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Chapter 25

Nursing HAP201 Chapter Notes - Chapter 25: Preoptic Area, Muscle Tone, Thermostat

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Nursing HAP201
Judith Card

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HAP201 Week Nine/Chapter 25: Heat and Energy Balance (pg. 964 968)
25.8 Heat and Energy Balance
Hemostasis of body temperature can be maintained only if the rate of heat loss from the body equals the
rate of heat production by metabolism
It is important to understand the ways in which heat can be lost, gained, or conserved
Heat: a form of energy that can be measured as temperature and expressed in calories.
Calorie: a defined amount of heat required to raise the temperature of 1 gram of water 1C.
Metabolic Rate
This is the overall rate at which metabolic reactions use energy
Some of this energy is used to produce ATP, and some is released as heart.
There are many factors that affect metabolic, thus it is measured under standard conditions, with the
body in a quiet, resting, and fasting condition called the basal state. The measurement obtained under
these conditions is basal metabolic rate (BMR).
Body Temperature Homeostasis
Homeostatic mechanisms can maintain a normal range for internal body temperature.
If the rate of body heat production equals the rate of heat loss, the body maintains a constant core
temperature of 37C.
Core temperature: the temp in body structures deep to the skin and subcutaneous layer
Shell temperature: the temp near the body surface in the skin and subcutaneous layer. Depending on
the environmental temp, shell temp is 1-6C lower than the core temp
If the core temp is too high, it will denature body proteins; a core temp that is too low causes cardiac
arrhythmias that lead to death
Heat Production
o The production of body heat is proportional to metabolic rate. There are several factors that
affect the MR and thus heat production
Exercise: MR may increase during strenuous exercise, as much as 15 times
Hormones: thyroid hormones are the main regulators of BMR. It increases as the levels
of the hormone rise, but this response is slow. The hormones increase BMR in part by
stimulating aerobic cellular respiration. As cells use more oxygen to produce ATP, more
heat is given off, and body temp. rises. There are other hormones that also effect BMR
(testosterone, insulin, and human growth hormone)
Nervous system: during exercise or in a stressful situation, the sympathetic division of
the ANS is stimulated. Neurons in the postganglionic area release norepinephrine and
stimulates release of epinephrine by the adrenal medullae. Both these hormones increase
Body temperature: the higher the body temperature, the higher the MR.
Ingestion of food: food ingestions causes metabolic rate to rise, due to the energy “costs”
of digesting, absorbing, and storing nutrients. This effect, food-induced thermogenesis, is
greatest after eating a high-protein meal and is less after eating carbs and lipids
Age: the MR of a child, in relation to size, is about double that of an elderly person due
to the high rates of reactions related to growth
Other factors: gender (lower MR in females, especially during pregnancy and lactation),
climate (lower MR in tropical regions), sleeping (lower), and malnutrition (lower)
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