You feel sick and run down, so you schedule an appointment with your doctor. You tell him all of your symptoms, but he doesn’t tell you what’s wrong. Instead, he has the nurse take blood from you. What is he looking for? What does blood have to do with your sore throat or aching head?
The Body's Hit Men
Your doctor probably wants to know how many white blood cells you have. A healthy adult has between 4,000 and 10,000 white blood cells in each micro liter of blood, which means that you have thousands of these cells in a droplet the size of a single crystal of salt. White blood cells defend your body against intruders such as bacteria, viruses, fungi, and allergens. When your body is under attack, it makes more white blood cells. The cells travel through your blood and eliminate the attackers. So, if you have any sort of infection, your white blood cell count will usually be greater than the high end of the normal range.
Doctors also use blood tests to determine what types of white blood cells your body is making. There are five main types of white blood cells, and different types target different intruders. By looking at your white blood cell counts, your doctor can tell whether your sore throat is the result of a virus, bacteria, or something else. From there, he can decide which further tests you’ll need or what medications will help you. He can even find out what diseases you’ve had in the past, or if you’ve ever received vaccinations for certain diseases.
Take a look at how a virus invades the body: http://www.youtube.com/watch?v=Rpj0emEGShQ
Watch the videos below to see a white blood cell in action, learn more about the body’s immune system, and discover how vaccines work.