What Is the Prostate?

Medically Reviewed

The prostate is a gland located at the base of a man’s bladder, behind the pubic bone and in front of the rectum. This gland, roughly the size and shape of a small crab apple, weighs only about an ounce in young men. It surrounds the urethra, the tube that carries urine away from the bladder and transports semen during ejaculation. A good way to envision the prostate is as an apple with the core removed, with the urethra passing through the middle.

The prostate’s primary function is to produce prostatic fluid, a component of semen. Also, during ejaculation, smooth muscles in the prostate contract to help propel semen through the urethra.

Technically the prostate is not part of the urinary system. But because of its location and relationship to the urethra, the prostate can (and often does) affect urinary function.

Benign Prostatic Enlargement

At age 20, the prostate is about the size of a walnut. When a man reaches his mid-40s, the area of the prostate that encircles the urethra begins to grow. This overgrowth of prostate tissue is called benign prostatic enlargement (BPE), also known as benign prostatic hyperplasia (BPH). By age 70, the average prostate has doubled in size. In some men, the expanding prostate may constrict the urethra, causing symptoms such as difficulty starting urination or a weak urine stream.

BPE occurs to some degree in 80 percent of men, but only about one-third develop lower urinary tract problems significant enough to require treatment. Although BPE is not life threatening, it is responsible for 6.4 million doctor visits and more than 400,000 hospitalizations each year.

Prostate cancer

Cancer of the prostate is a much more serious health problem than BPE. After skin cancer, it is the second most common cancer in American men and is second only to lung cancer as a cause of cancer deaths. Annually, eight times as many men are diagnosed with prostate cancer as die of it.

The good news is that today, reliable diagnostic tests and numerous treatment options are available, and death rates from prostate cancer are now on the decline. Nearly 100 percent of men are still alive five years after a prostate cancer diagnosis, 99 percent are alive 10 years after diagnosis, and about 94 percent are alive 15 years after diagnosis.

Prostate cancer rarely causes symptoms until far advanced. By contrast, BPE commonly causes urinary symptoms. Having BPE neither increases nor decreases a man’s risk of developing prostate cancer. However, it is possible for a man to have both conditions at the same time.

Structure of the prostate

The prostate is made up of three kinds of cells: glandular (epithelial) cells, smooth muscle cells and stromal cells. The glandular cells produce part of the prostatic fluid or semen. The smooth muscles contract to push prostatic fluid into the urethra during ejaculation. Smooth muscles are involuntary, which means they are not under the conscious control of the individual. Stromal cells make up the support structure of the prostate.

The prostate can be divided into three main regions or zones. Immediately surrounding the urethra is the transition zone. In this zone is the tissue that begins to grow in BPE.

The second region is the central zone, which contains a portion of the prostate’s glandular tissue. The largest and outermost region is the peripheral zone next to the rectum, which is the area containing the largest proportion of glandular tissue and the site where most prostate cancers develop.