Week 8: Thermoregulation Flashcards
What conditions is the ironman world championships in Kona (Hawaii) completed in?
Athletes swim in waters of 26 degrees, the bike across lava fields where temperatures can get close to 40 degrees, various part of the race have 60% humidity and the marathon is completed in temperatures still high and fuel depleting
K2 is the …… highest mountain in the world (and more deadly than Everest) – only a few ….. have summited and fewer still without supplemental oxygen – at its peak climbers will have only ….. atmospheres of pressure or about …..% of what you experience at sea level resulting in a …..% equivalent oxygen level (compared to …..% normally) – add to that the freezing conditions (up to -….. degrees) – it’s one of the most inhospitable and extreme environments any human will find
Second
Hundred
0.3, 30%
7.2%
21%
-50
Other than exercise where else can extreme environments be an issue?
Occupational settings eg fieldworkers (extreme dehydration, heat illness, acute kidney injury) and military personnel/fireworks are exposed to dangerous settings eg live fire fields
What is acclimation
Process of adaptation to specific environmental stressors in a controlled/artificial environment
What is acclimatisation
Process of adaptation to various environmental stressors in a natural environment
What is core temperature
Measurement representing the true deep-body temp, typically measured from the gastrointestinal tract
What is dehydration
Process of body water losses that occurs when fluid loss > intake/replacement
What is euhydration
Normal hydration level/body water content – absence of hyper or hypohydration
Thermoregulation
- The body attempts to maintain thermal homeostasis within a fairly steady range of ….. to ….. degrees celsius. Although this might be slightly higher or lower in some individuals
- Our body temperature also naturally fluctuates across the day due to …… ……
- This ……. variation can be observed in …… temps during sleep/in the morning and ……. temperatures in the afternoon
- The safe operating range for humans is typically between …… and …../…..
- When our thermoregulatory systems fail we can lose control at both …. …. This represents medical emergencies – potentially leading to death
- When we get too hot we have increased risk of heat ….. and ….. …..
- When we get too cold we begin to lose ….. and ….. control (shivering, breathing and cardiac sinus rhythm)
- Now some individuals are able to tolerate these thermal extremes some endurance athletes have been observed at temperatures in …… of ….. degrees celsius but for most people this is an extreme danger
- 36-37 degrees
- Circadian rhythms
- Diurnal, lower, higher
- Safe operating range = 35 and 38/39
- Thermal extremes
- This represents medical emergencies – potentially leading to death
- Heat exhaustion & heat stroke
- Lose reflexive and autonomic control (shivering, breathing and ….. …… rhythm)
- Excess of 42 degrees celsius
Heat balance
* Thermoregulation modulated by ….. and …… temperature receptors
* Heat gain affected by ….., ……, …… and ……
* Exercise is a major driver of heat stress, with >……% of energy released internally as heat
* Demand on cardiovascular system creates …… and …… homeostasis conflict
Central & peripheral
Metabolism, hormones, behaviour and environment
>75%
Metabolic, thermal
4 mechanisms of heat loss
Conduction
Convection
Radiation
Evaporation
What is conduction
Direct contact between objects/materials
What is convection
movement of fluid (eg liquid or air) across body
What is radiation
from electromagnetic waves emitted from our bodies (eg sun, UV, infrared
What is evaporation
conversion of liquid (eg sweat), to gas (vapor).
Our most powerful mechanism which occurs with the conversion of sweat to vapour or gas. The relative contribution of these mechanisms changes with exercise intensity and various environmental factors
Mechanisms of heat loss: relative contributions
* Evaporation is our most ….. mechanism for heat loss
* Evaporative potential …… with rising ambient temperatures
* Dry heat exchange (….., ……) ……. as ambient temperatures reaches (and exceeds) skin temperature
Why does this occur?
Powerful
Increases
Convection/Radiation, decreases
Evaporative power increases because warmer air has a greater ability to hold moisture and therefore has a greater vapour pressure gradient to allow for evaporation of liquids and cooler air
Response to hyperthermia?
We have ….. and ….. receptors that sense changes in deep body or skin temperature. Deep body temperature might be altered by exercise and muscle activity, ….., …… or …… Superficial temperature might be altered by the …… environment and …… we are wearing.
These impulses go to our …… (the …. …… at the …… centre) which takes into account various other physiological factors such as …… variation, hormones, training and …… status and it might also consider a …… or …… nervous activity, ….. …… and …….
Signals are then sent out to affect the change at either the ….. body or ….. to manipulate core temperature. We can change core temperature directly through alterations in blood flow to various regions or behaviour and muscle activity such as shivering or exercise intensity. We can also change heat at the skin by …… superficial blood vessel to promote heat …… at the skin along with …… drive to stimulate our ……. sweat glands to increase …… heat loss. Through these responses we can minimise heat gain or reduce temperature altogether to bring it back within our preferred range
Central & peripheral
Metabolism, digestion or fever
Thermal, clothing
Hypothalamus
Master regulator
Integration
Diurnal, acclamation
Sympathetic or parasympathetic, blood pressure and osmolality
Deep, skin
Vasodilating
Exchange
neural
Eccrine
Evaporative