What are testicles?

The testicles are a part of the male reproductive system. They are also called the testes; one testicle is called a testis. In adult males, these 2 organs are each normally somewhat smaller than a golf ball. They are contained within a sac of skin called the scrotum, which hangs beneath the base of the penis.

The testicles make male hormones, mostly testosterone. They also make sperm. Sperm cells go from the testicle to a coiled tube inside the scrotum (the epididymis) where they are stored. Sperm travel from the epididymis through the vas deferens to the seminal vesicles, where they are mixed with fluid from the prostate gland. During ejaculation, sperm cells, seminal vesicle fluid, and prostatic fluid enter the urethra and go out the tip of the penis. The urethra is the tube in the center of the penis through which urine or semen leaves the body.