Even if they don’t ask about it, boys who are 13+ years old are curious about how puberty is different for girls. They are particularly interested in learning about girls and their periods. They hear their friends who are girls talking about it, but most boys are too embarrassed to ask about it.
One important piece of information that answers the question about where the blood comes from during a period, can be explained using these illustrations from my book I’m a Boy, How Are Girls Different?
Illustrations from I’m a Boy, How Are Girls Different?
The drawing on the left shows the basic anatomy of the uterus and the lining inside is called the endometrium. During each menstrual cycle, the endometrium slowly fills with tiny blood vessels. If there is a pregnancy, the tiny baby grows inside the endometrium and gets nutrients from fluid that leaks out of the tiny blood vessels.
The drawing on the right shows what happens to the endometrium at the end of the menstrual cycle if there is not a pregnancy. The tiny blood vessels break open and this is where the blood comes from for the girl’s period. Blood leaves the uterus and drips into the vagina and out of the body. There is about 2-3 tablespoons that drips out over about 4-7 days.