Transcript Thermal / Body Temperature Regulation Chapter 9

Thermal / Body Temperature
Regulation
Chapter 9
Presented by: Meghann Snyder, Kevin Lavoie,
Professor Steven Dion
Salem State college
Sport, Fitness & Leisure Studies Department
Without thermoregulation to facilitate exercise
the body would overheat and the effect would
result in death. Our core body temperature can
drop 10 degrees and the body can still survive,
but a core increase of just 5 degrees is all we
can tolerate.
 Many athletes have died of heat stress for this
reason. It is important to know how to cool off
in hot weather by understanding
thermoregulation and the best ways to make it
work to your advantage.

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Thermal Balance
 A result
of body mechanisms which:
– alter heat transfer to the shell
– regulate evaporative cooling
– adjust heat production
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Factors That Affect Heat Gain
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BMR, muscular activity, hormones, thermic effect
of food, postural changes, and environment. (Total
metabolic rate can increase 3 to 5 times from
shivering and 20 to 25 times during sustained
vigorous exercise in aerobically fit individuals.
Heat is conserved when blood is shunted into the
cranial, thoracic and abdominal cavities and
portions of muscle mass for insulation from the
shell.
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Factors That Affect Heat Loss
Radiation, conduction, convection, and
evaporation, which is most important.
 The body is cooled when internal heat
buildup causes the blood vessels to dilate
and direct warm blood to the shell.

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Hypothalamic Regulation of
Core Temperature
The hypothalamus contains the central coordination
center for temperature regulation. It initiates the
responses that keep the body from overheating or
overcooling
 Heat-regulating mechanisms are activated by either:

– Thermal receptors in the skin or,
– Temperature changes in the blood
– Free nerve endings in the skin respond to heat and cold
and relay the senses to the hypothalamus and cerebral
cortex.
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Thermoregulation in Heat
Stress: Heat Loss
The body's thermoregulatory mechanisms
primarily protect against overheating.
 Body heat loss occurs in four ways: (page 271)
– radiation
– conduction,
– convection,
– evaporation
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Heat Loss by Radiation

Our bodies are usually warmer than the
environment, so the air and the objects
around us absorb our body heat.
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Heat Loss by Conduction
Heat loss by conduction involves the direct
transfer of heat through a liquid, solid, or
gas from one molecule to another.
 The rate of conductive heat loss depends on
the temperature gradient between the skin
and surrounding surfaces and their thermal
qualities

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Heat Loss by Convection

On a breezy day, cooler air continually
replaces the warm air around the body, so
heat loss increases because the air currents
carry the heat away.
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Heat Loss by Evaporation

Water vaporization from the respiratory
passages and skin surface continually
transfers heat to the environment
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Evaporative Heat Loss at High
Ambient Temperatures
Increased temperatures reduces the
effectiveness of heat loss by conduction,
convection, and radiation.
 When temperatures exceed the body's
temperature, these mechanisms contribute
to heat gain.
 When this occurs, the only avenue to
dissipate heat is through evaporation.

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Heat Loss in High Humidity
 Sweat
evaporation depends on 3 things:
– Surface exposed to the environment
– Temperature and relative humidity of
ambient air
– Convective air currents around the body
– Relative humidity exerts the greatest impact.
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Effects of Clothing on
Thermoregulation in the Heat
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Dry clothing retards heat exchange, because if you
switch to a dry shirt you do not let evaporative cooling
take effect. (Sweating doesn’t cool you, evaporation
does.)
Heavy sweat shirts and rubber or plastic clothing cause
high humidity near the skin and also retard evaporative
cooling.
Loose clothing is recommended for evaporation since it
permits the free convection of air between the skin and
environment.
Light clothing to reflect light is recommended opposed
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Football Uniforms
Football gear causes a major barrier to heat
dissipation and seals off 50% of the skin from
evaporative cooling.
 The weight of the gear also makes the muscles
produce more heat
 Large players also have a small surface area to
mass ratio and more body fat
 Football has had many heat related deaths in the
past 20 years
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The Modern Cycling Helmet does
not Thwart Heat Dissipation
Modern helmets are lightweight,
aerodynamic, and ventilated.
 They do not keep heat from escaping
through the head.
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