Testicle with Exposed Internal Structure: Medical visualization of a single human testicle with a wedge removed to see the interior; also visible is the epididymis, pampiniform venous plexus, and the testicular artery. The testes are the male gonads, and perform two functions: to manufacture motile sperm and produce male sex hormones, namely testosterone. The center of the testis contains the seminiferous tubules (arranged in lobes that radiate from a central plexus) where sperm production, or spermatogenesis, occurs. Resting directly on top of the testis is a single convoluted tube called the epididymis, where sperm are stored while they mature. Upon ejaculation, sperm enter the vas deferens and leave the penis through the urethra. Leydig cells, which reside in the testis, produce male sex hormones called androgens. The androgen testosterone develops secondary sexual characteristics and maintains sperm development sites. The pampiniform venous plexus and the testicular artery service the testicular area.

The testicle (from Latin testiculus, diminutive of testis, meaning "witness" of virility, plural testes) is the male gonad in animals. Like the ovaries to which they are homologous, testes are components of both the reproductive system and the endocrine system. The primary functions of the testes are to produce sperm (spermatogenesis) and to produce androgens, primarily testosterone.

Both functions of the testicle are influenced by gonadotropic hormones produced by the anterior pituitary. Luteinizing hormone (LH) results in testosterone release. The presence of both testosterone and follicle-stimulating hormone (FSH) is needed to support spermatogenesis. It has also been shown in animal studies that if testes are exposed to either too high or too low levels of estrogens (such as estradiol; E2) spermatogenesis can be disrupted to such an extent that the animals become infertile.

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