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 [tes´tis] (L.)
the male gonad; either of the paired, egg-shaped glands normally found in the scrotum; called also testicle. The testes produce the spermatozoa (the male reproductive cells) and testosterone (the male sex hormone), which is responsible for the secondary sex characters of the male.
A, Testis; B, production of spermatozoa.

If the testes are removed (castration, bilateral orchiectomy) before puberty, the male is sterile and will never develop all the adult male secondary sex characters. If they are removed after puberty, the male becomes sterile and his secondary sex characters will diminish unless he receives injections of male hormones. With aging, there is a gradual decrease in the production of testosterone.

In the fetus in utero, the testes lie close to the kidneys. During approximately the seventh month of fetal life, the testes begin to descend through the abdominal wall at the groin and enter the scrotum. As they descend they are accompanied by blood vessels, nerves, and ducts, all contained within the spermatic cord. The passageway through which the testis and spermatic cord descend is called the inguinal canal. Failure of a testis to descend into the scrotum is called cryptorchidism.

The testis is divided internally into about 250 compartments or lobules, each of which contains one to three small convoluted tubules, within which spermatozoa are produced. When mature, the spermatozoa leave the tubules and enter the epididymis (situated on top of and behind each testis), where maturation is completed. The spermatozoa are stored in the epididymis until such time as they are mixed in the semen and ejaculated during coitus. (See also reproduction and male reproductive organs.)
Cancer of the Testis. Testicular cancer accounts for about 12 per cent of all cancer deaths in young men in North America and is second only to accidents as a cause of death in men between the ages of 20 and 35 years. It is one of the most curable forms of cancer when detected early and treated promptly. Men most at risk for testicular cancer are those who have an undescended or partially descended testicle.

In order to ensure early detection of cancer of the testis, men are urged to conduct a monthly self-examination of the testes. The self-examination involves the use of both hands to examine each of the testes. The index and middle fingers are placed below the testis and the thumbs on top. With a gentle motion each testis is rolled between the thumbs and fingers to discover any lump (usually about the size of a pea), thickening, or change in the consistency of the tissues. It is important that the man become familiar with the feel of the epididymis so that he doesn't confuse this normal structure with an abnormal lump. Should a lump or any other abnormality be found, a doctor should be consulted immediately. The American Cancer Society publishes several pamphlets that explain the procedure for testicular self-examination and give additional information on testicular cancer. Diagnosis of testicular cancer is confirmed by biopsy of the suspect testis. There are three stages of classification for malignancy of the testis: Stage I: the tumor is confined to the affected testis; Stage II: the malignancy has spread to the regional lymph nodes; and Stage III: there is metastasis to other organs, such as the lung and liver.

Treatment of testicular cancer (simple orchiectomy for Stage I malignancy) may or may not render the patient impotent and sterile. If there is no metastasis, only the affected testis need be removed. The remaining testis will retain its normal function and the patient should be able to have normal sexual intercourse and be fertile. However, if more radical surgery and radiation therapy are called for and both testes and the lymph nodes are dissected, and if there has been no damage to nerves during surgery, the patient may be able to have sexual intercourse but no seminal fluid will be emitted. A young man who is looking forward to having children may consider banking his sperm prior to surgery so that he might father children by artificial insemination.
Testicular self-examination. (Redrawn from For Men Only. New York, American Cancer Society.)
abdominal testis an undescended testis located in the abdominal cavity.
canalicular testis an undescended testis located between the internal and external inguinal rings.
cryptorchid testis undescended testis.
ectopic testis one lodged in a location outside of the normal pathway of descent.
gliding testis an undescended testis that can reach the top of the scrotum but then glides back up.
obstructed testis an ectopic testis whose descent was prevented by a fascial sheet at the entrance to the scrotum.
retained testis undescended t.
retractile testis a testis that can descend fully into the scrotum but moves freely up into the inguinal canal.
undescended testis
1. a testis in the normal pathway of descent but failing to descend into the scrotum; see also cryptorchidism. Called also cryptorchid or retained testis.
vanishing testis one that was originally present in the fetus but atrophied in utero because of torsion.


, pl.


(tes'tis, -tēz), [TA]
One of the two oval male gonads (reproductive glands), located in the cavity of the scrotum. The seminiferous tubules of the testis are the site of spermatogenesis and its Leydig cells secrete testosterone as well as estrogens and other androgenic steroid hormones.
See also: appendix testis.


a testis.


, pl. testes (tes'tis, -tēz) [TA]
One of the two male reproductive glands, normally located in the cavity of the scrotum.
See also: appendix of testis
Synonym(s): orchis [TA] , didymus, testicle.


a testis; also used as a word termination designating a fetus with duplication of parts or one consisting of conjoined symmetrical twins.