Essentials of Anatomy and Physiology

Catabolismmeans decomposition, the breaking of
bonds of larger molecules to form smaller molecules.
Cell respiration is a series of catabolic reactions that
break down food molecules to carbon dioxide and
water. During catabolism, energy is often released and
used to synthesize ATP (the heat energy released was
discussed in the previous section). The ATP formed
during catabolism is then used for energy-requiring
anabolic reactions.
Most of our anabolic and catabolic reactions are
catalyzed by enzymes. Enzymes are proteins that
enable reactions to take place rapidly at body temper-
ature (see Chapter 2 to review the active site theory of
enzyme functioning). The body has thousands of
enzymes, and each is specific, that is, will catalyze only
one type of reaction. As you read the discussions that
follow, keep in mind the essential role of enzymes.

CELL RESPIRATION

You are already familiar with the summary reaction of

cell respiration,

C 6 H 12 O 6 O 2 →CO 2 H 2 O ATP Heat,

(glucose)

the purpose of which is to produce ATP. Glucose con-

tains potential energy, and when it is broken down to

CO 2 and H 2 O, this energy is released in the forms of

ATP and heat. The oxygen that is required comes

from breathing, and the CO 2 formed is circulated to

the lungs to be exhaled. The water formed is called

metabolic water, and helps to meet our daily need for

water. Energy in the form of heat gives us a body tem-

perature, and the ATP formed is used for energy-

requiring reactions. Synthesis of ATP means that

Body Temperature and Metabolism 401

105 ̊

104 ̊

103 ̊

102 ̊

101 ̊

100 ̊

99 ̊

98 ̊

2 hr 4 hr 6 hr 8 hr 10 hr 12 hr 14 hr 16 hr 18 hr 20 hr 22 hr 24 hr

Body temperature

Time

Hypothalamic

thermostat

Actual body

temperature

Pyrogen affects hypothalamus

Vasoconstriction, shivering

Effect of pyrogen diminishes

Sweating, vasodilation

Figure 17–1. Changes in body temperature during an episode of fever. The body tem-

perature changes (purple line) lag behind the changes in the hypothalamic thermostat

(blue line) but eventually reach whatever the thermostat has called for.

QUESTION:In this cycle of fever, why do sweating and vasodilation occur when they do?