Anatomy of the penis

There are two types of erectile tissue in the penis, namely the corpora cavernosa and the corpus spongiosum. During sexual arousal, blood fills these spaces (it's analogous to a Reebok pump shoe) and causes erection.

The cone-shaped glans penis at the distal end of the penis is an extension of the corpus spongiosum. The glans penis is covered by a loose fold of skin called the prepuce or foreskin. Circumcision is the surgical removal of the foreskin, usually done for religious reasons.