The prostate is a complex gland, the approximate size of a walnut, and surrounds the urethra, which is the tube or canal that carries urine, from the bladder, and through and out of the penis.
The primary function of a prostate is the production and delivery of sperm. Sperm is carried in a fluid medium called semen. When a male experiences ejaculation, it is the squeezing action by the prostate for the purpose of expelling the semen through the urethra.