Penis

The penis is the external sex organ of the male through which both urine and semen pass. It consists of three cylinder-shaped bodies of spongy tissue filled with tiny blood vessels, which run the length of the organ. Two of these bodies lie side by side in the upper portion of the penis. The third is a tube which lies centrally beneath the others and expands at the end to form the tip of the penis, which is called the "glans." The penis transfers sperm to the woman's body during sexual intercourse and is a duct for the disposal of fluid waste. The penis becomes erect during sexual excitement, because extra blood is pumped into spongy tissues, resulting in enlargement and hardening which allows penetration into the female organ. The "head" of the penis is called the "glans" and is normally covered with a protective, retractable skin or "hood." This skin is often cut off at birth, or "circumcised," and it is believed that its removal lessens risk of cancer and bacterial infections. At the center of the penis is a tube which carries urine from the bladder and semen from the prostate gland, called the "urethra." During sexual intercourse, reflexes prevent urine from entering this duct and alkaline solutions are produced and secreted to flush out any traces of urine from the urethra before semen is secreted.