Thermoregulation Flashcards
Explain how the hypothalamus maintains thermal balance (heat)
Negative feedback loop
1. increased blood temp (small as 0.01C)
2. afferent signals give input to hypothalamus
3. hypothalamus triggers quick response
- vasodilation of blood vessels
- increasing sweat/evaporative heat loss
*quickly trigger reflexes to help conserve or eliminate body heat *
What are physical factors that contribute to heat loss?
convection, evaporation, conduction, radiation
What are physical factors that contribute to heat gain?
BMI, muscular activity, hormones, thermic effect of food, postural changes, enviroment
How does the circulatory system adjust during temperature changes?
- venous blood vessels dilate to divert warm blood to skin (HR & Q increase) rest*
- lower SV so higher HR *submaximal intensity
- maximal Q decreases
- maintaining skin/muscle blood flow require other tissues to compromise blood supply
How is fluid loss during hot-weather exercise calculated?
for every 1pound of weight loss, drink 450mL
What is the purpose of fluid replacement & pre-exercise hydration?
purpose:
1. to maintain plasma volume so circulation & sweating can occur
2. increase blood flow to skin for effective cooling
3. most effective defense against heat stress
What factors maintain cutaneous blood flow & BP during exertion in heat?
dilation of blood vessels
How does cardiac output respond during hot-weather physical activity?
maximal Q decreases (because the increase in HR is not greater than the decrease in SV)
How does heart rate respond during hot-weather physical activity?
increases, to adjust for the decrease in SV
How does stroke volume respond during hot-weather physical activity?
decreases, because blood is getting directed to skin instead of the core
How does acclimatization modify heat tolerance during physical activity?
improves exercise capacity with less discomfort upon subsequent heat exposure
(occurs during 1 week of heat exposure)
- improved cutaneous blood flow
- effective Q distribution
- lower threshold for start of sweating
- increased sweat output
- lower Na concentration of sweat
- lower skin/core temp & HR during exercise
How does training modify heat tolerance during physical activity?
- increases sensitivity/capacity of sweat response
(sweating begins at lower temp) - greater cutaneous blood flow at given internal temp or % of VO2 max
How does age & gender modify heat tolerance during physical activity?
age: no differences (young, middle-aged)
children –> sweat less & maintain higher core temp during heat stress (despite more# sweat glands)
- intensity effort should decrease & longer time for acclimatization
gender:
Women sweat less than men
- sweat at higher skin/core temp & produce less sweat (even after acclimatization)
- smaller & relatively larger body surface area per unit mass (favours heat dissipation)
why? greater use of circulatory mechanisms for dissipating heat
How does body fat modify heat tolerance during physical activity?
fat increases insulatory capacity of body & limits conduction to periphery
- heat capacity of fat > muscle
- smaller SA to body mass ratio
(limits effectiveness of evaporation)
What are the symptoms, causes, and treatments for heat exhaustion?
cause: ineffective circulatory adjustments with depletion of extracellular fluid (plasma volume) from excessive sweating
symptoms:
- nausea, chills, goose bumps, headache
What are the symptoms, causes, and treatments for heat stroke?
cause: SERIOUS, failure of heat-regulating mechanisms from excessively high core temp
symptoms:
cessation of sweating, confusion, LOC
What are the physiological adjustments to cold stress?
Vascular:
- peripheral blood vessels constrict to redirect warm blood to core
Muscular:
- PA best defence against cold (can sustain core temp as cold as -30C)
- shivering (metabolic heat) 4-5fold increase in heat production
Hormonal:
- Epi/norepi increase heat production
- thyroxine increases resting metabolism (prolonged cold stress)
What effect does airway remodelling due to exercise in cold air have?
prolonged exposure to cold can cause inflammation & remodelling of airways
How high does metabolism become in elite athletes during intense aerobic activity?
20-25x above resting levels
What is conduction?
direct heat transfer from one molecule to another (either gas, liquid, solid)
ex. moving from deep tissues to cooler surfaces
(has to be physically touching?)
What does conduction depend on?
- temperature gradient between skin & surrounding temperature
- thermal qualities of the surface
What is convection?
transferring heat by motion of a gas or liquid across a heated surface
ex. heat is exchanged with the air passing over skin
greater movement = greater rate of exchange
What is radiation?
heat waves emitted, that may be absorbed by a cooler body
What are the 2 primary methods for eliminating excess body heat?
radiation & convection
