Prostate, PROS tayt, gland is an organ of the male reproductive system. It produces a thick whitish fluid that helps transport sperm. All male mammals have some form of prostate gland. In men, this gland sits just below the urinary bladder and directly in front of the rectum. The urethra, the tube through which urine leaves the body, passes through the prostate. The gland weighs about 2/3 ounce (20 grams) and is about the size of a walnut. It consists of muscular and glandular tissue with a tough, fibrous covering.