What is a menstrual period?
When puberty begins, your brain signals your body to produce hormones. Some of these hormones prepare your body each month for a possible pregnancy. This is called the menstrual cycle. Hormones cause the lining of the uterus to become thicker with extra blood and tissue. One of your ovaries then releases an egg. This is called ovulation. The egg moves down one of the two fallopian tubes toward the uterus.
If the egg is not fertilized with a man’s sperm, pregnancy does not occur. The lining of the uterus breaks down and flows out of the body through your vagina. The discharge of blood and tissue from the lining of your uterus is your menstrual period (also called “your period”).