Dear loka_2010,

Guys don't have periods because they do not have the reproductive organs (ovaries and a uterus) that allow a woman to menstruate.

Girls have two ovaries. Each one holds hundreds of thousands of very tiny eggs. Until they ripen and are released from the ovary, the eggs are so tiny that you can only see them with a microscope. By the time an egg is released it is the biggest cell in the human body — about as big as the head of a common pin. Girls are born with all the eggs they will ever have. An ovary releases an egg about once a month. This is called ovulation.

The egg moves through a tube toward the uterus. Most of the time, the egg breaks apart before it gets to the uterus. But that doesn't always happen. If a sperm from a boy's penis meets the egg on its way to the uterus, they can join together. The joining of an egg and a sperm is called fertilization. Pregnancy begins if a fertilized egg attaches itself to the lining of the uterus.

Before the ovary lets an egg go, the uterus begins building up a lining. It is made of tissue and blood like almost everything else inside us. The lining is like a nest for the egg if pregnancy happens. If it doesn't happen, the egg breaks apart, and the lining of tissue and blood isn't needed. It flows out of the uterus, through the cervix, through the vagina, and out of the woman's body. This is called menstrual flow. A woman is having her period when this happens.

Hope this information helps!

Take care,

teenwire.com^® Editors

This column is for informational purposes only and is not intended to constitute medical advice, diagnosis, or treatment. If you have a medical problem, please call toll-free 1-800-230-PLAN for an appointment with the Planned Parenthood health center nearest you.