Lab 9: Thermoregulation Flashcards
define thermoregulation
the physiological and behavioral responses by which organisms regulate body temperature
how do endothermic species thermoregulate?
endothermic species (mammals) warm their tissues from metabolic heat production
how do ectothermic species thermoregulate?
ectothermic species (reptiles & amphibians) depend on the external environment for warming
changes from normothermia that can be fatal
reductions in core temp of 10 degrees celsius or elevations in core temp of 5 degrees celsius
difference between core temperature and shell temperature
there is a thermal gradient from deep body temperature to skin temperature
common measures of core temperature in a clinical setting
rectal, oral, axillary, tympanic or temporal temperatures
common measures of core temperature in a research setting
(clinical setting sites) and also esophageal and gastrointestinal temperature
how is esophageal temperature measured?
by inserting a thermistor through the nose into the esophagus
how is gastrointestinal temperature measured?
using an ingestible pill sensor
normal core temperature
37 degrees C (98.6 degrees F)
factors that cause small variations in normal core temperature
circadian rhythm, menstrual phase in females
when does stage 1 hypothermia occur?
at or below a core temp of 35 degrees C
signs of hypothermia (stage 1)
shivering, loss of limb movement, blueness in the skin, confusion
at what temperature is hypothermia deemed a medical emergency?
at or below 32 degrees C
at or below 32 degrees celsius, what additional signs may present?
hallucinations, delirium, excessive sleepiness
what can happen at temps as low as 24-26 degrees C?
respiratory or cardiac arrest —> subject may become comatose and death usually follows
physiological responses to increases in core temp
increases in sweat rate, heart rate, and breathing rate
if core temp continues to increase without correction, what signs can present?
nausea, dizziness, weakness, and fainting
at what core temps do heat exhaustion and heat stroke occur?
temps exceeding 40 degrees C
at what high core temp is death nearly certain?
45 degrees C
what are mechanisms of heat transfer dependent on during exercise?
the external environment
mechanisms of heat loss from the body when the environment is cooler than the body
radiation, conduction, convection
change in mechanisms of heat loss from the body as environmental temperature increases
importance of evaporative heat loss increases
once environmental temperature exceeds body temperature, what happens to the thermal gradient for conduction, convection, and radiation? how does the body lose heat?
the thermal gradient for these three is reversed and the body gains heat through these mechanisms; the ONLY mechanism for heat loss from the body is evaporation
as humidity and ambient temperature increase, what happens to the capacity of evaporative heat loss?
capacity of evaporative heat loss decreases
at what humidity and temperature is evaporative heat loss minimal?
humidity near 100% and ambient temp is 30 degrees C or above
what does the Wet Bulb Globe Temperature (WBGT) index address?
if a given environment is safe/dangerous to exercise in
what measurements does the WBGT index take into account? what are they each influenced by?
Tw (wet bulb temp): influenced by level of humidity
Tg (black globe temp): measures radiant heat
Td (dry bulb temp): actual ambient air temp
WBGT equation
WBGT = 0.7(Tw) + 0.2(Tg) + 0.1(Td)
what does an efficiency of 20% mean for a cyclist?
80% of energy transformation is lost as heat
what happens to heat produced during metabolism that is not lost?
stored in body tissues and raises body temperature
quantify the body heat gained during exercise
body heat gain during exercise = heat produced - heat loss
what does specific heat of the body refer to?
the amount of heat required to raise body temp by 1 degree C
specific heat in humans
0.83 kcal/kg body mass
equation to find heat required to raise body temperature by 1 degree C
amount of heat (kcal) = 0.83 kcal/kg * body mass (kg)
difference between dehydration and reduction in plasma volume
dehydration refers to the loss of body water, whereas changes in plasma volume are influenced by alterations in total body water AND the distribution of water between the intravascular, interstitial, and intercellular compartments
4 primary mechanisms of body water loss during exercise
1) sweat loss
2) metabolic mass loss (MML)
3) respiratory water loss (RWL)
4) urinary water loss (UWL)
primary mechanism for most water loss during exercise
sweat loss
for body mass change following exercise to equal sweat loss, what assumption is made?
sweat loss is the only mechanism of water loss
metabolic mass loss (MML) results from
O2/CO2 exchange
respiratory water loss results from
ventilation
how can MML, RWL, and UWL be calculated?
using formulas
sweat loss =
total body mass loss - MML - RWL - UWL
at a constant absolute intensity, time to exhaustion is ____ under heat stress
shortened
factors influencing the reduction in performance under heat stress
duration, intensity, environmental conditions, heat acclimatization status
potential mechanisms that reduce performance in heat
1) brain reduces neuromuscular drive at high core temps to reduce metabolic heat production and prevent excessively high temps
2) core temps above 40 degrees C cause central fatigue
3) cardiovascular instability (increased HR, decreased stroke volume, descreased blood volume, increase skin blood flow)
4) accelerated glycogenolysis and increased free radical production
difference between acclimatization and acclimation
acclimatization refers to adaptions resulting from changes in the natural environment whereas acclimation refers to adaptations resulting from exposures produced in a controlled lab setting
example of heat acclimatization
exercise in hot summer heat over several days
example of acclimation
exercise performed in the lab under environmental conditions identical to the previous example
regular bouts of exercise is a hot environment promote heat acclimatization/acclimation in ___ days
7-14
physiological adaptations of heat acclimatization/acclimation
increased plasma volume, earlier onset of sweating, higher sweat rate, reduced salt loss in sweat, reduced skin blood flow, increased synthesis of heat shock proteins
what do the physiological adaptations of heat acclimation lead to?
reduced heart rate and lower core temp during exercise
how does an increase in plasma volume help with acclimation?
increases sweating capacity, increase stroke volume, maintains blood volume, and allows the body to store more heat without an increase in core temp
how does earlier onset of sweating help during heat acclimation?
allows the body to dissipate heat more quickly and reduce heat storage
how does reducing the amount of sodium lost help during heat acclimation?
minimizes the electrolyte loss
purpose of heat shock proteins during heat acclimation?
protest cells from heat damage
describe the procedure generally
