thermoregulatory system Flashcards
thermoregulatory system
the ability of an organism to keep its body temperature within certain boundaries
homeotherms
- constant internal body temp regardless of external stimuli
endotherms
- generate heat internally
- maintain high basal heat production
ectotherms
- depend on external heat sources
- temp changes with environment
internal (core) body temp
36.5 - 37.5 degrees celsius
optimal function 36.5 -40
hypothermia
low body temp
< 35 degrees c
lowest survivable =~ 14.4 degrees c
symptoms:
- loss of motor skills
- shivering
- decrease in blood circulation and skin temperature
moderate or severe symptoms:
- confusion/ fatigue
- loss of consciousness
hyperthermia
high body temp
> 38 degrees c
damage to cells > 42 degrees c
highest survivable =~46.5 degrees c
heat exhaustion
- faint or dizzy
- excessive sweating
- cool,clammy skin
- nausea or vomiting
- rapid, weak pulse
- muscle cramps
heat stroke
- throbbing headache
- no sweating
- red, hot, dry skin
- nausea or vomiting
- rapid, strong pulse
- may lose consciousness
measuring core body temp
thermometer probe at an accessible site
- hypothalamus
- oesophagus
- rectum
- intestinal
- oral under tongue
- ear drum
measuring skin temp
depends on:
- ambient temp
- distance from core
- skin blood flow
law of conservation of energy
energy neither created nor destroyed
only transformed from one state to another
heat production
- liberate chemical energy in food we eat
- use it to resynthesize ATP
- but process is inefficient as the energy release not equal to ATP resynthesis
- release energy in form of heat
voluntary heat production
-exercise
- 70-80% EE app
involuntary heat production
- shivering
- action of hormones
-> thyroxine
-> catecholamines
heat production during dynamic exercise
to contract the muscles
- chemical energy as ATP
- exothermic reaction convert to mechanical energy
- 25-30% converted to mechanical work (rest is heat)
oxygen consumption
VO2 as an indicator of energy expenditure (heat production)
- 1 litre of 02 consumed produces ~ 20kJ heat
- resting vo2
-~0.25 L/min
- 0.25 x 20 = 5 kJ/ min of heat
external heat gain
sky thermal radiation
solar radiation
- reflected
- air temperature and humidity
ground thermal raditaion
specific heat capacity
amount of energy required to raise the temperature of a given substance by 1 degrees c
water = 4.186 kJ/kg/c
human body tissue = 3.48 kJ/ kg/c
change in thermal energy = mass x specific heat capacity x change in temp
radiation
transfer of heat in the form of electromagnetic waves
~ 60% heat loss at rest at room temp
conduction
heat transfer from the body to an object with direct contact
~3% heat loss at rest at room temp
convection
heat transfer from one place to another by movement of fluids (air or water)
~12% heat loss at rest at room temp
skin blood flow
conduction of heat to or from air or water
dependant on skin blood flow
during exercise heat dissipation by convection is reduced
thermal gradient
heat transfer is always from higher to lower temps
evaporation
vaporisation of sweat from water to vapour
~25% heat loss at rest and ~85% during exercise
sweat evaporation
- water to vapour
-> 1g sweat = 2.41 kJ of heat
factors effecting evaporation
- air temp (humidity) = decrease
- convection currents (wind) = increase
-skin exposure (surface) = increase
sweating
sweat released from sweat glands
stimulated by sympathetic nervous system
increased SNS activity when exercising, anticipation or nervous
quantifying sweat loss and rate
sweat loss (L) = change in mass + fluid intake - urine
sweat rate (L/h) = sweat loss/ time (h)
sweat rate depends on:
- body size
- absolute VO2
- aerobic fitness
- heat acclimatisation
- environment
cold exposure: ways body loses heat
heat loss
- evaporation
-radiation
-conduction
-convection
evaporation (sweating) when core temperature >37 degrees c at rest ~25% and ~85% during exercise
radiation: ~60% heat loss
conduction (cold ground) : ~2% through sir conduction
- water causes more heat loss than air
convection (wind) : body loses ~12% of its heat
methods to reduce hyperthermia during exercise
heat acclimation
- body temp lower at given heat
- sweat rate increases and sweat more dilute
- skin blood flow reduced more blood to muscles
- blood vol increases/ not decrease
- stroke vol maintained
areas of body with greater heat loss
skull
groin
armpits
extermities
heat exhaustion treatment
cooler environment
elevate feet
saline
-oral
- intravenous
heat stroke treatment
rapidly cool body
-cold water
- ice bath
- wet towel
medical attention
hyperthermia improves sprint/ power performance
- faster nerve conduction velocity
- improvement in muscle contractile elements
- faster metabolic rate -> Q10 effect
- increased SNS activity
impairs endurance performance
impairs repeated sprint ability
Q10
temperature coefficient
measure of the rate of change of a biological/ chemical system as a consequence of increasing the temp by 10 degrees c
hyperthermia: how performance impaired
increase core temp = increase sweat rate
decrease plasma vol
decrease blood vol
decrease venous return
decrease end diastolic vol
hyperthermia: cardiovascular consequences
decrease stroke vol
increase heart rate
decrease cardiac output
decrease blood pressure
increase peripheral resistance
decrease muscle blood flow
hyperthermia: cognitive consequences
impairment in
- fatigue perception increases
- scanning vigilance
-reaction time
- attention
- visual motor tracking
hyperthermia: metabolic consequences
decrease VO2 MAX
increase anaerobic metabolism
increase muscle lactate
central fatigue
brain stops sending out neural impulses to contract muscles
sodium cations
90% of extracellular cations
pivotal role in fluid and electrolyte balance as accounts for half of osmolality of ECF
main electrolyte lost in sweat 40-50 mmol/L
replace Na+ with fluid intake
sodium ion and body water regulation
sodium ion only cation to exert significant osmotic pressure
sodium ion leak into cells and pumped out against electrochemical gradient
conc Na in ECF stable
Na+ loss through urine and presipitation
ADH
antidiuretic hormone
released from posterior pituitary
secretion stimulated by
- haemoconcentration
- increase plasma osmolarity
- decrease plasma volume
promotes water retention in kidney to dilute plasma
aldosterone
mineralocorticoid hormone
released from adrenal cortex
secretion stimulated by:
- decrease plasma sodium
- decrease blood vol
- decrease pressure
- increase plasma potassium conc
alcohol when dehydrated after exercise
increased rate of urination
lower fluid retention
reduced plasma vol
post exercise
drink to replace fluid lost in sweat
include glucose for glycogen resynthesis
inclusion of Na+ aids fluid absorption in kidneys and water retention
