Our bodies are continually being attacked by bacteria and viruses. We must have defense mechanisms or otherwise we would be sick all the time. 

Defense mechanisms fall into two categories:

• Keep the germs out of the body (that is what skin does)
• Fight the germs once they get inside the body (that is what the immune system does)

Vaccines & Disease
When your grandparents were children, a disease called polio was causing hundreds of thousands of children to be crippled for life, as their muscle cells were destroyed by the virus.  Some children had to live inside an "iron lung" that breathed for them because their chest muscles were dead and they were unable to breathe on their own. During the 1950's, this frightening disease was stopped, however, because of the polio vaccine.  (View more about polio.)

Another major disease, smallpox, raged for hundreds of years in all parts of the world. The disease was so common and deadly that a worldwide campaign to eliminate it began when a vaccine was developed.  The vaccine left a scar on the skin, but it was worth it to prevent smallpox.  Because so many people around the world were vaccinated, the disease has apparently disappeared. No reports of smallpox have appeared since 1979, when it was declared to be eradicated.  (Access more information about the role of vaccination in eradicating smallpox.)

Of course, we don't always have vaccines that work against some diseases. Throughout this unit, we will learn how the body fights diseases both with and without the help of vaccines. We will introduce the structures and functions involved in bodily defenses that keep you safe and healthy.

Introduction | Why It Matters | How We Find Out | What We Know | Story Time
Common Hazards | Activities | Self-Study Game | Teachers Pages | Standards (TEKS)