or invasion by bacteria or viruses. The events of inflam-
mation dispose of microbes, toxins, or foreign material
at the site of the injury, prevent their spread to other
tissues, and prepare the site for tissue repair. The four
signs and symptoms of inflammation are redness, pain,
heat, and swelling. Inflammation can also cause the loss
of function in the injured area, depending on the site and
extent of the injury.
From the events that occur during inflammation, it’s
easy to understand the signs and symptoms. Vasodila-
tion of the arterioles causes increased blood flow to the
area. You feel this as heat and see it as redness around
the injured area. People often recognize redness as a
sign of infection. The area swells because an increased
amount of interstitial fluid has leaked out of the capil-
laries
(ed em a ).
Pain results from injury to neurons, from
toxic chemicals released by microbes, and from the in-
creased pressure of edema.
Fever
(Figure
12.7d) is an abnormally high body
temperature that occurs because the hypothalamic ther-
mostat is reset. It commonly occurs with infection and in-
flammation.
Inflammation and phagocytosis are always part of this
second line of defense in response to any material that has
crossed into the sterile body area. Inflammation causes
swelling and redness, which people often recognize as
symptoms of infection. Fever and the various antimicro-
bial chemicals are involved in only some situations.
d. Fever
Fever
is an abnormally high body temperature. Many bacterial
toxins elevate body temperature by triggering fever-causing
substances (interleukin-1) from macrophages. The high
temperature enhances the effects of interferons, inhibits growth
of microbes, and speeds up repair reactions.
b. Phagocytes, T cells, and B cells
Phagocytes
are specialized cells (neutrophils,
monocytes, macrophages) that ingest microbes
and cell debris through
phagocytosis
. Monocytes
enlarge to become macrophages, which can
migrate to infected areas or remain fixed in certain
locations.
M
7*
Neutrophil
Monocyte
Macrophage
T cells
and
B cells
are a small percentage
(5-10%) of lymphocytes that kill microbes and
certain tumor cells by releasing proteins that
destroy the target cell’s membrane.
T lymphocyte
B lymphocyte
(T cell)
(B cell)
c.
Inflammation
1.
Tissue mast cells, blood platelets, and blood basophils release
histamine
, which increases the permeability of blood vessel walls
and causes vasodilation.
2.
Increased permeability allows clotting proteins to leak from the
blood into the damaged area and isolate microbes and toxins.
3.
Release of chemicals draws neutrophils and monocytes in from the
blood (chemotaxis). These cells squeeze through the blood vessel
walls (
emigration
). They chemically attack and ingest the microbes.
4.
Macrophages die and a fluid called
pus
forms, which gets
destroyed and absorbed over several days.
Tissue injury
Chemotaxis- v /
t'tT _
Æ * '
- M
V-
v,
\ c
Microbe
Phagocytes
Emigration,
Vasodilation
'
and increased
permeability
Immune Reponses Help Protect the Body Against Disease
353
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