The Human Body

Testis

Testis, also called testicle, is one of a pair of male sex glands that produce sperm cells. Testes are present in most animals. In backboned animals the testes produce male sex hormones, called androgens, as well as sperm.

In man the testis is an oval organ about 5 cm (about 2 in) long. During embryonic development it is located in the abdominal cavity, but about a month before birth it normally descends into a pouch of skin called the scrotum. Each testis contains about 800 narrow twisting tubes, called seminiferous tubules, that are lined with cells that, upon maturation, divide to form the sperm. The seminiferous tubules merge and form a larger tube, the epididymis. Sperm travels from the testis through the epididymis to the vas deferens, which carries the sperm to the urethra. Sperm exits from the urethra during ejaculation (the release of semen during orgasm). In man the sex hormone produced by the testis is testosterone, which controls the growth of the male reproductive system and stimulates the development of the male secondary sexual characteristics, such as the growth of the beard, the deepening of the voice, and the male contours of the body. It also influences male sexual behavior (see Human Sexuality).

See also TESTICULAR CANCER and DISORDERS