How the Body Defends and Repairs Itself
In order to live to reproductive age, each of us must fight off an almost continuous onslaught by disease and virulent organisms. Over the centuries, we have developed an exceedingly sophisticated, complex and effective system of defenses. Its effectiveness is attested to by the fact that we are still here, although for almost all of man’s existence there was no formal medical help available.
As various life forms evolved, so did the defensive mechanisms of the organism. Even the relatively simple life forms such as amoebae and other unicellular “animals” have complicated defenses. But immunologic mechanisms, the most sophisticated protection we have, did not appear until the development of animals with backbones, the first traces appearing in primitive marine vertebrates 400 million years ago. About 250 million years ago, a system comparable to man’s appeared in higher sharks, and since then there have been additional refinements to produce the complicated, many faceted system of reptiles, birds and finally mammals.
The methods that the human body has developed to maintain its integrity can be divided into two broad groups: those that are primarily defensive and those that are reparative.
The defensive methods can be further subdivided into those that attempt to prevent invasion by external agents such as chemicals, particles and organisms (bacteria and viruses), and those that operate once the first-line defenses have failed and our body has been “invaded.”
