Temperature Regulation Gen. Physiology Biology 346 Misericordia University
Temperature Regulation Gen. Physiology Biology 346 Misericordia University 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 Conduction
Dependent on: Surface area contact Temperature gradient Thermal properties of materials Radiation Net exchange dependent on: Surface temperature of object
Temperature of transference media Convection 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 Fluids viscosity, heat capacity, and thermal expansion Thickness of boundary layer Evaporation / Condensation Dependent on: Difference of water vapor density between surface and surrounding media
Thickness of boundary layer Temperature gradient Thermodynamic Principles ENVIRONMENT Radiation Conduction Convection Evaporation ENVIRONMENT Radiation
HEAT LOSS METABOLISM Milk Removal Fecal Removal Urinary Removal Heat Gain and Loss from Internal Environment 15%
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)
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) Percent max activity
Effect of Temperature on Metabolism Optimal 0 20 40 Temp., oC
60 80 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 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
Exotherms vs. Endotherms 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.) Endotherm Adaptations Endotherms primarily use internal homeostatic reflexes to maintain T b 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 Counter current exchangers 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 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 Specific organ cooling: rete
Mammalian Thermal Reflex Human Responses 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 usedsweating, panting. Lower critical temperature (LCT)- energy-requiring heat production mechanisms are usedshivering, non-shivering thermiogenesis. UCT
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) 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. 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 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 Trematomus bernacchii that increase blood osmolarity and McMurdo Sound, Antarctica 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. 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 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 Hibernation 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
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 Fever Resetting of body core set point to fight infection
Aspirin works by interfering in prostaglandin synthesis in hypothalamus
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