Thermal Physiology C H A P T E R. PowerPoint Lecture Slides prepared by Stephen Gehnrich, Salisbury University

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1 C H A P T E R 13 Thermal Physiology PowerPoint Lecture Slides prepared by Stephen Gehnrich, Salisbury University

2 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

3 Acclimation of metabolic rate to temperature in a poikilotherm (chronic response) (5 weeks) (5 weeks)

4 Compensation for temperature changes (chronic response) Temperature acclimation Partial compensation Full compensation

biochemical reaction, biophysical reactions) 2.

5 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.

6 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.

7 The enzyme of Antarctic fish is very sensitive to temperature changes Eurythermal species Stenothermal species

8 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.

by different composition of membrane phospholipid

9 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)

10 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

11 Homeoviscous Adaptation Figure 13.12

12 Thermal Adaptations Ectotherms remodel tissues in response to longterm 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

13 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

14 Heat Shock Response Figure 13.15

15 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

16 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

17 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

18 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

19 Antifreeze Proteins Figure 13.16

20 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

21 Thermal Strategies Figure 13.6

22 Thermal classification of real v.s. ideal animals Poikilothermic animals Homeothermic animals Ectothermic animals Endothermic animals Heterothermic animals

Heterothermic animals: Regional heterotherm maintain regions of their body above ambient temperature (tuna, flying insects) Temporal heterotherm whose temperatures vary widely over

23 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.

Some pelagic fishes, tunas, sharks, bill fishes, temperatures within

24 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. Red muscles Counter-current exchange (rete mirabile) vein artery

25 Countercurrent Heat Exchanger Figure 13.22

26 Bluefin tunas, which reach body weights of 700kg, maintain fairly constant red-muscle temperatures over a wide range of water temperature. (endothermic thermo-regulator)

27 Poikilotherms often exert behavioral control over their body temperatures (behavioral thermoregulation)

The thermoregulation of endotherms Homeothermic endotherms Mammals: 37~38 Birds: 40 The basal metabolic rates of Endotherms/ectotherms = 7~20 (thermogenesis) (Sweating Panting) During

28 The thermoregulation of endotherms Homeothermic endotherms Mammals: 37~38 Birds: 40 The basal metabolic rates of Endotherms/ectotherms = 7~20 (thermogenesis) (Sweating Panting) During thermal neutral zone, animal regulate body temp. through adusting the rate of heat loss: Vasomotor response Postural changes Insulation adustments Lower critical termp. Upper critical termp.

29 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

30 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

31 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

32 Brown Adipose Tissue (BAT) Figure 13.18

heat Nonshivering thermogenesis: modified superior rectus eye muscles

33 Thermogenesis in brown fat is characterized by the appearance in the inner mitochondria membrane of an uncoupling protein (thermogenin). heat Nonshivering thermogenesis: modified superior rectus eye muscles in billfishes are specialized for heat production rather than force generation

34 Regulation of Body Temperature Coordination of multiple physiological systems Internal Thermostat Mammals Information from central and peripheral thermal sensors is integrated in the hypothalamus Hypothalamus sends signals to the body to alter rates of heat production and dissipation Birds Thermostat is located in the spinal cord

35 Regulation of Body Temperature Figure 13.19

36 Vasomotor Response Figure 13.21

37 Countercurrent Exchange of Heat Transfer thermal energy from warm arterial blood to cooler venous blood Heat is retained Important in regionally heterothermic fish and birds

38 Sweating Used primarily by large animals Low surface area to volume ratios Sweat reduces body temperature by evaporative cooling NaCl in sweat raises heat of vaporization Greater heat loss than evaporation of pure water Sweating is controlled by the hypothalamus Sympathetic innervation of sweat glands To minimize ionic and osmotic problems, the amount of NaCl in sweat decreases during long periods of heat exposure

39 Sheep and some other mammals have a carotid rete mirabile for counter current cooling of carotid blood. The brain temperature may be 2~3 lower than core body temperature

40 Thermoregulation and specialized metabolic states Many animals have evolved various forms of dormancy to lower their metabolism and thus the food requirement. Dormancy states include: sleep, daily torpor, hibernation, winter sleep, estivation (all states in which an animal allows its body temperature to approximate ambient temperature within a specific range of ambient temperature.) Daily torpor: part of each day Hibernation: days to months during winter Winter sleep: similar to hibernation, but their body temp. drop only a few degrees Estivation: days to months during summer (summer sleep)

41 Relaxed Endothermy Figure 13.25

1. Two main types. 2. Both strategies have costs and benefits 3. Do not use warm-blooded and coldblooded to describe strategies. 1.

1. Two main types. 2. Both strategies have costs and benefits 3. Do not use warm-blooded and coldblooded to describe strategies. 1. Thermal Strategies: Chapter 10 1. Two main types A. Tolerance B. Regulation 2. Both strategies have costs and benefits 3. Do not use warm-blooded and coldblooded to describe strategies. Terminology 1.