Body defenses can be divided into physical barriers, innate immunity, and adaptive immunity. Physical barriers include skin, mucous secretions, acids in sweat and the stomach, washing by tears, and gut flora. These are the first level of defense.
Immunity is the ability to resist infection and disease. It is divided into innate and adaptive immunity. Innate immunity is non-specific. We are born with specialized cells and circulating proteins, such as complement, that provide defense against many types of foreign invaders. Adaptive immunity acts on specific, foreign antigens. It employs a different set of immune cells and anitbodies.
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