Penis is seen to consist of three major buildings as we see on below. The top 2 of them (corpus cavernosum) are the structures who provide erection. The third in the bottom called the corpus spongiosum and has the structure which provides the evacuation of urine from the bladder through the urethra (urine tube). However, the sperm produced by the testes and all the produced semen at once discharged in secondary sex organs. There is an elastic membrane that protects penis except all these structures (tunica albuginea). Inside of Corpus spongiosums consists of a spongy tissue and thanks to this structure, it is provided the formation and maintenance of erection.