Body Temperature and Its Regulation Lecture 7.pdf

Pharm D

1. BODYTEMPERATUREANDITS
REGULATION
Dr. Najam-us-Sahar
Senior Lecturer

2. REGULATIONOFBODYTEMPERATURE
•Bodytemperaturereflectsthebalancebetweenheatproductionand
heatloss
•Atrest,theliver,heart, brain,kidneys,andendocrine organs
generatemostheat
•Duringexercise,heatproductionfromskeletalmuscles increases
dramatically

3. Normalbodytemperature=37C5C(98.6F)
Optimalenzymeactivityoccursatthis temperature
Increasedtemperaturedenaturesproteinsand depressesneurons
REGULATIONOFBODYTEMPERATURE

4. •Basalmetabolism
•Muscularactivity
(shivering)
•Thyroxineand
epinephrine
(stimulatingeffects
onmetabolicrate)
•Temperatureeffect
oncells
•Radiation
•Conduction/
convection
•Evaporation
Heatproduction Heatloss

5. COREANDSHELLTEMPERATURE
Organsinthecorehavethehighesttemperature Bloodisthemajoragent
ofheatexchangebetweenthecoreandtheshell
Coretemperatureisregulated
Coretemperatureremainsrelativelyconstant, whileshelltemperature
fluctuates substantially(20C–40C)

6. MECHANISMSOFHEATEXCHANGE
Fourmechanisms
1.Radiationisthelossofheatintheformof infraredrays
2.Conductionisthetransferofheatbydirect contact
3.Convectionisthetransferofheattothe surroundingair
4.Evaporationistheheatlossduetothe evaporationof
waterfrombodysurfaces

7. MECHANISMSOFHEATEXCHANGE
•Insensibleheatlossaccompaniesinsensible waterlossfromlungs,
oralmucosa,andskin
•Evaporativeheatlossbecomessensible (active)whenbody
temperaturerisesand sweatingincreaseswatervaporization

8. ROLEOFTHEHYPOTHALAMUS
Hypothalamuscontainsthetwo thermoregulatory
centers
AnteriorHypothalamus:activatesthe mechanismthatpromote
Heat-loss.
PosteriorHypothalamus:activatesthe mechanismthatincreaseHeat-
productionand promoteheatgain.

9. ROLEOFTHEHYPOTHALAMUS(THERMOSTAT)
Thehypothalamusreceivesafferentinput from
Peripheralthermoreceptorsintheskin
Centralthermoreceptors(someinthe hypothalamus)
Initiatesappropriateheat-lossandheat-promoting
activities

12. HEAT-PROMOTINGMECHANISMS
•Constrictionofcutaneousbloodvessels
•Shivering
•Increasedmetabolicratevia epinephrineand
norepinephrine
•Enhancedthyroxinerelease

13. HEAT-PROMOTINGMECHANISMS
•Voluntarymeasuresinclude
Puttingonmoreclothing
Drinkinghotfluids
Changingpostureorincreasingphysical activity

14. HEAT-LOSSMECHANISMS
•Dilationofcutaneousbloodvessels
•Enhancedsweating
•Voluntarymeasuresinclude
-Reducingactivityandseekingacoolerenvironment
-Wearinglight-coloredandloose-fittingclothing

15. Sweatglandsactivated:
secreteperspiration,
whichisvaporizedby
bodyheat,helpingto
coolthebody
Skinbloodvesselsdilate:
capillariesbecomeflushed
withwarmblood;heatradiates
fromskinsurface
Bodytemperature
decreases:blood
temperaturedeclines
andhypothalamus
heat-losscenter
“shutsoff”
Activatesheat-
losscenterin
hypothalamus
Stimulus
Increasedbody
temperature;
bloodwarmer
thanhypothalamic
setpoint

16. Stimulus
Decreased
bodytempera-
ture;blood
coolerthan
hypothalamic
setpoint
Activatesheat-
promotingcenter
inhypothalamus
Bodytemperature
increases:blood
temperaturerises
andhypothalamus
heat-promoting
center“shutsoff”
Skeletalmuscles
activatedwhenmore
heatmustbegenerated;
shiveringbegins
Skinbloodvesselsconstrict:
bloodisdivertedfromskin
capillariesandwithdrawnto
deepertissues;minimizes
overallheatlossfromskin
surface