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pl. testes [L. testis, witness, testicle]
The male gonad; testicle. It is one of two reproductive glands located in the scrotum that produce the male reproductive cells (spermatozoa) and the male hormones testosterone and inhibin.
Each testis is an ovoid body about 4 cm long and 2 to 2.5 cm in width and thickness, enclosed within a dense inelastic fibrous tunica albuginea. The testis is divided into numerous lobules separated by septa, each lobule containing one to three seminiferous tubules within which the spermatozoa are produced by meiosis. The lobules lead to straight ducts that join the rete testis, from which 15 to 20 efferent ducts lead to the epididymis. The epididymis leads to the ductus deferens, through which sperm are conveyed to the urethra. Between the seminiferous tubules are the interstitial cells (cells of Leydig), which secrete testosterone. Within the tubules are sustentacular cells, which secrete inhibin. The testes are suspended from the body by the spermatic cord.
Hyperfunction (hypergonadism) may cause early maturity such as large sexual organs with early functional activity and increased growth of hair. Hypofunction (hypogonadism) is indicated by undeveloped testes, absence of body hair, high-pitched voice, sterility, smooth skin, loss of sexual desire, low metabolism, and eunuchoid or eunuch body type.