1. Temperature Regulation
Gen. Physiology
Biology 346
Misericordia University

2. Thermal Environment
Conduction –transfer of heat between solids directly in contact
Convection –transfer of heat by movement of liquid or gas
Radiation –spectral emission of heat in the form of light (IR)
Evaporation / Condensation – transference of heat through the loss of water

3. Conduction Convection Radiation Dependent on:
Surface area contact
Temperature gradient
Thermal properties of materials
Consists of a conductive heat exchange between an object and a gas or liquid (with a undisturbed boundary layer and a disturbed layer)
Dependent on:
Temperature gradient
Surface area contact
Fluid’s viscosity, heat capacity, and thermal expansion
Thickness of boundary layer
Radiation
Net exchange dependent on:
Surface temperature of object
Temperature of transference media

4. Evaporation / Condensation
Dependent on:
Difference of water vapor density between surface and surrounding media
Thickness of boundary layer
Temperature gradient

5. Thermodynamic Principles
ENVIRONMENT
Radiation
Conduction
Convection
Evaporation
ENVIRONMENT
Radiation
Conduction
Convection
HEAT GAIN
ANIMAL
HEAT LOSS
METABOLISM
Maintenance
Exercise
Growth
Lactation
Feeding
METABOLISM
Milk Removal
Fecal Removal
Urinary Removal

6. Heat Gain and Loss from Internal Environment
15%

7. In general, reaction rates increase with increasing temperature.
Q10 is the rate of a reaction at a given temperature compared to its rate 10o C cooler. (compares reaction rates of same reaction at different temperatures; most biological reactions increase 2-3x for each 10oC rise in temperature)

8. Effect of Temperature on Metabolism
Reaction rate reaches a maximum at an optimal temperature then begins to decline (due to denaturation)
Active metabolism of animals seems to be restricted to narrow range (-2oC to 50oC)
Temp., oC
Percent max activity
Optimal 20 40 80 60

9. Molecular Thermo-adaptations
Degree of saturation of fatty acids in cell membranes
Saturated membranes decrease fluidity of membrane; allowing them to work at higher temp.
Polyunsaturated membranes increase fluidity; allowing them to operate at low temp.
Some organisms can change the degree of saturation as an acclimating change (trout)
Enzymes may also show adaptations as well Ex. LDH (lactate dehydrogenase) changes in flexibility

10. Endotherms and Ectotherms
Endotherms- maintain elevated body temperature (Tb) by endogenous heat production
High VO2 (rate of oxygen consumption), high heat production, low thermal conductivity (good insulation)
high metabolic cost, 5x metabolism of ectotherms
Allows organism to exist actively at extremes of temperature
Ectotherms- adjust Tb by means other than heat production and heat loss
Low VO2, low heat production, Tb may vary with environment

11. Exotherms vs. Endotherms

12. Ectotherm Adaptations
Ectotherm Tb may follow the environment or be regulated by external changes
Microenvironment selection
Basking/ movement
Shading
Vasoconstriction/dilation
Body position, shape, color (special structures: frills, open mouth, etc.)

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15. Endotherm Adaptations
Endotherms primarily use internal homeostatic reflexes to maintain Tb
Cold Stress
Elevate heat production: muscular activity (movement, shivering, digesting), brown fat, behavior
Minimize heat loss: large body mass, behavior (position, nest), insulation, piloerection, vasoconstriction, counter current exchangers

16. Counter current exchangers

17. Chemical Thermogenesis
Brown adipose cells have high amounts of triglycerides and mitochondria with thermogenin embedded cristae
H+ flow is uncoupled from ATP synthesis and generates large amounts of heat
Found in newborn mammals, most small mammals and hibernators

18. Endotherm Adaptations
Heat Stress
Decrease heat production: lower activity levels
Behavior (posture, shade, etc.)
Maximize heat loss:
low body mass,
change insulation, color
vasodilation to skin,
vasodilation to specific cooling areas,
counter current exchangers
increase evaporation: sweating, panting

19. Specific organ cooling: rete

20. Mammalian Thermal Reflex

21. Human Responses

22. Thermal neutral zone
Range of ambient temperature (Ta) in which endotherm does not need to alter VO2 to maintain constant Tb.
Upper critical temperature (UCT)-Ta above which energy-requiring heat loss mechanisms are used- sweating, panting.
Lower critical temperature (LCT)- energy-requiring heat production mechanisms are used- shivering, non-shivering thermiogenesis.
UCT

23. anphys-fig jpg

24. Special Adaptations to Extremes
Wood Frog
(Rana sylvatica)
Special Adaptations to Extremes
Antifreezes (freeze tolerance and intolerance)
Hyperthermia and Hypothermia (Super cooling)
Dormancy: torpor, hibernation, estivation
Heat shock response
Fever
Gray tree frog (Hyla versicolor)

25. Melting point depression –Freeze tolerance
Glycerol or sugars used to lower freezing point of body fluids (ECF and blood)
Massive accumulation in ICF, preventing freezing of cytoplasm, but allowing freezing of ECF.
Some species produce nucleating agents to control growth of ice in ECF (small rather than large crystals)
As ice forms changes osmolarity of ECF, sugars in ICF balance this rise and prevent sudden dehydration of cell. Sugars are also used as individual warms as nutrition source before circulation resumes.

26. Freeze-tolerant animals
Wood frogs live in Canada and northern US.
30-50% of body fluids can freeze. The animals thaw out in the spring.
Other freeze-tolerant animals:
juvenile painted turtles (Chrysemys picta)
gray tree frog (Hyla versicolor)
garter snake (Thamnophis sirtalis)
Eastern box turtle

27. Antarctic Icefish- freeze intolerance
Antifreeze proteins in ICF and ECF
Antarctic icefish such as Trematomus, the so-called rock cod, live in water at temperatures around -1.8o C (28.7o F).
These fish cannot survive their body fluids freezing.
They produce unique antifreeze proteins that increase blood osmolarity and reduce the blood freezing point. Also combine with ice crystals to prevent their growth.
These fish die at an upper lethal temperature of 6o C (42.8o F), the lowest upper lethal temperature of any fish.
Trematomus bernacchii
McMurdo Sound, Antarctica

28. Allowed Hyperthermia & Hypothermia
Some animals may allow body core temperature to rise or lower well beyond set point for extended period of time
Hypothermia (Super Cooling) -Prevention of nucleation site for ice crystal formation allows the body core temperature to drop. Dangerous as contact with external ice may induce rapid freezing. –some turtles
Hyperthermia –body core temperature is allowed to rise, usually to prevent excessive loss of water through evaporation -camels

29. Hibernation
Prolonged dormant state with body core temperature approaching 0oC
Must store large amounts of unsaturated fats
Hypothalamus functions to prevent body from freezing by generating uncoupled metabolism in brown fat, white fat, and muscle. Animals go through periodic warming periods.
Only marmot size animals can be true hibernators; since large body masses could not cool down and reheat in one season
Bears (not a true hibernator) since core temp drops by only 2-5oC, but do go through many of the same processes

30. Hibernation

31. Estivation Torpor A daily hibernation found in some animals
At night body temp can drop to temperatures as low as 15-20oC
Allows animal to conserve energy
May lead to an extended life span
Estivation
Dormancy (similar to torpor) period induced during warm temperature because of other negative conditions (such as low oxygen levels in water, dry conditions, etc.)
Allows animal to conserve energy

32. Heat Shock Response
Heat Shock Proteins –help to fold denaturing proteins back to their normal conformation
Generated in many stressful situations
Found in most species
Antartic fish seem to have none

33. Fever Resetting of body core set point to fight infection
Aspirin works by interfering in prostaglandin synthesis in hypothalamus