Which of the following is not among the first line of...

Which of the following is not among the first line of defenses against infection?
a. skin
b. lysozyme in saliva
c. resident populations of bacteria
d. acidic gastric fluid
e. complement activation
f. flushing action of diarrhea

Key Concepts

Innate Immunity

The body’s innate immunity comprises the first line of defense, which includes non-specific mechanisms that prevent pathogens from entering the body. These mechanisms act immediately or within hours of encountering an antigen, providing a rapid response to infection.

Physical Barriers

Physical barriers such as the skin and mucous membranes serve as the first physical defense against invading pathogens. They function by creating a physical blockade that prevents microbes from accessing underlying tissues.

Chemical Barriers

Chemical barriers involve substances that naturally exist on bodily surfaces, like lysozyme in saliva and acidic gastric fluids. These chemicals help destroy or inhibit the growth of microbes and are an essential part of the body's immediate defense strategy.

Resident Microflora

Resident microflora, or the normal bacterial populations present on the skin and within the gastrointestinal tract, act as a competitive barrier to pathogenic organisms. They help maintain a balanced microenvironment and prevent colonization by harmful bacteria.

Complement System

The complement system consists of a series of proteins in the blood that, upon activation, enhance the ability of antibodies and phagocytic cells to clear pathogens. Although it is part of the innate immune response, its activation is typically considered a secondary line of defense rather than a primary barrier mechanism.

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