a. Heat Produced by the Body. Most of the heat produced by the body comes from oxidation of the food we eat. Metabolic rate is the term for the rate at which the heat is produced. The rate at which heat is produced depends on the following:
(1) Muscular activity. Exercise increases heat production.
(2) Glandular rate. The higher a person's metabolism rate the more heat produced.
(3) Food intake. Some types of food such as foods containing sugar are burned up more quickly than other foods, thus producing more body heat.
(4) External temperature. The body reacts to environmental temperature. If the temperature of the environment (air, water) is hot, the body reacts accordingly and becomes warmer.
(5) Certain hormones. Certain hormones may increase a person's metabolic rate, thus increasing that person's heat production.
b. Heat Produced by Tissues. Tissues are responsible, in part, for heat production. Skeletal muscle tissue contractions produce heat and are an important part of the homeostatic mechanism for maintaining normal body temperature. During a skeletal muscular contraction, only 20 or 30 percent of the total energy released is used for mechanical work. The rest of the energy is released as heat. Two types of heat energy are produced: initial heat--produced by the contraction and relaxation of a muscle; recovery heat--produced after relaxation of a muscle.
c. Heat Distributed by the Blood. Blood flow plays a role in the regulation of normal body temperature because blood contains a large volume of water (an excellent heat absorber and coolant).
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