LS2_lect30_thermoreg

LS2_lect30_thermoreg - LS 2 Lecture 30 Readings Chapter 13...

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LS 2 Lecture 30 November 17, 2010 Prof Daniel E. Lieberman Office hrs: Tuesday 1-2, & by appt. Peabody 53 Readings: Chapter 13
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Most cellular functions in your body have a limited temperature range 33 34 35 36 37 38 39 40 41 . . . . . . . . . Proteins denature Enzymes deteriorate Membranes lose integrity Etc… Not enough O 2 Reactions slow Etc… General rule: ! 10°C " ! 2-3x VO 2
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Fishes Amphibians Birds Mammals ‘Reptiles’ Ectotherms* Endotherms (Heat source: outside ) (Heat source: inside - metabolism) Dinosaurs endothermy high energy strategy : more active & broader habitat range ? *Also called poikilotherms (changing temperature) economical strategy: limits heat gradient with environment (especially in aquatic animals with gills/cutaneous respiration) Not all animals keep a constant body temperature (T b )
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Why do birds and mammals maintain a constant body temperature (T b ) " 35° C? Birds: 40 C Monotremes: 30 C Marsupials: 35.5 C Mammals: 37-38 C Clue: what is a more favorable gradient? T b < T air or T b > T air ? (is it easier to dump or gain heat?)
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1. Principles of thermoregulation 2. Keeping warm 3. Keeping cool 4. Human adaptations
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Some basics : Heat is energy; temperature is a measure of heat 1 calorie = energy to raise 1 gram water by 1°C (1 joule = 0.239 cal) Specific heat capacity = calories to raise 1 gm of a substance by 1° C Most animals’ specific heat capacity = 0.8 C Body temperature average = 37°C, but variable Core vs periphery Circadian rhythm
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Homeostasis: regulation of a constant T b Core vs peripheral sensory neurons Unmyelinated nerve endings in skin and other organs sense ! temperature Send information to brain via ascending pathway Thermosensory receptors in hypothalamus sense temperature in blood from core Core Periphery
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temperature ‘set-point’, T set (normally 37 ° C for humans & mammals) Brainstem Hypothalamus Pituitary cerebellum blood flow: ! heat neural response (sympathetic and voluntary) Feedback & sensor-effector control of body temperature See text Fig. 16-18 (pg 442 ) Blood flow heat to or from hypothalamus affects T hypothalamus if T hypothal < T set : hypothalamus stimulates heat production (shivering & activity) & reduces heat loss (peripheral vasoconstriction) if T hypothal > T set : hypothalamus stimulates heat loss (sweating & vasodilation) & reduces heat gain (move to shade, reduce activity) ‘thermosensory’ neurons
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Fever: increase in T set
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