 With such a large exposure (more than three times larger than the exposed surface of the skin), these immune components function to prevent pathogens from entering the blood and lymph circulatory systems.Fundamental components of this protection are provided by the intestinal mucosal barrier which is composed of physical, biochemical, and immune elements elaborated by the intestinal mucosa.Microorganisms also are kept at bay by an extensive immune system comprising the gut-associated lymphoid tissue (GALT)

There are additional factors contributing to protection from pathogen invasion.