The testicles, which are also called testes, are a key part of the male reproductive system. The testicles are two oval shaped organs that are located inside the scrotum, which is the loose sac of skin that hangs behind the penis. The testicles are located outside of the body in order to control the temperature of the sperm, which are heat-sensitive.
In the scrotum, the testicles are attached at one end by a structure called the spermatic cord. The spermatic cord contains the blood vessels that supply the testicles and the vas deferens.
The testicles make male hormones, including testosterone, and they produce sperm, the male reproductive cells. Sperm cells are carried from the testicles through a small tube called the vas deferens to the seminal vesicles. Fluid from the seminal vesicles and from the prostate gland is added to the sperm cells during ejaculation to make a substance called semen. Then semen travels out of the body through a tube in the center of the penis called the urethra.