The most important function of the prostate gland is the production of seminal fluid, according to PubMed Health. The prostate also changes testosterone to a biologically active form and assists in closing off the section of the urethra that runs to the bladder to keep semen from entering during ejaculation.
The portion of semen formed in the prostate is necessary for the sperm cells to function properly, and thus is important to a man's fertility, explains PubMed Health. The prostate contains enzymes, including prostate-specific antigen, that thin the semen. It also contains spermine, a hormone-like substance that primarily enables sperm cells to move. This fluid is combined with fluids from other glands and sperm cells from the testes in the urethra prior to ejaculation.
The prostate works together with the bladder sphincter muscle during ejaculation to prevent semen from entering the bladder, and muscles in the prostate also close off the seminal ducts to prevent urine from entering them during urination, states PubMed Health. The prostate assists in the conversion of testosterone to dihydrotestosterone, a much more potent hormone, notes the Society for Endocrinology. This conversion is necessary for many of the effects of testosterone to manifest in the body.