white blood cells are very specialized. They attack only certain pathogens. You will read
about these white blood cells in Lesson 4.
Otherwhitebloodcellsattackanypathogenstheyfind. Thesewhitebloodcellstraveltosites
of inflammation. They are calledphagocytes, which means “eating cells.” In addition to
pathogens, phagocytes“eat”deadcellsandotherdebris. Theyengulfthepathogensordebris
and destroy them. This process is calledphagocytosis. How phagocytosis occurs is shown
inFigure21.19. You can watch a video of an actual phagocyte gobbling up and destroying
a pathogen athttp://sciencevideos.wordpress.com/category/phagocytosis/.
Figure 21.19: These drawings show phagocytosis. In this process, a phagocyte engulfs and
breaks down a pathogen. ( 2 )
White blood cells also produce chemicals that cause a fever. Afeveris a higher-than-normal
body temperature. Normal human body temperature is 98.6° F (37° C). Most bacteria and
viruses that infect people multiply fastest at this temperature. When the temperature is
higher, the pathogens cannot multiply as fast. A fever also triggers the immune system to
make more white blood cells. In these ways, a fever helps the body fight infection.
Lesson Summary
- Yourbody’sfirstlineofdefenseincludestheskinandotherbarriersthatkeeppathogens
out of your body. - If pathogens enter your body, inflammation occurs, and phagocytes come to the body’s
defense.