Chapter 3 Flashcards
What are natural immune barriers in the body?
Skin
Resp epithelium
GI and GU adaptations
How does the skin protect with immunity?
First line of defense
Mechanical barrier that provides an unfavorable environment for microbial growth with its acidic pH (5-6) and relative lack of water
How does the respiratory tract protect against infection?
Mucous blanket contains IgA, which captures inhaled particles and steadily rolled toward the mouth by motion of the cilia
Particles are expelled by coughing
Additional protection is offered by the secretory immunoglobulin A (S-IgA)
How do GI adaptations protect against infection?
Acidic pH prevents growth of most bacteria in the stomach, keeping it essentially sterile
Peristalsis and a nl motility pattern keep the bacterial population of the small bowel constant
How do GU adaptations protect against infection?
Urinary tract is normally sterile except at the urethral orifice
Urine also contains IgA, which prevents bacterial adherence to the urothelium
How do normal microflora of the GI tract contribute to host defense?
Occupy potential epithelial binding sites, which limits pathologic microbial penetration. This is known as colonization resistance or tropism
What are the leukocytes responsible for phagocytosis?
Macrophages
Monocytes
Granulocytes
Where are macrophages heavily concentrated?
Lungs
Liver
Spleen
What is chemotaxis?
In this case, where circulating phagocytes migrate to areas of inflammation by following a gradient of chemoattractant molecules
Opsonization
A process by which opsonins (immunoglobulins and complement) bound to the surface of microbes interact with receptors on the phagocyte and promote ingestion
What is the major histocompatibility complex?
The MHC helps macrophages and antigen-presenting cells
What are the MHC subdivided into?
Class I
Class II
What does the antigen-MHC class II complex do?
It binds to T lymphocytes that express the CD4 molecule and are known as helper T cells
What do helper T cells do?
Interact with antigen-presenting macrophages and proliferate into a subpopulation of T-cell clones that recognize the specific antigen(s) and amplify the immune response
Effector cells
Consist of monocytes, macrophages, granulocytes and cytotoxic T cells that express the CD8 molecule
What is the humoral response dependent upon?
Immunoglobulins and complement
What do immunoglobulins do?
Protect the host from infection by
(a) neutralizing viruses and bacterial toxins
(b) inhibiting microbial attachment to host cells
(c) opsonizing pathogens for elimination by phagocytes
(d) activating the complement cascade
What is the first immunoglobulin produced in the initial response to antigen and is a potent activator of the complement?
IgM
What is transported across the placenta from the mother to the fetus and protects the newborn until the 4th mo of life?
IgG
What is the MC immunoglobulin deficiency?
IgA
What does S-IgA do?
Acts as first line of defense against pathogens by preventing bacterial adherence to the mucosal epithelium of the respiratory, GI, and GU tracts
What is the complement system?
A nonspecific defense system that allows for an immediate response to invading organisms
Who should be screened for complement deficiencies?
Pts with recurrent infections
Definition of viruses
Obligate intracellular pathogens composed of a central core of genetic material (DNA or RNA) surrounded by a protein coat (the capsid), which protects the nucleic acid and serves as a vehicle of transmission from one cell to another
How do viruses cause dz?
Cell lysis or by interfering with nl cell machinery to cause cellular dysfunction
Why can bacterial superinfection occur with viruses?
Impaired phagocytic capacity of virally infected macrophages or polymorphonuclear leukocytes (PMNs) rendering the host more vulnerable to bacterial infection
When can viruses be implicated in surgical diseases
Appendicitis (enterovirus)
Ulcerative colitis (CMV)
Intussusception (adenovirus)
What are the three general shapes of bacteria?
Spheres
Rods
Spirals
What is an example of a bacterial species that invades tissue?
S. pneumoniae
What are the two subdivisions of bacteria that produce toxins
Exotoxins and endotoxins
What do protein exotoxins cause?
Hemolysis of RBCs WBC death Necrosis of tissues Degradation of intercellular substances Clotting of plasma
What are some surgical diseases resulting from bacterial exotoxins?
Necrotizing fasciitis caused by C. perfringens, S. pyogenes, and S. aureus
Toxic megacolon caused by C. diff
What are endotoxins?
Macromolecular complexes of phospholipids, polysaccharide and protein, which form the outer layer of the cell wall of gram-neg bacteria
Molds
Multicellular fungi that form long filaments called hyphae and reproduce by forming spores
Yeasts
Unicellular fungi that reproduce by budding
What are the three main mechanisms by which fungi can gain access to human tissues and cause dz?
Inhalation
Inoculation of the subcutaneous tissues
Colonization of mucosal surfaces
What are other RFs for fungal infection besides being immunocompormised?
Prolonged hospitalization IV cannulae Prolonged or broad-spectrum antibiotic administration Hyperalimentation Immunosuppressive drugs Burns Trauma Malnutrition
How to determine proper selection of antimicrobial therapy?
Know
(a) the MC pathogens causing the specific infection
(b) the MOA of the selected agent
(c) the mechanisms of resistance to the selected agent
(d) potential SEs
(e) sensitivity patterns of the most common microbes in the environment
