The prostate is a small gland found only in men. It's about the size of a walnut and gets a little bigger with age. It surrounds the first part of the tube (urethra) that carries urine from the bladder along the penis.
The prostate produces a thick, white fluid that mixes with the sperm produced by the testicles to make semen. It also produces a protein called prostate-specific antigen (PSA) that turns the semen into liquid.
The prostate gland is surrounded by a sheet of muscle and a fibrous capsule. The growth of prostate cells and the way the prostate gland works is dependent on the male sex hormone testosterone, which is produced in the testicles.
The back of the prostate gland is close to the rectum (back passage). Near the prostate are collections of lymph nodes. These are small glands, each about the size of a baked bean.