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 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

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

15. 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

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