Thursday, April 30, 2009

How Does The Body Defend Against Infection

Suppose a pathogenic agent (an organism that is capable of causing an infection) does invade the body. The threat is that it will cause disease, either because it is present in great members (as in pneumonia) or because it can release toxins (as in botulism, TSS, tetanus, or diphtheria). What can the body to do fight off the pathogen?

The Outer Defenses
The skin and mucous membranes are the body’s first line of defense. An invading microbe must find its way through the skin or the mucosae, the mucus-coated membranes that make an “inner skin” for the body by lining the respiratory, digestive, and urogenital tracts. Here are also secretions, such as tears, perspiration, skin oils, and saliva, that contain chemicals that can kill bacteria. In addition the respiratory passages are lined with fine, short, moving hairs called cilia. Beating in synchronized fashion, the cilia move a carpet of sticky mucus. The mucus works like fly paper to trap inhaled microbes and foreign matter and carry them to back of the throat, where they are removed by sneezing, coughing, or nose-blowing, or are swallowed and disposed of by digestive fluids.

Besides the cilia, other body hairs (the eyelashes, for example) may fend off invading microorganisms. Our reflexes (coughing, blinking, vomiting) are also part of our body’s firs line of defense. High acid levels in the stomach and vagina also help destroy invaders.

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