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Energetics 2 Really Temperature 4

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Energetics 2 Really Temperature 4

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    1. 1 Energetics (2) (Really Temperature 4) Endothermy Regional heterothermy Facultative ectothermy (NOTE: this is actually correct – endotherms become more like ectotherm facultatively = under certain conditions) Torpor Hibernation Regulating Body temperature Generating heat Shivering thermogenesis Nonshivering thermogenesis Measuring energy consumption

    2. 2 Regional Heterothermy Different regions of body = different temperatures Countercurrent heat exchangers Bird and Mammal legs Flippers Ungulate antlers Beaver tails Ears of arctic hares Tuna swimming muscles!

    3. 3 Counter-current heat exchange

    4. 4 Bird legs have countercurrent exchangers

    5. 5 Why don’t their feet freeze?

    6. 6 Why don’t their feet freeze?

    7. 7 Rete mirabile Anatomical arrangement of circulatory system Consists of bundles of arterioles and venules In close appostion (stuck together) Running in opposite directions Countercurrent exchanger of both gas and heat

    8. 8 Regional endothermy in Tunas

    9. 9 Regional heterothermy In bird example, arteries into legs carry warmer blood, veins returning from feet carry cooler blood In tuna example, arterioles into muscle capillaries carry cool blood, venules carry warm blood In both cases countercurrent exchange is used to maintain distinct temperature zones in body

    10. 10 Costs of endothermy When is it most expensive to be a homeothermic endotherm? When it’s REALLY COLD When you’re SMALL Rate of heat loss is proportional to surface area Rate of heat production is proportional to VOLUME Heat Loss/Heat production ~ SA/volume

    11. 11 Surface area to volume ratio Corrections in BOLD

    12. 12 Hibernation and Torpor Both are ways of turning down the thermostat to save energy Can be distinguished by the length of bouts: Hibernation tends to be seasonal Deep hibernators are small mammals Bears undergo shallow hibernation Too much energy to warm up their big mass Torpor tends to be daily (or nightly) Tend to be very small birds and mammals These animals can re-warm fairly quickly

    13. 13 Torpor

    14. 14 Torpor in small mammals: bats

    15. 15 Torpor in small mammals: bats

    16. 16

    17. 17 Hibernation Term is used to refer to two different states Winter sleep = shallow hibernation Slightly lower body temperature Slightly lower metabolic costs Most physiological functions continue normally Characteristic of bigger mammals Skunks, beavers, bears True or deep hibernation Dramatically lowered temperature setpoint Dramatically lower metabolic cost Profound metabolic suppression Characteristic of smaller mammals < 200 g. Biggest example are marmots (~8 kg)

    18. 18 Arctic ground squirrels Spend 6-7 months a year in obligate (=non-optional!) hibernation Body temperatures dip below zero and show very slight supercooling before the thermostat kicks on the heat. Thermostat is ON, just turned WAY down Takes intense 12-15 hours of shivering to arouse, they do this every 2-3 weeks. (VERY expensive) Lots of research on these guys here at UAF!

    19. 19 Temperature setpoints Thermostat = anterior and posterior hypothalamus Both endotherms and ectotherms have thermostats Heating or cooling an animals hypothalamus will induce strong thermoregulatory responses: If heated Panting and vasodilation, shade seeking behavior If cooled Increase in metabolic rate, vasoconstriction, shivering, basking behavior Inputs = temperature sensitive neurons brain, spinal cord, sites in body core, skin (peripheral)

    20. 20 Temperature setpoints These can be variable Day vs. night core temperature varies by 1-3şC In nocturnal animals, night temperature is higher In diurnal animals, day temperature is higher Decreased setpoint = energy savings Fever represents a controlled increase in setpoint In birds and mammals, ranges from 1-4şC In ectotherms, can be much higher Test response using “pyrogens” – bacterial antigens Hibernation and torpor are dramatic changes in setpoint

    21. 21 Adjusting heat production Muscle activity Voluntary Involuntary – shivering Lots of animals shiver … even (occasionally) ectotherms!

    22. 22 Endothermic insects

    23. 23 Adjusting heat production Muscle activity Voluntary Involuntary – shivering Lots of animals shiver … even (occasionally) ectotherms! Non-shivering thermogenesis Metabolic pathways that don’t produce anything Way to use metabolic fuel to make heat Brown adipose tissue Leaky membranes

    24. 24 Who has it? Infants, small mammals, hibernators What is it? Specialized adipose tissue (fat) Highly vascularized (lots of blood supply) Packed with mitochondria (hence “brown”) WHY? It breaks down triglycerides to make heat, and only heat! (NOT ATP!) Brown Adipose Tissue

    25. 25 Brown Adipose Tissue

    26. 26

    27. 27 ATP production in normal mitochondrion

    28. 28

    29. 29 Uncoupling protein (UCP)

    30. 30 Might UCP be a mechanism for endothermy?

    31. 31 ENERGETICS

    32. 32 The Cost of Living

    33. 33 For example

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