BRUISES

You bump your arm. You bump it hard. You do not get cut. Your skin does not break. Still, you get a bruise. Your skin turns blue-black. Why does this happen?
Blood flows in your body through tubes. Tubes that carry blood are called blood vessels. You have so many blood vessels in your body. You have enough blood vessels to go around the world! Some tubes are big. Some tubes are tiny.
Living things are made of cells. Cells are like building blocks. They are the smallest building block of living things. Your body has lots of cells. You have bone cells. You have skin cells. You have blood cells, too. You have lots of blood cells. Red blood cells make your blood look red.
When you get bumped, you may hurt some tiny blood vessels. Some may break. You bleed under your skin. When blood cells leak from the tubes, they die. When the cells die, they turn blueblack. We see the blue-black color. We call the blue-black color a bruise.
After many days, the bruise changes color. It changes from blue-black to purple. It changes from purple to yellow. Finally, the bruise is gone.