The prostate is a small gland specific to men. About the size of a walnut, the prostate lays between the bladder and the penis and serves to nourish and protect semen. The urethra, the small tube through which urine flows from the bladder, runs through the center of the prostate.
Semen is formed in the testes, the glands located inside the testicles. The semen then travels through the vas deferens, the long, slightly winding tube connecting the testes to the seminal vesicles. The seminal vesicles, which contribute fluid to the semen, lays behind the bladder and also connects to the prostate, joining with the urethra. As the man ejaculates, the semen travels from the seminal vesicles into the urethra, at which point the prostate releases the enriching fluid into the semen. The now enriched semen travels through the urethra through the penis, where it exits the body in the act of ejaculation.
The prostate itself is composed of several lobes. Two lateral lobes make up the largest lobes and meet at the midline of the prostate. A smaller anterior lobe is made of a fibromuscular tissue that contracts to expel semen during ejaculation. The median lobe, found just behind the urethra, is the location of the ejaculatory glands.
The prostate produces fluid to help sperm achieve its primary goal of fertilizing a female egg. The fluid produced by the prostate makes of a large percentage of the semen volume. The secretions of the prostate are milky white and consist of a mixture of simple sugars (such as glucose), enzymes, and alkaline chemicals. The sugars serve as nutrition for the sperm on their journey to the female ova. The enzymes break down the proteins in the semen, freeing the sperm on expulsion from the male body. The alkaline chemicals help to neutralize the acid environment of vaginal secretions, helping the sperm survive. Nourished, free of the viscous semen, and protected from the natural defenses of the female body, the sperm is now able to travel to the ova.