EDKP 395 Lecture 21: EP Lecture 21
27 Mar 2018
School
Department
Course
Professor
Exercise Physiology
Lecture 21
Thermoregulation at Rest and During Exercise
Physiological Importance of Thermoregulation
- Body temperature (like pH) is regulated within very narrow limits by the physiological
control of blood flow, hormone secretion, metabolic rate, etc.
- Normal Core Body Temp. = 37 Âą 1oC (98.6 Âą 1.8oF) .
o An increase in body temperature >39.5oC (hyperthermia) may cause death due
to complications (i.e., organ failure, seizures) associated with heat stroke.
o A decrease in body temperature <35oC (hypothermia) may cause death due to
slowed metabolism, cardiac arrhythmias, loss of consciousness, reflexes and
voluntary motor control.
Contributing Factors to Heat Gain and Heat Loss to Regulate Core Temperature at ~37â
Heat inflow > heat outflow = rise in body
temp
Heat inflow < heat outflow = fall in body
temp
Wet heat loss = evaporation
Dry heat loss = the other 3
Heat Transfer ď temperature gradient allows for heat transfer (core ď skin ď environment)
1. RADIATION
⢠Requires temp. gradient b/w skin & environment.
⢠Accounts for ~60% of heat loss at rest.
⢠Transfer of heat from the surface of one object to the surface of another,
without physical contact.
⢠Under normal resting conditions, body temperature is > environmental
temperature; thus, we generally have a net loss of heat via radiation.
⢠However, when environmental temperature is > body temperature, we have a
net gain of heat via radiation.
2. CONDUCTION
⢠Transfer of heat via direct contact with a cooler object (i.e., solid, liquid or gas);
for example, heat transferred warm head to cool side of the pillow.
find more resources at oneclass.com
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⢠Rate of conductive heat transfer depends on:
1. Temperature gradient between skin and surrounding surfaces.
2. Thermal qualities of surfaces (e.g., hand feels cooler in H2O than in air
because H2O absorbs ~1,000 times more heat than air at the same
temperature
3. CONVECTION
⢠Air/H2O molecules are warmed and move away from the body and are replaced
by cooler molecules (e.g., ceiling fan).
⢠The exchange of heat via convection depends on how quickly the air/H2O
molecules surrounding the body moves.
⢠If the molecules hardly move, heat exchange is minimized and the air/H2O
insulates the body from further heat loss because of a decrease in the skin-to-
air/H2O temperature gradient.
⢠If air/H2O is constantly moving around the body, heat loss is increased because
skin-to-air/H2O temperature gradient is maintained.
4. EVAPORATION
⢠Accounts for ~25% of heat loss at rest, but is the most important mechanism of
heat loss during exercise, particularly in hot and humid environments!
⢠Heat is transferred from the body to H2O on the surface of the skin. When this
H2O gains sufficient heat, it evaporates and removes heat from the body at a
rate of 580 kcal/liter of H2O.
⢠Rate of heat loss due to evaporation of sweat from the skin surface depends on
(i.e., evaporation, not sweating, cools the skin!):
1. Surface area (SA) exposed to the environment: As SA ď, evaporative heat
loss ď
2. Relative humidity (RH) of ambient air: As RH ď, H2O vapor pressure
gradient between skin and ambient air ďŻ, which ďŻ rate of evaporative
heat loss (e.g., dry tolerable heat of Las Vegas vs. wet intolerable heat of
Singapore)
3. Convective air currents around the body: As convection ď, evaporative
heat loss ď
Hypothalamic Thermoregulation
- HYPOTHALAMUS â central coordinating center for thermoregulation. Regulates core
body temperature within 37°C ¹ 1°C
- Anterior Hypothalamus is primarily responsible for dealing with îheat stressî (i.e.,
facilitates heat loss).
- Posterior Hypothalamus is primarily responsible for dealing with îcold stressî (i.e.,
facilitates heat gain).
- Thermoregulatory Mechanisms:
1. Thermal receptors in the skin, spinal cord, and hypothalamus transmit
sensory afferent nerve information to the hypothalamus.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Body temperature (like ph) is regulated within very narrow limits by the physiological control of blood flow, hormone secretion, metabolic rate, etc. Contributing factors to heat gain and heat loss to regulate core temperature at ~37 . Heat inflow > heat outflow = rise in body temp. Heat inflow < heat outflow = fall in body temp. If the molecules hardly move, heat exchange is minimized and the air/h2o insulates the body from further heat loss because of a decrease in the skin-to- air/h2o temperature gradient. Singapore: convective air currents around the body: as convection , evaporative heat loss . Hypothalamus central coordinating center for thermoregulation. Regulates core body temperature within 37 c 1 c. Anterior hypothalamus is primarily responsible for dealing with (cid:858)heat stress(cid:859) (i. e. , facilitates heat loss). Posterior hypothalamus is primarily responsible for dealing with (cid:858)cold stress(cid:859) (i. e. , facilitates heat gain).
