Guyton and Hall
CHAPTER 74 – Body Temperature Regulation and Fever
Different factors determine the rate of heat production (the metabolic rate of the body):
1) The basal rate of metabolism of all cells of the body
2) Extra rate of metabolism caused by muscle activity, including muscle contractions
caused by shivering
3) Extra metabolism caused by the effect of thyroxine on the cells
4) Extra metabolism caused by the effect of epinephrine, norepinephrine, and
sympathetic stimulation on the cells
5) Extra metabolism caused by increased chemical activity in the cells, especially when
the cell temperature increases
6) Extra metabolism needed for digestion, absorption, and storage of food
The rate at which heat is lost is determined almost entirely by 2 factors:
1) How rapidly heat can be conducted from where it is produced in the body core to the
skin
2) How rapidly heat can then be transferred from the skin to the surroundings
Skin, subcutaneous tissues and fat of these tissues act together as a heat insulator for the
body fat conducts heat only 1/3 as readily as other tissues.
The insulation beneath the skin is an effective means of maintaining normal internal core
temperature.
Vasodilation occurs when heat needs to be conducted from the core of the body to the skin
for heat loss.
Vasoconstriction occurs when there is need for decrease of heat conduction from the core
to the skin hold onto heat.
Vasoconstriction is controlled by the sympathetic nervous system in response to
changes in body core temperature and changes in environmental temperature.
There are various methods by which heat is lost from the skin:
Radiation: causes heat loss in the form of infrared rays radiation in all directions
If the temperature of the body is greater than the temperature of the
surroundings, a greater quantity of heat is radiated from the body than is
radiated to the body.
Conduction: heat loss due to direct contact with an object
o Conduction from body surface to solid objects
o Conduction from body surface to air
Convection: the heat from the skin is first conducted to the air and then carried away
by the convection of air currents
Evaporation: in normal situations; from skin and lungs / when the temperature of the
surroundings becomes greater than that of the sin, instead of losing heat, the body
gains heat by both radiation and conduction sweating
CHAPTER 74 – Body Temperature Regulation and Fever
Different factors determine the rate of heat production (the metabolic rate of the body):
1) The basal rate of metabolism of all cells of the body
2) Extra rate of metabolism caused by muscle activity, including muscle contractions
caused by shivering
3) Extra metabolism caused by the effect of thyroxine on the cells
4) Extra metabolism caused by the effect of epinephrine, norepinephrine, and
sympathetic stimulation on the cells
5) Extra metabolism caused by increased chemical activity in the cells, especially when
the cell temperature increases
6) Extra metabolism needed for digestion, absorption, and storage of food
The rate at which heat is lost is determined almost entirely by 2 factors:
1) How rapidly heat can be conducted from where it is produced in the body core to the
skin
2) How rapidly heat can then be transferred from the skin to the surroundings
Skin, subcutaneous tissues and fat of these tissues act together as a heat insulator for the
body fat conducts heat only 1/3 as readily as other tissues.
The insulation beneath the skin is an effective means of maintaining normal internal core
temperature.
Vasodilation occurs when heat needs to be conducted from the core of the body to the skin
for heat loss.
Vasoconstriction occurs when there is need for decrease of heat conduction from the core
to the skin hold onto heat.
Vasoconstriction is controlled by the sympathetic nervous system in response to
changes in body core temperature and changes in environmental temperature.
There are various methods by which heat is lost from the skin:
Radiation: causes heat loss in the form of infrared rays radiation in all directions
If the temperature of the body is greater than the temperature of the
surroundings, a greater quantity of heat is radiated from the body than is
radiated to the body.
Conduction: heat loss due to direct contact with an object
o Conduction from body surface to solid objects
o Conduction from body surface to air
Convection: the heat from the skin is first conducted to the air and then carried away
by the convection of air currents
Evaporation: in normal situations; from skin and lungs / when the temperature of the
surroundings becomes greater than that of the sin, instead of losing heat, the body
gains heat by both radiation and conduction sweating
