Thermoregulation Flashcards
What is temp regulation related to?
metabolic heat production
What is homeosthermic temp (average temp) ?
Range: 35.5-37.7
Average: 37
Maintain heat balance
Mass balance (input=output)
Sources of input:
-External (from the environment)
-Internal (metabolism sufficient to maintain temp)
Heat Exchange Mechanisms
-Radiant 60%(given off by anything greater than 0)
-Conductive 3% (touching)
-Convection 12% (air currents)
-Evaporation 25% (heat loss in water at same temp as air is 2-4x greater)
insensible evaporation
What causes variation on body temperature?
PA level
Emotions
Eating
Environmental conditions
If ambient temperatures are above…
If ambient temperatures are below…
=Heat gain>heat loss
=Heat gain less than heat loss
What controls autonomic temp?
Hypothalamus determines appropriate response (acts as a thermostat and can detect changes of 0.1-0.5)
What do thermoreceptors do and where are they located?
monitor change in body temp
send info to the skin (peripheral) and hypothalamus (central)
Deep neural receptors in abdomen and great veins that can sense temp changes
What are the mechanisms that regulate body temp?
1) adjust blood flow distribution
2) sweating
3) Increase metabolism
4) Hormonal regulation
1) Adjust blood flow distribution
Convective heat loss/gain through blood distribution
Cutaneous vessels can either
-Gain or lose heat to or from the environment
Change diameter through neural control
Some local vasodialtion
Decrease temp = increase sympathetic neurons = vasoconstriction = more blood to core
Increase temp = sympathetic cholinergic neurons innervate cutaneous vessels = vasodialtion = blood to peripheral
2) Sweating
Heat lost though skin by evaporation
increase core temp = sympathetic cholinergic neurons stim sweat glands (secrete hypotonic sweat)
Evaportation is affected by
-Exposed skin area
-Temp and humidity(greatest impact - increase = decrease evap)
-Convective currents
3) Increase Metabolism
Increase heat production
Unregulated
-increase voluntary muscle contraction (moving)
Regulated- shivering (hypothalamic thermoregulatory center initiates contractions
-Non-shivering thermogenesis (increased heat from brown fat)
4) Hormonal Regulation
Increase release of epinephrine and norepinephrine increase heat production
Cold exposure thyroid releases more thyroxine to elevate RMR
Cold exposure = many physiological and psychological challenges
Thermoregulation and Exercise
Exercise in the cold
Body loses heat 2-4x faster in water at the same temp of air due to conduction
Metabolic heat generated by muscular activity contributes to thermoregulation during cold stress
Better adaptations to heat than cold
Wind Chill
The affect of cooling associated with increase velocity
Effects increase with increase exercise velocity
Thermal Balance in Response to heat
Peripheral vasodilation
Increase sweating
Conscious acts (choosing to wear lighter clothes)
Acclimatization
What is thermal effector response?
Regulation of heat loss and heat gain to control body temp at rest during exercise and in response to the environment
Exercise in heat
core temp above 42 degrees can be fatal
Core temp above 44 proteins start to denature
Increase in core temp = breakdown of nervous tissue, local hemorrhage and organ failure
What is hyperthermia?
core temperature above 41 degrees
How is fluid loss determined?
Pre-exercise weight- post exercise weight
1kg = 1L of fluid lost
What is sweat rate?
Change in weight (fluid loss)/exercise time
What is Cardiac Drift?
Gradual increase in HR during prolonged exercise especially in heat even with no increase in intensity
Increased core temp=increased blood flow to the skin
Blood volume is reduced
Decrease SV increase HR to compensate for constant Q
Considerations for elderly and children in heat
reduced circulation, efficiency, degenerative diseases
Higher rate of heat, lower sweat, lower heat transfer
What are gender differences in heat?
Women have slower sweating response, decrease sweat volume, increase sweat glands,
Larger surface area allows for better cooling
Acclimatization in the heat
Take 10-24 days for full
increase circulation
increase sweat response
Practical considerations for exercise in the heat
Avoid prolonged exercise Stay hydrated wear light colors be conscious of sign and symptoms reduce expectation acclimatize
Exercise in the cold
lose heat through radiation, conduction, convection, evaporation
What is hypothermia?
core below 35 degree
What are physiological response to cold temp?
1) Non-shivering thermogenesis increase in sympathetic stim. release of epinephrine and thyroxine 2) Peripheral vasoconstriction 3)Involuntary shivering 4) Goose bump
Gender differences in the cold
Women increased peripheral vasoconstriction during the cold. Larger body surface, less muscle mass.
Advantages: increased body fat aides in insulation
Cold acclimatization
Starts in 7 days. complete in a month
Increase non-shivering thermogenesis
Intermittent vasodialtion of the vessels
Practical consideration of exercise in the cold?
Dress in layers
Consider wind chill
First half into the wind
Use head like a radiator
Wicking and Evaporation
Wicking sweat away form the skin reduces cooling
