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Thermoregulation. Homeostasis. Homeostasis. organ systems are interdependent share same environment c omposition effects all inhabitants internal environment must be kept stable maintaining stable internal environments-homeostasis dynamic equilibrium. Homeostasis.
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Thermoregulation Homeostasis
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
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
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
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
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
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
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
Mechanisms of Heat Transfer • Radiation • Conduction • Convection • Evaporation
Evaporation • water changes from liquid to vapor
ThermoregulationHomeostasis • Control Center • preoptic area of hypothalamus • Receptors • in skin • Effectors • eccrine sweat glands & blood vessels
skin receptors detect increase in temperaturemessage sent to preoptic nucleus heat loss center (also in hypothalamus)stimulated sets off series of events heat loss inhibition of vasomotor centerperipheral vasodilationwarm blood flows to skin’s surface as skin temperatures rise, radiation & convection loses increase sweatglands stimulated increase output evaporative loss increases respiratory centers stimulateddepth of respiration increases Mechanisms for HeatLoss
Mechanisms for Heat Gain • skin receptors notice temperature is droppingpreoptic 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 stimulatedhair stands on endtraps air near the skin
Heat Gain • if vasoconstriction cannot restore or maintain core temperatureshivering thermogenesis begins • gradual increase in muscle tone • increases energy consumption by skeletal muscle throughout body • increases work load of muscles & elevates O2 & energy consumptionproduces heat which warms deep vessels to which blood has been shunted by sympathetic vasomotor center • can increase rate of heat generation by 400%
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 ANSepinephrine released increases rate of glycogenolysis (break down of glycogen) in liver & skeletal musclemetabolic 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