The penis, which carries semen and urine out of the body, is an important part of the male reproductive system. Dr. Jerman, can you tell us about the penis?
Sure, Dr. Reynolds. There are three tubes inside the penis: the two corpora cavernosa and the urethra. The three tubes are wrapped together by a tough, fibrous layer of connective tissue called the tunica albuginea.
The corpora cavernosa are two spongy tubes that are soft until they fill with blood. During sexual arousal, nerve messages release chemicals that increase blood flow into the coropora cavernosa. The smooth muscle in the corpora cavernosa relaxes, which lets blood enter and stay in these tubes. The pressure of the blood makes the penis firm, resulting in erection.
The urethra is a hollow tube that carries urine from the bladder through the penis to the outside of the body. It also receives sperm from the vas deferens and fluid from the seminal vesicles and prostate, which mix to form semen. Semen travels through the urethra and out of the penis during ejaculation.