21
The Immune System: Innate and
Adaptive Body Defenses
PART 1
Innate Defenses
Surface Barriers: Skin and Mucosae
(pp. 765–766)
Internal Innate Defenses:
Cells and Chemicals
(pp. 766–773)
PART 2
Adaptive Defenses
Antigens
(pp. 773–774)
Cells of the Adaptive Immune System:
An Overview
(pp. 774–778)
Humoral Immune Response
(pp. 778–784)
Cellular Immune Response
(pp. 784–792)
Homeostatic Imbalances
of Immunity
(pp. 792–796)
Developmental Aspects of the Immune
System
(p. 796)
764
E
very second of every day, armies of hostile bacteria,
fungi, and viruses
swarm on our skin and yet we stay amazingly healthy most of the time. Te body
has evolved a single-minded approach to such foes—if you’re not with us, you’re
against us! ±o implement that stance, it relies heavily on two intrinsic defense systems
that act both independently and cooperatively to provide resistance to disease, or
im-
munity
(
immun
5
free).
1.
Te
innate (nonspecific) defense system
, like a lowly foot soldier, is always pre-
pared, responding within minutes to protect the body from all foreign substances.
Tis system has two “barricades.” Te
first line of defense
is the external body
membranes—intact skin and mucosae. Te
second line of defense
, called into ac-
tion whenever the first line has been penetrated, relies on internal defenses such as
antimicrobial proteins, phagocytes, and other cells to inhibit the invaders’ spread
throughout the body. Te hallmark of the second line of defense is inflammation.
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