Nearly everything in the environment -water, food, and even the air -teems with microbes. The human body has three cooperative lines of defense that protect us from the constant barrage of these and other potentially harmful substances (Figure 5.1). The first line of defense is a set of physical barriers and chemical agents that prevent foreign invaders from getting deep inside the body. If that line fails, a variety of internal protections stand ready as a second line of defense. These first two lines of defense are nonspecific -that is, they do not distinguish one infectious microbe from another, but rather respond similarly to every infectious agent. Later in this chapter, we’ll discuss the third line of defense: the immune system, which responds in a customized way to each particular microorganism.
FOR DOWNLOAD, click the link below:-
https://drive.google.com/file/d/0B7yZT6IHPCq4SHVadHpSU2Izc0k/view?usp=sharing
No comments:
Post a Comment