The prostate is a small gland that is part of the male reproductive system. A normal, healthy prostate is about the size and shape of a walnut. Its position in the body is just below the bladder and in front of the rectum. The urethra- the tube that carries urine from the bladder and semen out through the penis- runs through the center of the prostate. The function of the prostate is to produce some of the seminal fluid that nourishes and carries sperm from the testicles and out of the penis during ejaculation. Because of its position an enlarged prostate can squeeze the urethra causing urinary problems.