9781422280300

Allergies and Other Immune System Disorders

Skin is the body’s first line of defense against pathogens; it’s also the site of many immune responses, such as this baby’s eczema.

cells that destroy would-be intruders. They are helped by enzymes that make your skin a drier, more acidic, and less comfortable place for harmful bacteria and fungi. Other parts of your body interact with things from the outside. Your respiratory system breathes in foreign substances through your nose and mouth, drawing air into your lungs. Whenever you eat or drink, you introduce more foreign substances into your digestive system. The entire length of the digestive system is lined with another barrier that protects you from potential invaders: mucus . This slimy, sticky stuff is produced by the mucosa, or mucus membranes. Mucosa also protects your respiratory system, your reproductive system, and

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