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Thermoregulation (exercise (SWEATING (maintaining hydration is important,…

- - - - gain heat from the environment
      - lose heat to the surrounding air
    - - the hypothalamus activates sympathetic cholinergic neurons innervating the cutaneous blood vessels
        
        withdrawl of tonic sympathetic input alone causes insufficient dilation
        
        vasodilation of cutaneous blood vessels
  - - - produce and secrete hypotonic sweat
    - - affected by
        
        surface area of skin exposed to the environment
        
        temp and relative humidity of ambient air
        
        greatest impact on the effectiveness of evaporative heat loss
        
        connective currents
  - - - increasing voluntary muscle contraction and metabolism
    - - shivering thermogenesis
        
        hypothalamic thermoregulatory center initiates skeletal muscle contraction
      - non-shivering thermogenesis
        
        increased heat production from brown fat
    - - the hypothalamus activates sympathetic neurons innervating the cutaneous blood vessels
      - vasoconstriction of the cutaneous blood vessels
  - - - cold exposure - human exposure to extreme cold produces many physiological and psychological challenges
- - - - heat syncope - acute: circulatory failure due to pooling of blood in the peripheral veins
      - heat cramps - acute: brief, recurrent, excruciating pain throughout the body
    - - external heat exhaustion - inadequate CO and high body temp
      - external heat injury - hypothermia and organ damage or severe dysfunction
      - exertional heat stroke - life threatening high body/brain temp and CNS dysfunction
  - - - both O2 demand of the working muscle and nervous system activity challenge the body's ability to regulate temp through this mechanism
  - - - high brain temp threatens CNS
      - further reduced gut blood flow can result in endotoxemia
  - - - ambient temp
      - humidity
      - equipment and clothing
    - - loss of fluid from ECF can result in decreased blood vol. and dehydration
        
        ECF loss can be compounded when exercising in hit environments
      - since sweat is hypotonic - sweating increases body osmolarity
    - - intense sweating for several hrs can fatigue the sweat glands
    - - maintain blood vol
      - sustain evaporative cooling
      - defense against heat stress
      - improve performance
      - DEHYDRATION
        
        reduced plasma vol
        
        increased HR
        
        reduced rate of sweating
        
        impaired thermoregulation
        
        increased fatigue
        
        reduced performance
- - - - more dilute
      - sweating begins sooner
      - 2x or 3x the vol
  - - - the effect of cooling with increasing wind velocity
        
        effect is compound with increased velocity from the exercise itself