Page 63 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com mebooksfree.com H 8 E R mebooksfree.com
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A
P
C
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Host Defenses

mebooksfree.com mebooksfree.com mebooksfree.com Adaptive (Specific) Immunity mebooksfree.com mebooksfree.com
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CHAPTER C ONTENT S

Principles of Host Defenses
Failure of Host Defenses Predisposes to Infections
Innate (Nonspecific) Immunity
Pearls
Skin & Mucous Membranes
Self-Assessment Questions
Inflammatory Response & Phagocytosis
Practice Questions: USMLE & Course Examinations
Fever

PRINCIPLES OF HOST DEFENSES INNATE (NONSPECIFIC) IMMUNITY
mebooksfree.com mebooksfree.com mebooksfree.com isms. In addition to the physical barrier presented by skin, mebooksfree.com
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Host defenses are composed of two complementary, fre-
Skin & Mucous Membranes
quently interacting systems: (1) innate (nonspecific)
Intact skin is the first line of defense against many organ-
defenses, which protect against microorganisms in general;
and (2) adaptive (specific) immunity, which protects
the fatty acids secreted by sebaceous glands in the skin have
against a particular microorganism. Innate defenses can be
antibacterial and antifungal activity. The increased fatty
classified into three major categories: (1) physical barriers,
acid production that occurs at puberty is thought to explain
such as intact skin and mucous membranes; (2) phagocytic
the increased resistance to ringworm fungal infections,
cells, such as neutrophils, macrophages, and natural killer
which occurs at that time. The low pH of the skin (between 3
cells; and (3) proteins, such as complement, lysozyme, and
interferon. Figure 8–1 shows the role of several compo-
crobial effect. Although many organisms live on or in the
nents of the nonspecific defenses in the early response to
skin as members of the normal flora, they are harmless as
bacterial infection. Adaptive immunity is mediated by and 5), which is due to these fatty acids, also has an antimi-
long as they do not enter the body.
antibodies and T lymphocytes. Chapter 57 describes these
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A second important defense is the mucous membrane of
host defenses in more detail.
the respiratory tract, which is lined with cilia and covered
There are two main types of host defenses against
bacteria: the pyogenic response and the granuloma-
mucus up to the nose and mouth, where the trapped bacte-
tous response. Certain bacteria, such as Staphylococcus
ria can be expelled. This mucociliary apparatus, the ciliary
aureus and Streptococcus pyogenes, are defended against
elevator, can be damaged by alcohol, cigarette smoke, and
by the pyogenic (pus-producing) response, which con-
viruses; the damage predisposes the host to bacterial infec-
sists of antibody, complement, and neutrophils. These
tions. Other protective mechanisms of the respiratory tract
pyogenic bacteria are often called extracellular patho-
involve alveolar macrophages, lysozyme in tears and mucus,
gens because they do not invade cells. Other bacteria,
hairs in the nose, and the cough reflex, which prevents
such as Mycobacterium tuberculosis and Listeria mono-
cytogenes, are defended against by the granulomatous
Loss of the physical barrier provided by the skin and
response, which consists of macrophages and CD4-
mucous membranes predisposes to infection. Table 8–1
positive (helper) T cells. These bacteria are often called aspiration into the lungs.
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describes the organisms that commonly cause infections
intracellular pathogens because they can invade and
associated with the loss of these protective barriers.
survive within cells.
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