Innate Immunity

Immune defenses that do not change their response to repeated exposure to an antigen comprise innate immunity. The timing and magnitude of the response is therefore the same regardless of the number of exposures to the antigen. The three classes of infectious organisms are bacteria, viruses, and parasites (protozoa, fungi, helminthes, and nematodes). Despite its limitations the innate system is equipped to respond to each type of pathogen.

The first lines of defense against microbial challenges are the mechanical barriers. The skin is a barrier impermeable to microbes that prevents them from entering the body. Secretions of apocrine and eccrine glands containing lactic acid and fatty acids are also on the surface of the skin and inhibit the growth of microorganisms. Similarly, the mucosal surfaces of the body serve as a barrier to infection and secrete substances (saliva, gastric acid, tears, etc.) that impede microbial growth. Additionally, actions like sneezing, coughing, increased peristalsis, and ciliary movement actively expel irritants and infectious agents.

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