Thermoregulation

1. Thermoregulation Homeostasis

2. Homeostasis • organ systems are interdependent • share same environment • composition effects all inhabitants • internal environment must be kept stable • maintaining stable internal environments-homeostasis • dynamic equilibrium

3. Homeostasis • varies around a Set Point • average value for a variable • specific for each individual • determined by genetics • normal ranges for a species • temperature 36.7 – 37.2

4. Parts of Homeostatic Regulation • Receptor • sensitive to environmental change or stimuli • Control or Integration Center • receives & processes information supplied by receptor • determines set point • Effector • cell or organ which responds to commands of control center

6. HOMEOSTATIC REGULATION • Autoregulation • cells, tissues, organs adjust automatically to environmental changes • Extrinsic Regulation • Nervous System • Fast • Short lasting • Crisis management • Endocrine System • Longer to react • Longer lasting

7. FEEDBACK LOOPS • Negative Feedback • output of system shuts off or reduces intensity of initiating stimulus • most often seen in the body • Positive Feedback • initial stimulus produces a response that exaggerates or enhances its effect • blood clotting & child birth

8. Negative Feedback

10. Temperature Extremes • Humans are subjected to vast changes in environmental temperatures • Enzymes operate over very narrow range of temperatures • Failure to control body temperature can result in physiological changes & damage • body has several mechanisms to maintain body temperature • Thermoregulation

11. Temperature • Core temperature • most important body temperature • temperature of organs in major cavities • rectal temperature gives best estimation • Shell temperature • temperature closer to surface • skin & oral temperatures

12. Mechanisms of Heat Transfer • Radiation • Conduction • Convection • Evaporation

13. Evaporation • water changes from liquid to vapor

14. ThermoregulationHomeostasis • Control Center • preoptic area of hypothalamus • Receptors • in skin • Effectors • eccrine sweat glands & blood vessels

15. skin receptors detect increase in temperaturemessage sent to preoptic nucleus heat loss center (also in hypothalamus)stimulated sets off series of events heat loss inhibition of vasomotor centerperipheral vasodilationwarm blood flows to skin’s surface as skin temperatures rise, radiation & convection loses increase sweatglands stimulated increase output evaporative loss increases respiratory centers stimulateddepth of respiration increases Mechanisms for HeatLoss

16. Mechanisms for Heat Gain • skin receptors notice temperature is droppingpreoptic nucleus notificed • heat loss center inhibited • heat gain center activated • sympathetic vasomotor center decreases blood flow to dermis of skin • vasoconstriction reduces heat loss by radiation, convection & conduction • blood returning from limbs is shunted into deep veins • Piloerector muscles are stimulatedhair stands on endtraps air near the skin

17. Heat Gain • if vasoconstriction cannot restore or maintain core temperatureshivering thermogenesis begins • gradual increase in muscle tone • increases energy consumption by skeletal muscle throughout body • increases work load of muscles & elevates O2 & energy consumptionproduces heat which warms deep vessels to which blood has been shunted by sympathetic vasomotor center • can increase rate of heat generation by 400%

18. Heat Gain • Non shivering thermogenesis • long term mechanism for heat production • sympathetic nervous system & thyroid hormone produce an increase in metabolism • Heat gain center stimulates adrenal medulla via sympathetic ANSepinephrine released increases rate of glycogenolysis (break down of glycogen) in liver & skeletal musclemetabolic rate increases • preoptic nucleus regulates production of TRH-thyrotropin releasing hormone by the hypothalamus • TRH increases production of thyroxin by thyroid gland • Thyroxin is a key hormone in control of metabolism