The prostate gland is a male reproductive organ whose main function is to secrete prostate fluid, one of the components of semen.The muscles of the prostate gland also help propel this seminal fluid into the urethra during ejaculation.The prostate is a muscular gland that weighs about three-fourths of an ounce (20 grams) about the size of a small apricot.It surrounds the urethra just beneath the bladder.he prostate is a muscular gland that weighs about three-fourths of an ounce (20 grams) about the size of a small apricot. It surrounds the urethra just beneath the bladder.