The prostate is a part of the male reproductive system. It adds nutrients and fluid to sperm. Normally the size of a walnut, the prostate can be divided into right and left "lobes."It is located in front of the rectum, just below the bladder. It surrounds the urethra, the tube that carries urine and semen through the penis.
The growth of cells in the prostate, both healthy and cancerous, is stimulated by testosterone. Male hormones, including testosterone, are produced almost entirely by the testicles, with only a small percentage produced by adrenal glands (small glands found just above the kidneys).