Bodily Defenses Image Map

Oh no, zits!
Many teenagers have a frustrating time dealing with the little bumps on their face called "pimples". Instead of focusing on how to treat them, let's discuss why the small pustules (zits) typically appear as white bumps. 

Why are they white?  It is because of the white blood cells (see the photo of a white blood cell on the right). If you smeared the pustule on a glass slide, stained the slide, and looked at it under a microscope you would actually be able to see the white blood cells! The white blood cells are attracted to bacteria under your skin. Why?

Remember the description of a splinter from the introduction to the unit? The splinter and the bacteria on it crossed the first line of defense, the skin. The second line of defense is the white blood cells. White blood cells are attracted to wounds or areas where bacteria has injured the skin. The white blood cells become concentrated in an area, as they block bacteria from entering surrounding tissues. Your first and second lines of defense, the skin and immune system, work together to keep your body healthy and free from infection.

Why do white cells gather at the site of injury? There must be some kind of signal to attract them to leave the blood and to gather at the injury site. Likewise, it seems natural to suspect that the white blood cells have something in them that neutralizes or destroys bacteria.
How can we learn about the ways in which white blood cells protect us from infection? 

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