A normal prostate gland is approximately the size and shape of a walnut or golf ball, according to Mayo Clinic. It's located between the bladder and the penis, directly in front of the rectum. The prostate surrounds the urethra, which carries urine from the bladder to the penis.
The prostate is responsible for nourishing and protecting the sperm, which it does by producing a fluid that is expelled with the sperm as semen during ejaculation, says WebMD. As most men age, their prostates increase in size, often leading to urination and bladder difficulties, as the prostate can apply pressure to the urethra, states MedlinePlus.