The male has paired testes, each protected by a its own sac separated within the scrotum, which hangs outside the body, by the scrotal septum. Sperm grow optimally at a temperature 2C below that of body temperature. The cremaster muscles associated with each testis and the dartos muscle of the scrotum contract to bring the testes closer to the warm body when it is cold or relax when it is hot, to maintain optimal temperature.
The tunica vaginalis is the serous covering of each testis. Inside the vaginalis, is the tunica albuginea, a fibrous covering. Each testis consists of a large number of lobules (300-400) that contain seminiferous tubules. Sperm are produced and develop in the seminiferous tubules. Sertoli cells envelop and nourish developing sperm cells. Leydig (interstitial) cells produce testosterone in the presence of luteinizing hormone (LH). Immature sperm are released into the tubule lumen and pass into the coiled tubes of the epididymis where they mature and are stored until needed.
A spermatic cord connects each testis to the body. It contains the vas deferens that carries sperm into the ducts of the male reproductive system, blood vessels, lymphatics, and nerves. The pampiniform plexus of veins in the spermatic cord act as a heat exchanger. Their blockage may cause sterility.
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