What is meant by "nonspecific defenses?"
Basically, it means the general ways that we prevent foreign materials from causing harm to us... as opposed to being able to fight off a specific bacteria that entered our bodies (like how come we don't get chicken pox twice, but we can still get strep throat even after we have gotten it before). Most of the nonspecific defenses are the ways that the human body has barriers to prevent entry of foreign substances.
Types of nonspecific defenses:
When our hand touches a table, the bacteria on the table do not infect us. Why not? Because they cannot enter our bodies due to the presence and design of our skin. Skin and other membranes (like the cornea and the olfactory epithelium) are physical barriers against infection.
The human body secretes chemicals that destroy infectious agents before they can infect us. For example, you learned that our tears contain the enzyme, lysozyme. Lysozyme kills bacteria. That is a chemical barrier to entry of infectious agents through our eyes. We also secrete chemicals in our digestive system that attack potential harmful substances we ingested with our food.
Fevers decrease the spread of infection within our bodies in a roundabout way. You see, as our temperature rises, our liver and spleen sequester iron (they hold onto it rather than putting it back out into the blood). As the general blood iron levels decrease, it makes iron less available to the infectious agents. It turns out that bacteria and fungus need more iron in warmer temperatures. Therefore, by decreasing iron levels with a fever, we decrease the ability of bacteria and fungus to survive in our fevered bodies.
When we do have some sort of tissue damage, like a cut in our skin, that opens the door for infection to occur. However, that door is quickly shut by our inflammation response. You have already learned about inflammation. So you should understand that any entry of foreign material through tissue damage will be met by increased leukocyte interactions at that damaged area. You also know that the clotting process occurs, which surrounds the damaged area with a thick barrier of fibrin filaments; therefore, the infectious agents cannot get past the clot.
Any foreign material that encounters a macrophage or neutrophil will be quickly ingested by those cells through phagocytosis. Phagocytosis allows these cells to destroy the invasive materials. So, anything that slips past our mechanical and chemical barriers, is not affected by or exposed to fever, and doesn't get caught in the inflammatory response, will most likely be destroyed by phagocytosis. Yippee!
The rest of the web pages for this week mainly deal with how we handle those foreign materials that get past all of these nonspecific defenses and find themselves within our bodies. These are the specific defenses, and read on to learn about them!
© 2011 STCC Foundation Press