The prostate is a small gland about the size of a ping pong ball. It sits just below the bladder and surrounds the upper part of the urethra – the tube that carries urine from the bladder and semen from the testicles to the outside of the body through the penis.
What does the prostate do?
The prostate produces most of the fluid that mixes with sperm to make semen. During sex the muscles of the prostate help force prostate fluid and sperm into the urethra via ejaculation.
The male sex hormone, testosterone, made in the testicles, controls how the prostate works.
The prostate also produces a protein called prostate-specific antigen (PSA). This helps to make semen watery.