the body temperature is returning to normal. The
sequence of temperature changes during a fever is
shown in Fig. 17–1.
You may be wondering if a fever serves a useful pur-
pose. For low fevers that are the result of infection, the
answer is yes. White blood cells increase their activity
at moderately elevated temperatures, and the metabo-
lism of some pathogens is inhibited. Thus, a fever may
be beneficial in that it may shorten the duration of an
infection by accelerating the destruction of the
pathogen.
High fevers, however, may have serious conse-
quences. A fever increases the metabolic rate, which
increases heat production, which in turn raises body
temperature even more. This is a positive feedback
mechanism that will continue until an external event
(such as aspirin or death of the pathogens) acts as a
brake (see Fig. 1–3). When the body temperature rises
above 106°F, the hypothalamus begins to lose its abil-
ity to regulate temperature. The proteins of cells,
especially the enzymes, are also damaged by such high
temperatures. Enzymes become denatured, that is,
lose their shape and do not catalyze the reactions nec-
essary within cells (see Fig. 2–9). As a result, cells
begin to die. This is most serious in the brain, because
neurons cannot be replaced, and cellular death is the
cause of brain damage that may follow a prolonged
high fever. The effects of changes in body temperature
on the hypothalamus are shown in Fig. 17–2.
A medication such as aspirin is called an anti-
pyreticbecause it lowers a fever, probably by affecting
the hypothalamic thermostat. To help lower a high
fever, the body may be cooled by sponging it with cool
water. The excessive body heat will cause this external
water to evaporate, thus reducing temperature. A very
high fever requires medical attention.METABOLISM
The term metabolismencompasses all of the reac-
tions that take place in the body. Everything that hap-
pens within us is part of our metabolism. The reactions
of metabolism may be divided into two major cate-
gories: anabolism and catabolism.
Anabolismmeans synthesis or “formation” reac-
tions, the bonding together of smaller molecules to
form larger ones. The synthesis of hemoglobin by
cells of the red bone marrow, synthesis of glycogen by
liver cells, and synthesis of fat to be stored in adipose
tissue are all examples of anabolism. Such reactions
require energy, usually in the form of ATP.400 Body Temperature and Metabolism
BOX17–2 COLD-RELATED DISORDERS
slurred speech, drowsiness, and lack of coordina-
tion. At this stage, people often do not realize the
seriousness of their condition, and if outdoors (ice
skating or skiing) may not seek a warmer environ-
ment. In progressive hypothermia, breathing and
heart rate slow, and coma and death follow.
Other people at greater risk for hypothermia
include the elderly, whose temperature-regulating
mechanisms are no longer effective, and quadriple-
gics, who have no sensation of cold in the body. For
both of these groups, heat production is or may be
low because of inactivity of skeletal muscles.
Artificial hypothermia may be induced during
some types of cardiovascular or neurologic surgery.
This carefully controlled lowering of body tempera-
ture decreases the metabolic rate and need for
oxygen and makes possible prolonged surgery
without causing extensive tissue death in the
patient.Frostbite is the freezing of part of the body.
Fingers, toes, the nose, and ears are most often
affected by prolonged exposure to cold, because
these areas have little volume in proportion to their
surface.
At first the skin tingles, then becomes numb. If
body fluids freeze, ice crystals may destroy capillar-
ies and tissues (because water expands when it
freezes), and blisters form. In the most severe cases
gangrene develops; that is, tissue dies because of
lack of oxygen.
Treatment of frostbite includes rewarming the
affected area. If skin damage is apparent, it should
be treated as if it were a burn injury.
Hypothermiais an abnormally low body tem-
perature (below 95°F) that is most often the result
of prolonged exposure to cold. Although the
affected person certainly feels cold at first, this sen-
sation may pass and be replaced by confusion,