Your penis has a variety of parts and serves many important purposes.  Penis is a complex organ. It is made of muscle, tissue, veins, arteries, and nerves. It begins inside your body near your prostate gland.

Basically, the penis is a kind of "hydraulic" machine. For an erection, the most important part is the corpora cavernosa. These are two cavities that run the length of your penis and actually fill with blood to create an erection.

How you get an erection...

When you become sexually stimulated an erection starts.  The nervous system sends chemical messages to your pelvic area. The smooth muscles inside your penis relax. The arteries widen. The corpora cavernosa, acting like a sponge, fill with blood. Actually the corpora absorbs up to eight times more blood than when your penis in flaccid state.

When the penis lengthens and swells, the filled corpora cavernosa press against the veins. The pressure greatly reduces the blood flow from your penis. This keeps your erection firm enough for sexual intercourse with you partner.

How penis enlargement work ?! Your penis has 3 chambers which fill with blood during an erection. These chambers are a collection of blood vessels which become swollen with blood during sexual arousal. The corpa cavernosa consists of two spongy bodies of erectile tissue on either side of the penis. An erection is caused by blood filling the erectile tissues. But what if the erectile tissues were made larger? What if you could somehow expand the size of the erectile tissues?

Then of course the erectile tissues would hold more blood and you would have a significantly larger penis. Blow up a balloon with more air and you have a larger balloon. Fill the erectile tissues with more blood and you have a larger penis.