The prostate gland is found only in males and is an essential part of the male reproductive system. It's about the size and shape of a walnut or a small plum in young men. In older men it normally grows to about the size of a lemon. It fits snugly into its position, sitting about 2 inches above the perineum, the muscular area between the scrotum and anus. The prostate's tissue is both glandular and nonglandular. It is made up of thousands of tiny fluid-producing glands interspersed with blood vessels, within a fibromuscular framework.

The urethra, the tube that carries both urine and semen, runs through the prostate gland, and is joined at about the center of the gland by the two seminal ducts. The seminal vesicles sit near the top, rear part of the prostate. The vas deferens, a long tube, connects the urethra with the testes.

The anatomy of the prostate gland can be described in two different ways, by lobe or by zone. Classification by lobe is more common in anatomy, and classification by zone is more common in pathology.

Lobes of the Prostate

• Anterior lobe. The front portion of the gland, lying in front of the urethra, composed entirely of muscle tissue. (Roughly corresponds to part of the transition zone.)
  
• Median lobe. The cone-shaped portion of the gland that sits between the two ejaculatory ducts and the urethra. (Roughly corresponds to part of the central zone.)
  
• Lateral lobes. The two lateral (right and left) lobes are separated by the urethra and form the main mass of the prostate. (The lateral lobes span all zones.)
  
• Posterior lobe. A term sometimes used to describe the rear part of the lateral lobes, which can be palpated through the rectum during a digital rectal exam (DRE). (Roughly corresponds to the peripheral zone.)

Zones of the Prostate

• Anterior zone. Located in the front of the prostate, this zone is composed mostly of muscle tissue.
  
• Transition zone. The innermost part of the gland; surrounds the urethra where it passes through the prostate. This is the part of the gland, along with the central zone, that begins to enlarge after the age of 40.
  
• The central zone. Surrounds the transition zone.
  
• The peripheral zone. Located in the back of the prostate gland. About 70-75% of prostate cancer occurs here.
  

The Prostate Capsule

The prostate capsule is a fibrous membrane that encapsulates the prostate. Extracapsular extension refers to prostate cancer that has spread outside of the prostate capsule and into the surrounding tissues and organs.