The complex structure of three erectile tissues enables the penis to fulfil its functions of urine transportation and reproduction. The urethral corpus cavernosum lies on the underside of the penis and encloses the urethra. The glans corresponds to its outer end, and the urethra opens at the tip. The foreskin encloses the glans.
The two erectile tissues located on the upper side of the penis are responsible for erections. The complex interplay of hormonal and nerve stimulation leads to increased blood flow in the spongy erectile tissue, and to an erection.