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 Positive 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

Negative Feedback

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

Thermoregulation Homeostasis Control Center preoptic area of hypothalamus Receptors in skin Effectors eccrine sweat glands & blood vessels

Mechanisms for Heat Loss 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 sweat glands stimulated increase output evaporative loss increases respiratory centers stimulateddepth of respiration increases

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

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%

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