The penis is one of the external structures of the male reproductive system. The penis has three parts: the root, which attaches to the wall of the abdomen; the body, or shaft; and the glens penis, which is the cone-shaped end (head). The opening of the urethra, the tube that transports semen and urine, is at the tip of the glens penis.
The body of the penis is cylindrical in shape and consists of three internal chambers. These chambers are made up of special, sponge-like erectile tissue. This tissue contains thousands of large caverns that fill with blood when the man is sexually aroused. As the penis fills with blood, it becomes rigid and erect, which allows for penetration during sexual intercourse. The skin of the penis is loose and elastic to accommodate changes in penis size during an erection.
Semen, which contains sperm (the male reproductive cells), is expelled through the end of the penis when the man reaches sexual climax (orgasm). Disorders of the penis can affect a man's sexual functioning and fertility.
