Basic Science Flashcards
Exogenous
Infectious agent is not normally found on or in the body
Endogenous
Infectious agent that can be routinely found on the body but does not normally cause disease
How do exogenous agent cause disease
When it enters the host from the environment
How do endogenous agents cause disease
Overcomes innate host immunity to cause disease
Vector
Insects and other carriers that transmit disease
Zoonotic hosts (reservoirs)
Animals that harbor infectious agents
Nosocomial infections
Hospital acquired infections. Happens when the normal flora is colonized with other bacteria
What is a physical barrier
Something that impedes the entry of bacteria from the external environment into sterile areas of the body
Examples of physical barriers
Skin, mucous membranes, secretions, perspiration, nose hairs, hair on arms/legs, gastric acids (pH)
Commensals
Organisms that live symbiotically on or within the human host but rarely causes disease
Where are the normal flora of the body located
- Skin - staph
- Oropharynx - strep
- LI - enterococci, enteric bacilli
- Vagina - lactobacilli
- Colon - bacteroides
What do commensal bacteria secrete
TLR ligands, which bind to TLR on surface of normal intestinal tissue. This stimulates basal signaling which protects the cells of the intestine from injury (i.e., when abx are introduced)
Carrier
Anything that carries and transfers bacteria to a susceptible individual
Opportunistic infections
Infections that result from normal flora (commensals) or from environment that usually do not cause disease (not considered human pathogens). immunocompromised hosts
Colonization
When normal flora is overgrown by endogenous or exogenous organisms. (i.e. broad spectrum abx will kill lactobacilli in the vagina, which will then allow for the colonization of candida).
3 host defense mechanism to inhibit colonization of bacteria
- Mechanical clearance
- Phagocytic killing
- Depriving organism of nutrients
What site is usually easier for colonization
Sterile areas of the body because there are fewer microbes. However the immune system will be vigorous
Congenital infections
Acquired in utero
The complement system is part of which immunity
Innate immunity
What are the major cytokines involved in an inflammatory reaction when a microbe enters the body
Interleukin-1, 6, TNF, and interferon-y. Secreted by macrophages
What are the acute-phase reactants
Rheumatoid factor
C-reactive protein
Ferritin
Proteinase inhibitors
What is the complement system composed of
Plasma proteins and cell membrane receptors (the C proteins, produced by the liver)
What are the two pathways of the complement system
Classic and alternative. Mostly mediated by C3 and terminal components C5-C9
What activates the complement system
Antigen-antibody complexes. Directly activate C1
What activates the alternative pathway
Mechanisms independent of antibodies, usually interactions with bacterial surface carbohydrates (“nonspecific).. Microbe binds directly to C3
What do both pathways ultimately proceed towards
Creation of a MAC, which results in target cell lysis. C3 and C5-C9 must be activated, which then makes C3 convertase enzyme, then MAC.