Thermoregulation
Objectives <ul><li>Describe the thermoregulatory center and its functions. </li></ul><ul><li>Explain the mechanisms of hea...
Body Temperature <ul><li>Shell temperature: </li></ul><ul><ul><li>Temperature closer to skin </li></ul></ul><ul><ul><li>Or...
Heat Production <ul><li>Exergonic reactions: </li></ul><ul><ul><li>Oxidation and ATP use. </li></ul></ul><ul><li>Most heat...
Thermoregulatory Center <ul><li>Hypothalamus: </li></ul><ul><ul><li>Preoptic area neurons: hypothalamic thermostat: </li><...
Thermoregulatory Center <ul><li>Heat-losing center: </li></ul><ul><li>Activates heat losing mechanisms: </li></ul><ul><ul>...
Thermoregulatory Center <ul><li>Heat-promoting center: </li></ul><ul><li>Activates heat generating mechanisms: </li></ul><...
Thermoregulatory Center <ul><li>Hypothalamus: </li></ul><ul><li>Peripheral thermoreceptors: </li></ul><ul><ul><li>Temperat...
Mechanisms of Heat Transfer <ul><li>Radiation: </li></ul><ul><ul><li>Infrared radiation. </li></ul></ul><ul><li>Conduction...
Heat Exhaustion <ul><li>Acute heat injury due to dehydration. </li></ul><ul><li>Heat-loss center stimulated. </li></ul><ul...
Heat Exhaustion <ul><li>Symptoms: </li></ul><ul><ul><li>Headache </li></ul></ul><ul><ul><li>Nausea </li></ul></ul><ul><ul>...
Heat Stroke <ul><li>Core rectal temperature approaches 41 o C </li></ul><ul><li>2 types: </li></ul><ul><li>Individuals wit...
Heat Stroke <ul><li>Renal and splanchnic vasoconstriction. </li></ul><ul><li>Peripheral blood flow decreases. </li></ul><u...
Heat Stroke Complications <ul><li>Rhabomyolysis </li></ul><ul><li>Multiple organ failure: </li></ul><ul><ul><li>Cardiac </...
Heat Stroke Treatment <ul><li>Drop core temperature by 0.2 o C/min </li></ul><ul><li>Institute evaporative cooling methods...
Exercise <ul><li>Maximum exercise, heat production can be 10-20 times resting. </li></ul><ul><li>Highest temperatures occu...
Exercise Acclimatization <ul><li>Exercise in the heat for two weeks at a safe intensity. </li></ul><ul><li>Plasma volume i...
Hypothermia <ul><li>Core temperature below 95 o F. </li></ul><ul><li>Gradual loss of mental and physical activity. </li></...
Hypothermia <ul><li>If core temperature remains above 90 o F, recovery is good. </li></ul><ul><li>If core temperature fall...
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termoregulation

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termoregulation

  1. 1. Thermoregulation
  2. 2. Objectives <ul><li>Describe the thermoregulatory center and its functions. </li></ul><ul><li>Explain the mechanisms of heat transfer. </li></ul><ul><li>Explain the pathophysiological mechanisms involved in temperature disorders. </li></ul>
  3. 3. Body Temperature <ul><li>Shell temperature: </li></ul><ul><ul><li>Temperature closer to skin </li></ul></ul><ul><ul><li>Oral temperature </li></ul></ul><ul><ul><ul><li>36.6 o -37.0 o C (97.9 o -98.6 o F) </li></ul></ul></ul><ul><li>Core temperature: </li></ul><ul><ul><li>Most important temperature </li></ul></ul><ul><ul><li>Temperature of “core” (organs in cranial, thoracic and abdominal cavities) </li></ul></ul><ul><ul><li>Rectal temperature </li></ul></ul><ul><ul><ul><li>37.2 o -37.6 o C (99.0 o -99.7 o F) </li></ul></ul></ul>
  4. 4. Heat Production <ul><li>Exergonic reactions: </li></ul><ul><ul><li>Oxidation and ATP use. </li></ul></ul><ul><li>Most heat generated by brain, heart, liver and glands at rest. </li></ul><ul><li>Skeletal muscles 20-30% at rest. Can increase 30-40 times during exercise. </li></ul>
  5. 5. Thermoregulatory Center <ul><li>Hypothalamus: </li></ul><ul><ul><li>Preoptic area neurons: hypothalamic thermostat: </li></ul></ul><ul><ul><ul><li>Heat-losing center </li></ul></ul></ul><ul><ul><ul><li>Heat-promoting center </li></ul></ul></ul><ul><li>Monitors temperature of blood and receives signals from peripheral thermoreceptors. </li></ul><ul><li>Negative feedback loops </li></ul>
  6. 6. Thermoregulatory Center <ul><li>Heat-losing center: </li></ul><ul><li>Activates heat losing mechanisms: </li></ul><ul><ul><li>Dilation of dermal arterioles: increase blood flow to skin. </li></ul></ul><ul><ul><li>Sweating. </li></ul></ul><ul><ul><li>Increased respiration through mouth. </li></ul></ul><ul><ul><li>Behavioral: remove clothing. </li></ul></ul><ul><li>Inhibits heat-promoting center. </li></ul>
  7. 7. Thermoregulatory Center <ul><li>Heat-promoting center: </li></ul><ul><li>Activates heat generating mechanisms: </li></ul><ul><ul><li>SNS: </li></ul></ul><ul><ul><ul><li>Vasoconstriction of dermal arterioles: decrease blood flow to skin </li></ul></ul></ul><ul><ul><ul><li>Stimulates arrector pili muscles: hair stands on end </li></ul></ul></ul><ul><ul><ul><li>Shivering thermogenesis: spinal reflex of alternating contractions in antagonistic muscles </li></ul></ul></ul><ul><ul><li>Nonshivering thermogenesis: </li></ul></ul><ul><ul><ul><li>Long-term mechanism stimulating thyroid hormone release T 3 and T 4 . </li></ul></ul></ul><ul><ul><li>Inhibits heat-loss center. </li></ul></ul>
  8. 8. Thermoregulatory Center <ul><li>Hypothalamus: </li></ul><ul><li>Peripheral thermoreceptors: </li></ul><ul><ul><li>Temperature of skin. </li></ul></ul><ul><li>Central thermoreceptors: </li></ul><ul><ul><li>Temperature of core. </li></ul></ul><ul><ul><li>Most important located in hypothalamus. </li></ul></ul>
  9. 9. Mechanisms of Heat Transfer <ul><li>Radiation: </li></ul><ul><ul><li>Infrared radiation. </li></ul></ul><ul><li>Conduction: </li></ul><ul><ul><li>Direct transfer of energy through physical contact. </li></ul></ul><ul><li>Convection: </li></ul><ul><ul><li>Heat loss to air around the human body. </li></ul></ul><ul><li>Evaporation: </li></ul><ul><ul><li>Energy change in water molecule from liquid to vapor. </li></ul></ul>
  10. 10. Heat Exhaustion <ul><li>Acute heat injury due to dehydration. </li></ul><ul><li>Heat-loss center stimulated. </li></ul><ul><ul><li>Sweat production increases. </li></ul></ul><ul><ul><li>Decrease in BP because heat loss center stimulates peripheral vasodilation. </li></ul></ul><ul><ul><li>Blood flow to brain decreases. </li></ul></ul><ul><li>Compensatory mechanisms: </li></ul><ul><ul><li>SNS </li></ul></ul><ul><ul><li>Aldosterone </li></ul></ul><ul><ul><li>ADH </li></ul></ul>
  11. 11. Heat Exhaustion <ul><li>Symptoms: </li></ul><ul><ul><li>Headache </li></ul></ul><ul><ul><li>Nausea </li></ul></ul><ul><ul><li>Actively sweating </li></ul></ul><ul><ul><li>Skin cool and pale </li></ul></ul><ul><ul><li>Fainting </li></ul></ul><ul><li>Treatment: </li></ul><ul><ul><li>Increase fluids </li></ul></ul><ul><ul><li>Shade or AC room </li></ul></ul><ul><ul><li>Cold wet towels </li></ul></ul><ul><li>Can progress to heat stroke. </li></ul>
  12. 12. Heat Stroke <ul><li>Core rectal temperature approaches 41 o C </li></ul><ul><li>2 types: </li></ul><ul><li>Individuals with compromised homeostatic mechanisms: </li></ul><ul><ul><li>Young children </li></ul></ul><ul><ul><li>Elderly </li></ul></ul><ul><li>Exertional: </li></ul><ul><ul><li>Healthy individual under strenuous exercise </li></ul></ul>
  13. 13. Heat Stroke <ul><li>Renal and splanchnic vasoconstriction. </li></ul><ul><li>Peripheral blood flow decreases. </li></ul><ul><li>Impaired thermoregulation. </li></ul><ul><li>CNS dysfunction: </li></ul><ul><ul><li>Cerebral edema and increased intracranial pressure. </li></ul></ul><ul><li>Tissue damage due to uncoupling during oxidative phosphorylation. </li></ul><ul><li>Proteins denature. </li></ul>
  14. 14. Heat Stroke Complications <ul><li>Rhabomyolysis </li></ul><ul><li>Multiple organ failure: </li></ul><ul><ul><li>Cardiac </li></ul></ul><ul><ul><li>Hepatic </li></ul></ul><ul><ul><li>Renal </li></ul></ul><ul><li>DIC: fibrinolysis </li></ul><ul><li>CNS hallucinations, coma </li></ul><ul><li>Anhydrosis more common in classic than exertional heat stroke. </li></ul>
  15. 15. Heat Stroke Treatment <ul><li>Drop core temperature by 0.2 o C/min </li></ul><ul><li>Institute evaporative cooling methods: </li></ul><ul><ul><li>Remove clothing and spray body with water while cooling with fans. </li></ul></ul><ul><li>Correct water deficit </li></ul><ul><li>Oxygen </li></ul><ul><li>Give chlorpromazine: </li></ul><ul><ul><li>Depresses shivering during treatment </li></ul></ul>
  16. 16. Exercise <ul><li>Maximum exercise, heat production can be 10-20 times resting. </li></ul><ul><li>Highest temperatures occur in the exercising muscles. </li></ul><ul><li>Body temperature increases during exercise and levels off a few degrees above normal (except at extreme temperatures). </li></ul><ul><li>Regulated response with heat loss = heat production at a stabilized core temperature. </li></ul>
  17. 17. Exercise Acclimatization <ul><li>Exercise in the heat for two weeks at a safe intensity. </li></ul><ul><li>Plasma volume increases 12%. </li></ul><ul><li>Sweating occurs at lower temperature. </li></ul><ul><li>Sweat rate increases as much as 3 times. </li></ul><ul><li>Sweat osmolality decreases. </li></ul>
  18. 18. Hypothermia <ul><li>Core temperature below 95 o F. </li></ul><ul><li>Gradual loss of mental and physical activity. </li></ul><ul><li>Changes in motor coordination. </li></ul><ul><li>Shivering. </li></ul><ul><li>Slurred speech. </li></ul><ul><li>Abnormally slow rate of breathing. </li></ul><ul><li>Cold, pale skin. </li></ul><ul><li>Fatigue, lethargy. </li></ul>
  19. 19. Hypothermia <ul><li>If core temperature remains above 90 o F, recovery is good. </li></ul><ul><li>If core temperature falls below 80 o F, prognosis poor. </li></ul><ul><li>Treatment: </li></ul><ul><ul><li>Move person out of cold. </li></ul></ul><ul><ul><li>Insulate the person’s body. </li></ul></ul><ul><ul><li>Warm beverages. </li></ul></ul><ul><ul><li>Give warm IV fluids, slowly otherwise vasodilation occurs, bringing too large volume of chilled blood; cardiac arrhythmias . </li></ul></ul><ul><li>Frostbite: </li></ul><ul><ul><li>Vasoconstriction to cold, causes irreparable tissue damage. </li></ul></ul><ul><ul><ul><li>Cells decrease ATP production, hypoxia. </li></ul></ul></ul><ul><ul><li>Do not rub tissue. </li></ul></ul>

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