Thermoregulation Flashcards
Humans can tolerate ___ degree decline in body temp, but only a ___ degree increase
10
5
normal body temp
98 to 98.8 degrees
hypothalamus
central coordinating center for temperature regulation
how does the hypothalamus regulate temperature?
cannot “turn off” heat
thermal receptors in skin provide input
changes in blood temp that perfuses hypothalamus
thermoregulation process in heat stress
radiation
conduction
convection
evaportation
radiation
body emits electromagnetic heat waves
NO molecular contact between objects
conduction
direct heat transfer from one molecule to another through a liquid, solid, or gas
heat loss involves warming air molecules and cooler surfaces that contact the skin
convection
air or water moving across the skin
swimming
evaporation
water vaporization from skin surface to environment- major defense against over heating
heat loss by evaporation
how?
evaporation of sweat from skin exerts cooling effect
cooled skin cools blood near surface of skin
3 major factors that influence amount of sweat vaporized from skin
surface exposed to environment
temperature and relative humidity of ambiant air
convective air currents around body
What reduces evaporation?
if the sweat rolls off the body- sweat needs to evaporate in order to cool skin/blood
or
high humidity at lower temperatures
what are the two competitive CV demands when exercising in heat?
- muscles require delivery of arterial blood to sustain energy metabolism
- arterial blood diverts to periphery to transport metabolic heat for cooling skin surface; this blood cannot deliver its oxygen to active muscle.
dehydration
loss of body mass due to fluid loss
** 3-5% loss of body mass does not degrade muscular strength or anaerobic performance
Signs and symptoms of dehydration
thirst
urine color = darker
urine odor
weight loss- 1L of fluid for each pound of weight loss
fluid loss coincides with 5 factors:
- decreased plasma volume = headache
- reduced skin blood flow for given core temp
- reduced stroke volume
- increased hr
- general deterioration in circulatory and thermoregulatory efficiency in exercise
5 factors that modify heat tolerance
- acclimatization
- training status
- age
- gender
- % body fat
acclimatization
collective physiologic adaptive changes that improve heat tolerance
progressive exposure to daily heat environment with adequate hydration
acclimatization increases ____ ____, and ______,
and decreases _____ and ______
cutaneous blood flow, sweat output, exercise tolerance time
salt concentration of sweat, rectal temp per exercise workload
training status
higher fitness level respond better physiologically to sudden heat stress than untrained
known CV, immune disease, infectious disease respond poorer to physiologically heat stress
age
aging delays onset of sweating and blunts magnitude of sweating response
age has these direct effects:
modified sensitivity to thermoreceptors
limited sweat gland output
dehydration-limited sweat output
insufficient fluid replacement
gender
women tolerate thermal stress as well as men of comparable aerobic fitness and level of acclimatization
%body fat
increase insulation so more difficult to conduct heat to periphery
increased metabolic cost of weight bearing activities
fatal heat stroke occurs 3.5x more frequently in larger individuals
heat cramps
severe, involuntary, sustained muscle spasms
imbalance in body fluid level and electrolyte levels
what to do when you have heat cramps
drink water than contains salt
heat exhaustion
ineffective circulatory adjustments, depletion of extracellular fluid, principally plasma volume from excessive sweating
most common form of heat illness
signs and symptoms of heat exhaustion
weak and rapid pulse hypotensive headache dizziness general weakness
what to do when you have heat exhastion
stop exercising, move to cooler environment, get an IV
heat stroke
failure of heat-regulating mechanisms from an excessively high core temperature
signs and symptoms of heat stroke
elevated body temp greater than 40 C or 104F
CNS dysfunction
multiple organ system failure
diminished sweating, hot/dry skin
desired temp in exercise environment
65-72F
desired temp in cardiac rehab
65F
what to do when you have heat stroke
whole body immersion in cold/ice
water, fluid replacement/IV
will a 3% loss of body mass affect anaerobic performance
no
will a 3% loss of body mass affect aerobic performance
yes because there is less water to moderate temperature
what precautions should be considered in HEP
make sure that the discharge plan includes heat precautions: outdoor temp/humidity considerations; prehydrating; fluid during activity; fluid replacement; sunscreen; light colored, loose clothing; sweating; urine color; exercise early/later in day; shaded areas; mall walking; exercise facility.
