Thermoregulation Flashcards
hypothalamus
- temperature “HQ” for the body in the brain
- controls involuntary mechanisms to keep core temp 36.1-37.8C
- very sensitive to small degree changes
- behaviour or physiological forms of thermoreg
thermoregulation input
- hypothalamic temperature and other deep temperature contribute to core temp»_space; thermal error signal
- pyrogens, heat acclimatization and exercise»_space; set temp > thermal error signal
behavioural thermoregulation
The maintenance of a constant body temperature by means of basking, sheltering, shivering, etc.
- thermal comfort and effector signal head to the brain
physiological thermoregulation
effector signal for heat production > skeletal muscles
effector signal for sweating, vasodilation > arteries, sweat glands
effector signal for vasoconstriction > veins, arteries
thermal receptors
central: hypothalamus and cortex receptors in brain
peripheral: skin receptors for hot and cold (shell)
deep (core): in abs and great veins can sense internal changes
thermal effector responses to heat
- general peripheral vasodilation
- increase sweating to promote evaporation
- conscious acts (remove clothes, seek shade)
- acclimatation
thermal effector responses to cold
- general peripheral vasoconstriction
- shivering and non-shivering thermogenesis (increase metabolic heat production)
- goose bumps (piloerection)
- conscious acts (move into sun, put on more clothes)
- acclimatation
core temperature
rectal, tympanic (ear), oral, telemetric thermal pills
- rectal and GI are best (expensive)
- oral: lower than rectal (breathing and respiratory cooling)
skin temp: skin thermistors
- accuracy depends on location, exposure, movement
thermal balance
heat loss/gain mechanisms need to be balanced to prevent pushing too far from 37C
gain: environmental (radiate, convection, conduction) and metabolic (BMR, thermogenesis, muscular activity)
heat loss: evaporation, conduction, convection, radiation
radiation
transfer of heat btwn 2 objects via energy waves (electromagnetic)
- heat goes from warm object to cold object
- body can gain heat radiantly from the sun
- 60% of heat loss at rest
conduction
transfer of heat btwn solid, liquid, gas molecules or different temp that are in direct contact
- ex: ice lying on hot stove
- related to temperature differences btwn objects
- 3% heat loss at rest
convection
transfer of heat from one place to another by the movement of air/fluid across the skin
- related to velocity and temperature of the air/fluid flow
- 10% of heat loss at rest
evaporation
transfer of heat when a liquid changes to a gas or vapour
- best cooling mechanism (25% heat loss at rest, room temp)
- latent heat of vaporization
- air humidity determines if heat > gas vs vapour
- dripping sweat is not evaporation (1L = 580cal)
heat exchange factors
major determining factors for how well heat moves btwn body and environment
- thermal gradient
- relative humidity
- air movement
- degree of direct sunlight
- clothing worn
important degrees
42+ C = seriously impaired (heat stroke, brain lesions)
40-43C = exertional heat stress
38-41C = effective fever in health (fever in exercise)
32-35C = mild hypothermia (the “-umbles”)
29-34C = impaired functioning
26-30C = severe hypothermia
less than 28C = lost functioning
measuring heat stress
wet bulb globe temperature (WBGT)
- measure of heat loss in direct sunlight
- temperature, humidity, wind speed, sun angle, cloud cover
body temperature during exercise in heat
- lower intensity means for lower core temp
- environmental conditions increase in intensity makes it harder to remain same core temp so it will increase
- “uncompensable zone” when core temp rapidly increases
cardiovascular system in the heat
- blood flows to skin rather than muscles
- vasodilation to skin = less CBV = less venous return = less SV
- sweating decreases BV and SV thus a less Q (more CV strain)
- higher HR and lower preload = smaller CO
- Qmax less = VO2max less
Spectrum of EHIs
mild: heat cramps (mild dysfunction)
mild/mod: syncope (multisystem, moderate dysfunction)
mod: heat exhaustion (multisystem, severe dysfunction)
mod/severe: heat injury (multisystem damage)
severe: heat stroke (multisystem damage)
cardiovascular drift
gradual increase in HR during prolonged steady-state exercise
- rising body temp (sensed by hypothalamus)
- vasodilation of skin leads to less central blood volume
- dehydration = less BV = less preload = less SV = higher HR to maintain Q
Q = SV x HR (if one decreases the other increases to maintain Q)
importance of fluid ingestion
- Q will increase as hydration does
- SV is higher with better hydration
- HR is lower with better hydration
- can combat CV drift
factors affecting response to heat stress
acclimatization - adjustments made to repeated exposure
fitness level - better trained = better thermoregulators
body composition - more fat = more insulin
hydration levels -
heat acclimatization
in as early as 1-4 days, full acclimatization in 10-24 days
circulatory: more plasma volume = higher Q (less CV strain)
and more blood flow from periphery to core
sweat: start to sweat sooner, increase sweat rate w/o electrolytes lost
hormonal: altered ADH (urine) and aldosterone (electrolytes in kidney) (they tell kidney how much fluid to take)
- training will do 50-60% of the adaptations
fluid ingestion
in most cases plain water is the best, except for endurance (>1hr) events where CHO drinks (2.5-10%) are recommended
- determined by gastric emptying and intestinal absorption
- Na, Cl, K are sweat electrolytes
- hyponatremia ( too much water intake dilutes Na (action potentials))
exercise in the cold
hypothermia is less common in exercise except for in swimmers.
frost bite is bigger concern - treat with proper clothing, watch windchill, stay hydrated
physiological responses to cold
non shivering thermogenesis (increase in SNS release EP = increase cell metabolic heat production = increase EE) (adrenaline from adrenal glands and thyroid boost heat production)
involuntary shivering: CNS attempt to increase metabolic het production = increase EE
goose bumps (add insulating layer, better in furry animals)
immersion diuresis (submerged)
cold water immersion
cold shock phenomenon: gasp, hyperventilate increase VE 600-1000% (keep head up, do not panic; 1st min is critical)
cold incapacitation: 10 minutes of meaningful movement, drown after if w/o PFD
hypothermia: ~1hr before lose LOR depending on body comp
acclimatization to cold
- initial effect over 7 days
- decrease in skin temp of when to start shivering
- increase non shivering thermogenesis (thyroxine hormone)
- cold induced vasodilation of hands and feet (less constriction)
- increased amounts of brown adipose tissue (BAT)
brown fat
a dark-colored adipose tissue with many blood vessels, involved in the rapid production of heat in hibernating animals and human babies.
