YOUR BODY’S PROTECTION AGAINST PATHOGENS: PHYSICAL AND CHEMICAL DEFENSES
Perhaps our single most critical early defense system is the skin. Layered to provide an intricate web of barriers, the skin allows few pathogens to enter. Enzymes, complex proteins manufactured by the body that appear in body secretions such as sweat, provide additional protection, destroying microorganisms on skin surfaces by producing inhospitable pH levels. Normal body pH is 7.0, but enzymatic or biochemical changes may cause the body chemistry to become more acidic (pH of less than 7.0), or more alkaline (pH of more than 7.0). In either case, microorganisms that flourish at a selected pH will be weakened or destroyed as these changes occur. A third protection is our frequent slight elevations in body temperature, which create an inhospitable environment for many pathogens. Only when cracks or breaks occur in the skin can pathogens gain easy access to the body.The linings of the body provide yet another protection against pathogens. Mucous membranes in the respiratory tract and other linings of the body trap and engulf invading organisms. Cilia, hair-like projections in the lungs and respiratory tract, sweep unwanted invaders toward body openings, where they are expelled. Tears, nasal secretions, ear wax, and other secretions found at body entrances contain enzymes designed to destroy or neutralize invading pathogens. Finally, any invading organism that manages to breach these initial lines of defense faces a formidable specialized network of defenses thrown up by the immune system.*18/277/5*
