C H A P T E R 13 Thermal Physiology PowerPoint® Lecture Slides prepared by Stephen Gehnrich, Salisbury University Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Thermal Tolerance of Animals Eurytherm Can tolerate a wide range of ambient temperatures Stenotherm Can tolerate only a narrow range of ambient temperatures Eurytherms can occupy a greater number of thermal niches than stenotherms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Acclimation of metabolic rate to temperature in a poikilotherm (chronic response) (5 weeks) (5 weeks) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Compensation for temperature changes (chronic response) “Temperature acclimation” Partial compensation Full compensation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Temperature is important for animal tissues for two reasons: 1. Temperature affects the rates of tissue processes (metabolic rates, biochemical reaction, biophysical reactions) 2. Temperature affects the molecular conformations, and therefore, the functional states of molecules. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Different species have evolved different molecular form of enzymes. All six species have about the same enzyme-substrate affinity when they are at their respective body temperature. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The enzyme of Antarctic fish is very sensitive to temperature changes Eurythermal species Stenothermal species Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The functional properties of lipids depend on the prevailing temperature and chemical composition of the molecules. Membrane fluidity is a measure of how readily the phospholipid in a membrane move. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Membrane fluidity is kept relatively constant at the respective ordinary body temperature of the species by different composition of membrane phospholipid (saturation of the phospholipid). (Highly unsaturated lipids) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Homeoviscous Adaptation Homeoviscous adaptation Maintain membrane fluidity at different temperatures by changing membrane lipids Mechanisms of homeoviscous adaptation Fatty acid chain length Shorter chains increase fluidity Saturation More double bonds increase fluidity Phospholipid classes Phosphatidylcholine (PC): decrease fluidity Phosphatidylethanolamine (PE): increase fluidity Cholesterol content Prevents solidifying when the membrane is cooled Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Homeoviscous Adaptation Figure 13.12 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Thermal Adaptations Ectotherms remodel tissues in response to long- term changes in temperature Quantitative strategy More metabolic “machinery” For example, increase the number of muscle mitochondria in low temperature Qualitative strategy Alter the type of metabolic “machinery” For example, different myosin isoforms in winter and summer Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Heat Shock Response Proteins denature at high temperatures Accumulation of denatured proteins can kill the cell Heat shock proteins (Hsp’s) Molecular chaperones that catalyze protein folding and help refold denatured proteins Heat shock response Increase in the levels of Hsp’s in response to extreme temperatures Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Heat Shock Response Figure 13.15 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Strategies for Surviving Freezing Temperatures Freeze-tolerance Animals can allow their tissues to freeze Freeze-avoidance Animals use behavioral and physiological mechanisms to prevent ice crystal formation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Strategies for Surviving Freezing Temperatures Supercooling In the absence of a nucleator, water can remain liquid below 0°C (lowest is –40°C) Ice crystal formation needs a trigger Either a cluster of water molecules or a macromolecule that acts as a nucleator Deleterious effects of ice crystal formation Points and edges can pierce membranes Crystal growth removes surrounding water Osmolarity increases Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Freeze-Tolerance Two mechanisms of freeze-tolerance Produce nucleators outside of the cell Control the location and kinetics of ice crystal growth Extracellular fluid freezes, but intracellular fluid remains liquid Produce intracellular solutes to counter the movement of water Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Freeze-Avoidance Solutes depress the freezing point of a liquid (colligative property of water) As osmolarity increases, freezing point decreases Antifreeze macromolecules Proteins or glycoproteins that depress the freezing point by noncolligative actions Disrupt ice crystal formation by binding to small ice crystal and preventing growth Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Antifreeze Proteins Figure 13.16 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Thermal Strategies Relative stability of body temperature Poikilotherm Variable body temperature Homeotherm Stable body temperature Source of thermal energy Ectotherm Environment determines body temperature Endotherm Animal generates internal heat to maintain body temperature Most animals best described by a combination of terms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Thermal Strategies Figure 13.6 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Thermal classification of real v.s. ideal animals Poikilothermic animals Homeothermic animals Ectothermic animals Endothermic animals Heterothermic animals Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Heterothermic animals: Regional heterotherm — maintain regions of their body above ambient temperature (tuna, flying insects) Temporal heterotherm — whose temperatures vary widely over time (torpor , hibernation) Winter moth uses preflight thermogenesis to remain active. Voluntary shivering of the thoracic flight muscles caused a steep increase in thoracic temperature. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Warm bodied fishes The body temperature of 99% of all species of fish closely approximate water temperature. Some pelagic fishes, tunas, sharks, bill fishes, temperatures within certain body regions exceed water temperature. Counter-current exchange Red muscles (rete mirabile) 30 25 20 15 10 vein artery Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Countercurrent Heat Exchanger Figure 13.22 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bluefin tunas, which reach body weights of 700kg, maintain fairly constant red-muscle temperatures over a wide range of water temperature. (endothermic thermo-regulator) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Poikilotherms often exert behavioral control over their body temperatures (behavioral thermoregulation) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The thermoregulation of endotherms Homeothermic endotherms Mammals: 37~38 ℃ Birds: 40 ℃ The basal metabolic rates of Endotherms/ectotherms = 7~20 During thermal neutral zone, animal regulate body temp. through adusting the rate of heat loss: (thermogenesis) (Sweating Panting) Vasomotor response Postural changes Insulation adustments Lower critical termp. Upper critical termp. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Maintaining a Constant Body Temperature Endothermy intertwined with high metabolic rate High metabolic rate causes ↑ heat production Thermogenesis Advantages of high body temperature ↑ growth, development, digestion, biosynthesis Endothermy requires ability to regulate Thermogenesis Heat exchange with environment Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Shivering Thermogenesis Unique to birds and mammals Uncoordinated myofiber contraction that results in no gross muscle contraction Works for short periods of time Muscles are rapidly depleted of nutrients and become exhausted Prevents the animal from using locomotory muscle for foraging or predator avoidance Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Brown Adipose Tissue (BAT) Used for nonshivering thermogenesis Important in thermogenesis for small mammals and newborns that live in cold environments Located near the back and shoulder region Differs from white adipocytes Higher levels of mitochondria Produces the protein thermogenin Thermogenin uncouples the mitochondrial electron transport system and proton pumping from ATP synthesis High rate of fatty acid oxidation Energy is released as heat Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Brown