White blood cells
These fight infections. There are three sorts of white blood cell – granulocytes, monocytes and lymphocytes. They all play a different role in fighting infection.
This is the tube that carries air to your lungs. It starts just below your voicebox in your neck and carries on inside your ribcage until it gets to the bottom of your breastbone. It then divides into two bronchi.
You have four wisdom teeth right at the back of your mouth, but they don’t usually come through until your late teens to early twenties. When they come through, they may be in the wrong place, so you may need them removed.