770
UNIT 4
Maintenance of the Body
21
Table 21.2
Summary of Innate Body Defenses
CATEGORY/ASSOCIATED
ELEMENTS
PROTECTIVE MECHANISM
First Line of Defense: Surface Membrane Barriers
Intact skin epidermis
Forms mechanical barrier that prevents entry of pathogens and other harmful substances into body
Acid mantle of skin
Skin secretions (sweat and sebum) make epidermal surface acidic, which inhibits bacterial growth; also contain
various bactericidal chemicals
Keratin
Provides resistance against acids, alkalis, and bacterial enzymes
Intact mucous membranes
Form mechanical barrier that prevents entry of pathogens
Mucus
Traps microorganisms in respiratory and digestive tracts
Nasal hairs
Filter and trap microorganisms in nasal passages
Cilia
Propel debris-laden mucus away from nasal cavity and lower respiratory passages
Gastric juice
Contains concentrated hydrochloric acid and protein-digesting enzymes that destroy pathogens in stomach
Acid mantle of vagina
Inhibits growth of most bacteria and fungi in female reproductive tract
Lacrimal secretion
(tears); saliva
Continuously lubricate and cleanse eyes (tears) and oral cavity (saliva); contain lysozyme, an enzyme that
destroys microorganisms
Urine
Normally acid pH inhibits bacterial growth; cleanses the lower urinary tract as it flushes from the body
Second Line of Defense: Innate Cellular and Chemical Defenses
Phagocytes
Engulf and destroy pathogens that breach surface membrane barriers; macrophages also contribute to
adaptive immune responses
Natural killer (NK) cells
Promote apoptosis (cell suicide) by directly attacking virus-infected or cancerous body cells; recognize general
abnormalities rather than specific antigens; do not form memory cells
Inflammatory response
Prevents injurious agents from spreading to adjacent tissues, disposes of pathogens and dead tissue cells, and
promotes tissue repair; released inflammatory chemicals attract phagocytes (and other immune cells) to the
area
Antimicrobial proteins
 
Interferons (
,
,
)
Proteins released by virus-infected cells and certain lymphocytes; act as chemical messengers to protect
uninfected tissue cells from viral takeover; mobilize immune system
Complement
A group of bloodborne proteins that, when activated, lyse microorganisms, enhance phagocytosis by
opsonization, and intensify inflammatory and other immune responses
Fever
Systemic response initiated by pyrogens; high body temperature inhibits microbes from multiplying and
enhances body repair processes
Table 21.1
Inflammatory Chemicals
CHEMICAL
SOURCE
PHYSIOLOGICAL EFFECTS
Histamine
Granules of mast cells and basophils. Released
in response to mechanical injury, presence of
certain microorganisms, and chemicals released by
neutrophils.
Promotes vasodilation of local arterioles. Increases
permeability of local capillaries, promoting
formation of exudate.
Kinins (bradykinin and others)
A plasma protein, kininogen, is cleaved by the
enzyme kallikrein found in plasma, urine, saliva, and
in lysosomes of neutrophils and other types of cells.
Cleavage releases active kinin peptides.
Same as for histamine. Also induce chemotaxis
of leukocytes and prompt neutrophils to release
lysosomal enzymes, thereby enhancing generation
of more kinins. Induce pain.
Prostaglandins
Fatty acid molecules produced from arachidonic acid
found in all cell membranes; generated by enzymes
of neutrophils, basophils, mast cells, and others.
Same as for histamine. Also induce neutrophil
chemotaxis. Induce pain.
Complement
See Table 21.2 below.
 
Cytokines
See Table 21.6 (p. 790).
 
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