The prostate is a walnut-sized gland found only in men. It plays an important role in reproduction by helping to produce the fluid in semen.
The prostate is positioned just below the bladder and surrounds the urethra, which passes urine from the bladder to outside the body. The prostate is tiny at birth but after puberty it enlarges, due to the rising levels of testosterone.
The prostate gland manufactures an important liquefying component of semen. Sperm are produced in the testicles and then stored just behind the prostate in the seminal vesicles. Here, and at the time of ejaculation, the sperm are in a jelly-like medium. At orgasm and ejaculation, the prostate and seminal vesicles contract, mixing their respective contents. The fluid in the prostate contains large amounts of a substance known as prostate specific antigen (PSA), which liquefies the previously gelatinous sperm mixture, allowing the sperm to move freely in search of an ovum to fertilise.
The prostate is the only organ that continues to grow throughout life. This can cause problems once a man reaches middle age. The earlier men recognise a problem with their prostate and seek help, the better the outcome of treatment is likely to be.