Theromregulation

Theromregulation

Measurement of Body Temperature
1. Mean body temperature = (Core Temp X 0.6) x (Surface Temp X 0.4)
2. Core Temp - Rectum, Eardrum, Esophagus
3. Surface Temp - Skin
Regulation of Body Temperature - Hypothalamus
1. 2 main mechanisms
  1. 1. Thermal receptors in the skin provide peripheral input to the hypothalamus
  2. 2. Temperature changes in blood perfusing the hypothalamus directly stimulate
Responses to HEAT
1. Circulatory
  1. Increased HR and CO
  2. Arterial & Venous Blood vessels dilate to divert warm blood to the surface
  3. 25% of CO passes through the skin which greatly increases conductance and increases heat loss to the environment via radiation
2. Hormonal
  1. Release of ADH to conserve water, used for sweat = cooling
  2. Release of aldosterone, maintains Na+ and also direct effect on sweat glands; reducing their osmalrity = Preservation of electolytes
3. Evaporation
  1. Sweating is response to heat stress
  2. After 30 mins, sweat related to work load
  3. Large blood flow to skin is coupled with evaporation cooling, which cools the blood and returns to deeper tissues
4. Radiation, Conduction, Convection, * Evaporation *
Responses to Cold
1. Circulatory
  1. Stimulation of skin receptors constricts peripheral blood vessels
  2. Vasoconstriction reduces flow of warm blood to the surface and directs it to the warmer core
  3. Skin temps decrease, which optimizes the insulator benefits of skin and subcutaneous fat
2. Muscular Activity
  1. Shivering generates a significant amount of metabolic heat
  2. Physical activity; Exercise energy metabolism can sustain constant core temps of -30
3. Hormonal Output
  1. Epinephrine and NE account for basal heat production
  2. Thyroxine release is increased which increases metabolism and therefore heat production
Responses to Exercise
1. heat
  1. 1. Oxygen delivery to muscles must increase to provide muscles 2. Also peripheral blood flow must increase to transport metabolic heat out the body.
  2. CO Remains the same, However SV drops in proportion to fluid loss. HR rises to compensate. But overall CO drops as HR cannot match decline in SV
  3. Vasoconstriction of SVB and renal tissuse, directs blood flow elsewhere. can potentially lead to kidney and liver complications, if prolonged
  4. Prolonged exercise in heat: excessive fluid loss = Dehydration = Drop BV = Drop in SV/CO = Decrease 02 supply = Fatigue
  5. Prolonged sweating can = sweat gland fatigue = impaired temperature regulation
2. Cold
  1. Physiological strain depends on 1- Environmental temp. 2 - Level of energy metabolism 3- Resistance to heat flow by body fat
  2. Water conducts heat 2/4 times faster than air.
  3. Can lead to hypothermia
  4. Swimming at submaximal pace 18C requires 500m more 02. This is down to added energy cost of shivering to keep warm
  5. outdoor activities lead to cold injuries. Large vasoconstriction reponse can lead to reduced blood flow so much that frostbite can occur.
3. Acclimatisation
  1. Achieved through training in hot conditions. 100 mins of moderate exercise most efficient way. Rapidly occur in 2 weeks. Benefits also lost rapidly.
    1. Lower core temp. Increased BV. Reduced Salt loss. Earlier onset of sweating. Increased shock proteins
  2. Harder to achieve but still possible. 2 weeks also.
    1. Reported that female divers have increased metabolic rates (25%) which allows them to tolerate colder temperatures 10C colder.
    2. Maintenance of hand and foot temperatures, decreasing the risk of frostbite. Also a lower body temp before the onset of shivering

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	Created by Alex Cooke almost 9 years ago