Thermoregulation Flashcards
thermoregulation
body’s ability to maintain an internal temperature
Temps for humans
although humans can tolerate extremems in environmental temp, a relatively small change in core body temp ~ 4 degrees celcius leads to significant impairment of mental and physical function
core body temperature
regulated by hypothalamus, controls involuntary mechanisms that maintain internal temp of 37degrees
hypothalamus is sensitive to small temp changes - 0.1-0.5 degrees
thermal receptors
central and peripheral
central thermal receptors
hypothalamus and cortex of the brain
- blood perfusing these regions stimulates the receptors
peripheral thermal receptor
skin and visceral receptor for cold and warm temps
why does Q drop when youre warm
vasodilation for reduction of heat on SA which drives down your BP
a risk of increasing heat
not enough perfousion to the brain so you need to elevate their legs
activation of the regulatory centres in the hypothalamus reuslts in
thermal effector responses - behavioral, physiological
biological rhythms of thermoregulation
wake up
bacteria and virus on thermoregulation
immune related but need to protect the proteins in the body
what two hormones regulate the body temp
catecholamines and thyroxine
thermal balance
body temp is maintained within a narrow range through heat gain and loss
do we gain and lose heat
no we get radiated, conducted or convected, then BMR/RMR, thermogenesis, muscular activity, then we evaporate, convect, conduct and radiate
radiation (4)
transfer of heat between two objects through electromagnetic heat waves
- the body loses heat if the surrounding is cooler
- the body gains radiant heat from the sun
- represents the majority of the heat less from the body at rest (60%)
conduction (3)
transfer of heat between molecules in direct contact
- application to the skin
- 3% of the heat loss from the body at rest
convection (4)
transfer of heat with the flow of water or air across the skin
- fan blowing over the surface of the skin
12% of heat loss at rest, 20% of heat loss in water and 20% or heat gain in a hot pool
evaporation (6)
- conversion of liquid into vapour
- 150-340 sweat glands/cm^2
- 25% of heat loss at rest occurs via unnoticed insensible perspiration skin and respiratory evaporation
- 99% of sweat is water, 1% electrolyte (Na, K, Cl)
- major mechanism of heat transfer during exercise
- evaporation of sweat cools the skin (not sweat by itself), if the sweat is wiped away, the cooling effect is negated
respiratory evaporation
breathing out humidation
core temperature
36.1-37.8c
rectal temp
valid for core temp
esophagus temp
lower than rectal temp due to evaporative cooling with breathing
tympanic temp
slighly lower than rectal temp
telemetry thermal pills
expensive and more challenging to use
skin stemp
temp fluctuates under the influence of environmental conditions
heat stress
the physical work and environmental components that combine to create heat load on an ind.
factors affecting hyperthermia (4)
heat production - BMR, PA
circadian rhythms
age/gender
body size, body fat
5 modulators of hyperthermia
temp, humidity, wind hydration status fitness clothing cooling strategies
heat strain
acute physiological response and resulting thermoregulatory processes to combat heat stress
physiological response of heat exposure (3)
general peripheral dialaion - arteriovenous anastamoses
increased sweating to promote evaportation - compromised by increased humidity (heat stress index)
- 1L of vaporized sweat - 580kcals
increased ventilation (expel heat through lungs)
heat can do two things on exercise performance
increase muscle temp without increasing core temp
increase core temp
increasing muscle temp without increasing core temp (2)
increased enzyme reacion speed
increased sprint speed
increasing core temp (3)
reduce VO2max
impaired submaximal and maximal exercise performance
MVC and repeat spring bouts compromised
heat exposure in sport
start training for adaptation to happen, when you compete in the heat with a lower Q, lower blood to uslces and lower drive to exercise
kids and temp
increased SA and higher BMR, they dont sweat as much, dissipated through convection and conduction, lower Q, so harder time to get it to the skin
females and temp
dont sweat as much and more SA, subcutaneous fat adipose tissue as insulator
Q 10 effect
increase temp of enzyme by 1-2 degrees, 5-10% increase in activity
heat reduced VO2max (3)
reduced stroke volume
- dilation of vessels reduces TPR leading to decrease in MAP/preload
- decrease in blood plasma volume due to sweating
cardiovascular drift
- HR steadily increases to maintain Q and MAP
reduced utilization of oxygen due to compromised blood flow
- increased anaerobic metabolism
why does HR need to increase to maintain Q
because SV is decreased
when hr maxes after heat
continue with peripheral resistance or stop vasodilation and increased MAP, but then you accumulate a lot of heat
how to increase cycle performance in a tropical climate
physical and perceptual cooling with beverage
how to trick the receptors
keep skin temp decreased so they think its cooler than it is
exertional heat illness
spectrum of disorders that range in intensity and severity from mild CV and CNS disruptions to severe cell damage, including the brain, kidney and kidney
hyperthermia
core temp above 41, above 42 can be fatla, above 44, body begins to denature
high body temp can lead to
breakdown in nerve tissue, local hemorrhage, ultimately organ failure
minor exertional heat illness
heat cramps and heat syncope
heat cramps 2
occur in leg, arms, and abdominal muscles after several hours of strenuous exercise in heat
possible cuases - fluid electrolyte imbalance, dehydration, altered neuromuscular control
heat syncope
pooling of blood in periphery affecting CO and flow of blood to brain
seriour exertional heat illness
heat exhaustion
heat injury
heat stroke
heat exhaustion
(38.5-40c) - rapid and weak pulse
heat injury
hyperthermia accompanied by organ damage (rhabdomyolosis)
heat stroke
life threatening illness marked by CNS and multiorgan failure
goosebumps for heat
early sign of severe heat exhaustion - thermoregulation no longer working properly
acclimatization
adaptive changes that occur when an ind undergoes prolonged or repeated exposure to a stressful environment - for you to become more efficient
acclimatization to heat (5)
occurs as early as 1-4 days and completed with 10-24 days
increased plasma volume (3-27%
increased sweat distribution
reduced sweat threshold - sweating at lower temp
reduced sweat and urine electrolytes/aldosterone
fitness level and acclimatization
regular training will result in 50-60% of total physiological adaptation even if training in a cool environment
sweating at salt
you want to retain a lot more sodium to maintain muscle function - if you’re a heavy salt sweater you need more salt
4 cooling strategies
precooling/cooling during exercise
clothing
maintain hydration status
reduce warm up time
precooling/cooling during exercise
ice vests (keep it on or right after you start take it off), ice packs, mist fans, cold air more room
clothing for cooling -2
light colored clothing and hat to reflect radiative heat
well ventilated, loose fitting shirt to allow for efficient evaporation
maintain hydration status
monitor weight and urine color
epidermal microfluidic biosensor - 4
water, lactate, glucose, pH, chloride
when you lose % BW hydration 2-3 5 7 15 20
affect performance - decrease by 30% discomfort and lethargy dangerous (salivating stops) delirium, shiveled skin death
during exercise, does voluntary fluid intake fully replace fluid loss?
no, gastric emptying rate for water is 600-1200ml/hr
interind variability
3 considerations for hydration
150-250 ml every 15 mins during events
carbs and sodium in rehudration solution enhance intestinal absorption
temp does not affect absorption, but cool water will help cool the body
strength and power for hydration
alright
exercise associated hyponatermia
fluid electrolyte disorder caused by overhydration without adequate electrolyte intake - low blood sodium concetrations (<135mEq/L) leads to swelling in the brain (water into intercellular in brains because brain doesnt lose na) - swelling in brain stem can cause the dorsal ventilatory gp to be pressured
symptoms of exercise associated hyponatremia
mild - headahce, nausea, cramping
severe - seizure, coma, cardiac arrest - can be fatal
environmental factors affecting hypothermia
temp - keep up Q
water - 4-5 times faster to take heat away
wind - convection - much faster
ind factors affecting hypothermia
age - kids have larger SA, dont thermoregulate very well, lose more heat
older - dont vasoconstrict as well
gender - males dissipate more heat because females have insulators
insulating factors for hypothermia
subcutaneous fat
clothing - cotton - fibre holds wet moisture aginst your skin, not good, wool is better
3 acute physiological responses to cold exposure
general peripheral vasoconstriction
increased metabolic heat production through - non shivering thermogenesis - increased catecholamine and thyroxine release
- shivering thermogenesis - increased heat with muscle contraction
piloerection “goosebumps - subcutaneous fat mechanism to trap heat
what receptors do vasoconstrict
alpha 1
where do you send heat when youre cold
core for steady temp
decreased muslce temp without decrease in core temp (3)
slightly increased VO2 max (4degrees) - good in endurace sports but not short because of a decrease of enzyme activities
reduced fatigue
decreased core temp (3)
impaired nerve signaling (sensory and motor
force generation from type 1 muscle fibres impaired, therefore recruitment of type 2 fibres is expedited
strength and power compromised because impaired MU recruitment
after drop
in a cold environemnt you want to keep the warm blood at your core, but the as soon as he moves he vasodilates and the cold blood comes in
- cold and jerky movements
increased utilization of FT fibres for fine motor movements
decreased core temp can drop VO2 max -3
compromised muscle function (Q10), decreased HR, increase blood viscosity
reduced oxygen unloading from hemoglobin
drop of 5-6% in VO2 max for every 1 degree drop in core body temp
increased submaximal vo2 with cold -why and 2
increased metabolic rate
- higher metabolic cost for type 1 which reduces fat utilization (bonking) - more glycogen and run out of energy quicker
- coactivation of agnist and antagonist muslces
overall effect of decreased core temp
reduced submax endurance
hypothermia
core temp less than 35 degrees resulting in the loss of normal function
2
4
6
more than 6 drop in core temp
mild - max shivering
mod - ataxia, apathy, cognitive impairment (coordinated movements)
severe - unconsciousness
abnormal heart rhythm, decreased brain blood flow, death
usual fatal limit = core between 23-25
cold survival story
female fell into waterfall while skiing
- 80 min after - core 14.4
-13.7 when warming started
returned to normal function
why bring extra layers when you go down the back side of the mountain
hypoglycemic and no sun
a person is not dead until?
they are warm and dead, metabolic processes in your body is slowed so preserved, as long as they still have a heart beat, dont give up until they are warm and dead
frostbite
consequences of water crystalization within tissues that causes cellular dehydration and leads to tissue destruction, occurs when temp falls below 0
can you freeze your lungs
no, air that is -40 is humidified and warmted to body temp by the time it reaches the lungs
paradoxical undressing
towards the end stages of hypothermia ppl start taking clothes off - failure of vasoconstriction and rush out of core blood?
terminal burrowing
curl up into a tiny place, hypothesized to be instinctive behaviour to preserve heat
when does cold acclimatization occur?
first 7 days
4 effects of cold acclimatization
increased non-sivering thermogenesis
- increase in thyroxin and NE
- uncoupling oxidative phosphorylation adipose tissue increases
reduced shivering threshold
hunting reaction - intermittent peripheral vasodilation of the vessels in the hands, feet, and face for increased skin temp
increased subcutaneous fat - swimmers have economy benefits but some have to do dryland to get rid of it
eventual step of cold acclimatization
habituation to discomfort
baby withouth the blanket can still be warm to touch because
they have lots of brown adipose tissue
4 considerations for cold
dress in layers, wicking as first
20-30% heat lost through head/neck
windchill hardest on toes, fingers, nose, ears
enough glycogen store
rec outdoor jogging advice for cold
first half - run into the wind - not much sweat so no cooling ffect
second half - return with wind at back
2 layers winter camping (3)
day time - wet clothing because youre generating heat
night - dry clothes for insulation
gortec shell to get rid of
should you wear down jakets to exercise
no moisture gets in
