Our bodies are constantly being challenged by viruses, microbes, protozoa,
and fungi. The immune system protects us from such foreign invaders and
keeps us healthy.
Occasionally, the challenge makes us sick. Then the immune system finds
the pathogens,eliminates them, and returns the body to a healthy condition.
Part of our defenses are general against any type of invader. But another
part of the immune system is very specific for the exact microbe that
makes us sick. Not only does the immune system return us to health, but
it remembers the first encounter and protects us from getting sick again
from the same pathogen.
The cells of the immune system are produced in the bone marrow and circulate
in the blood and lymph. Wherever microbes enter the body, the cells of the
immune system mobilize to combat the invasion.
We will take a look at the way the body defends itself against foreign
invaders and examine some of the diseases in our environment.