles The paired male organs, also called the
male gonads, that produce SPERMand 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 out-
side the body because spermatogenesis (the gener-
ation, or production, of sperm) requires a
temperature two to three degrees below normal
body temperature. A hollow ligament, the sper-
matic cord, extends from the abdomen to the tes-
ticle through the inguinal canal, carrying the
ARTERY, VEIN, LY M P Hstructures, and nerves that sup-
ply 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 inter-
stitial cells, which produce testosterone. The semi-
niferous 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 anti-
bodies in the BLOODfrom entering the seminifer-
ous tubules.
As the sperm cells develop, they travel from the
seminiferous tubules to the epididymis, another
coiled tubule. The epididymis incubates spermato-
zoa 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 defer-

ens then carries sperm from the epididymis to the

ejaculatory duct, which is within the lower pelvis.

HEALTH CONDITIONS THAT CAN AFFECT THE TESTICLES

CRYPTORCHIDISM EPIDIDYMITIS

GENITAL TRAUMA HYDROCELE

HYPOGONADISM INFERTILITY

KLINEFELTER’S SYNDROME ORCHITIS

SPERMATOCELE TESTICULAR CANCER

TESTICULAR TORSION VARICOCELE

For further discussion of the testicles within the

context of the structures and functions of reproduc-

tion and sexuality, please see the overview section

“The Reproductive System.” For further discussion

of the testicles within the context of the structures

and functions of the endocrine, system please see

the overview section “The Endocrine System.”

See also CONCEPTION; CONTRACEPTION; ORCHIEC-

TOMY; ORCHIOPEXY; PROSTATE GLAND; SEXUAL HEALTH;

VAS DEFERENS; VASECTOMY.

testicular cancer A malignant (cancerous)

tumor that arises from the tissue of a man’s testi-

cle. Testicular cancer is usually unilateral (occurs

only in one testicle), though sometimes occurs

bilaterally (in both TESTICLES), and is most common

in early adulthood (ages 20 to 34). With detection

before the cancer metastasizes (spreads elsewhere

in the body), the cure rate for testicular cancer is

99 percent. Doctors in the United States diagnose

testicular cancer in about 8,000 men each year.

The two main types of testicular cancer are

seminoma and nonseminoma, though some testic-

ular cancers contain a mix of these types. Oncolo-

gists classify mixed testicular cancer tumors as

nonseminoma because the nonseminoma cells

343