Lecture#26 03222024.pdf

ANIMAL PHYSIOLOGY II SC/BIOL 3070 - 4.0 Thermoregulation Suggested readings: Sherwood et al. pgs. 730-756 Thermoregulation 1 Outline Learning Objectives: Introduction: temperature dependence of metabolic rate Temperature classification of animals Mechanisms of thermoregulation Ectotherms Heterotherm...

ANIMAL PHYSIOLOGY II SC/BIOL 3070 - 4.0 Thermoregulation Suggested readings: Sherwood et al. pgs. 730-756 Thermoregulation 1 Outline Learning Objectives: Introduction: temperature dependence of metabolic rate Temperature classification of animals Mechanisms of thermoregulation Ectotherms Heterotherms Endotherms Thermoregulation 2 Introduction Physiological processes are temperature-dependent: - temperature alters the rate of enzymatic reactions – kinetic energy is rate enhancing while denaturation yields destructive effects Thermoregulation Fig. 15-7, p730 - temperature also alters cell membrane fluidity, which is essential for the function and integrity of cells (e.g. transport, diffusion, etc.) 3 Introduction range of temperatures occurring on the earth and the thermal limits for animal life note how Tb differs between endotherms and ectotherms Thermoregulation 4 Determinants of body heat and temperature Thermal energy balance of an animal (i.e. total heat content): = metabolic heat + heat transferred with environment Fig. 15-11, p734 Fig. 15-11, p734 Thermoregulation 5 Determinants of body heat and temperature How is heat transferred? 1) conduction: transfer of heat from a warmer to a cooler object by direct contact (e.g. heat flow from skin to cooler ground or water) 2) radiation: transfer of heat from a warmer to a cooler object by electromagnetic “heat” waves; no direct contact between objects Similar to Fig. 15-12, p735 Thermoregulation 6 Determinants of body heat and temperature How is heat transferred? 3) convection: transfer of heat by air currents; cool air warmed by the body rises and is replaced by more cool air. (e.g. enhanced by wind) 4) evaporation: conversion of liquid such as sweat into a gaseous vapour; heat of vaporization is absorbed from the skin 5) heat storage: influenced by three factors…. Thermoregulation Similar to Fig. 15-12, p735 7 Determinants of body heat and temperature How is heat transferred? 5) heat storage: - influenced by three factors: (a) surface area: smaller animals take up heat and release it more quickly than larger animals (i.e. have greater surface area:volume) - metabolic rate is inversely related to body size ➥ i.e. the smaller the animal, the higher their massspecific metabolic rate Thermoregulation Fig. 15-3b, p721 8 Determinants of body heat and temperature How is heat transferred? 5) heat storage: - influenced by three factors: (b) temperature gradient: the larger the temperature difference between an animal and its surrounding environment, the larger the temperature gradient (therefore, more heat transfer) Thermoregulation 9 Determinants of body heat and temperature How is heat transferred? 5) heat storage: - influenced by three factors: Substance (c) specific heat conductance: ➥ animals with high heat conductance have body temperatures that fluctuate with the ambient environment ➥ animals with low heat conductance maintain a constant body temperature and typically possess insulation (e.g. feathers, fur, blubber, fat) that reduces the temperature gradient Thermoregulation Copper Ice Concrete brick Water Fatty tissue (without blood) Wood Snow (dry) Wool Down feathers Air Styrofoam Thermal conductivity k (J/s⋅m⋅ºC) 390 2.2 0.84 0.6 0.2 0.08–0.16 0.10 0.04 0.025 0.023 0.010 10 Mechanisms for regulating heat transfer 1) behavioral modifications: moving to another environment that favours an optimal body temperature 2) internal physiological adjustments: autonomic changes in blood flow or sweating 3) morphological changes: alterations in the pelage or insulation Thermoregulation 11 Temperature Classification of Animals Temperature classification can be based on: 1) body temperature (a) poikilotherms: animals in which the body temperature fluctuates; - usually body temperature varies as a result of changes in ambient environmental temperature homeotherm poikilotherm Eckert Fig. 17-9 Body temperature (Tb) (b) homeotherms: animals capable of maintaining body temperature above or below ambient temperatures; regulate temperature within a narrow range; active in both cold and warm surroundings Thermoregulation 12 Temperature Classification of Animals Temperature classification can be based on: 2) source of stored heat in the body (a) ectotherms: animals that rely on environmental sources of heat (b) endotherms: animals that generate their own body heat through metabolism (c) heterotherms: animals capable of some endothermic heat production, but do not always regulate their body temperatures within a narrow range Thermoregulation Eckert Fig. 17-11 13 Thermal Regulation in Ectotherms General Ectotherm Characteristics: ➥ obtain heat from the external environment ➥ do not produce enough metabolic heat ➥ poorly insulated (metabolic heat quickly lost) ➥ high thermal conductance ➥ have ‘preferred or selected’ body temperatures ➥ regulate body temperature primarily through behavioral mechanisms Thermoregulation 14 Thermal Regulation in Ectotherms Ectotherms in Cold Environments: - water is the most abundant molecule in cells, accounting for 70% or more of total cell mass ➥ ectotherms living in areas where temperatures are freezing, are at a great risk for ice crystal formation, which can rupture and destroy cells! Three broad strategies used by animals to prevent/tolerate intracellular ice formation: 1) freeze-tolerance - animals that can cope with extensive freezing with ice crystals forming within the body 2) antifreezes - lower the freezing point of the ECF; function as a cryoprotectant 3) supercooling - a liquid cooled below its freezing point without solidifying Thermoregulation 15 Thermal Regulation in Ectotherms Ectotherms in Cold Environments: 1) freeze-tolerant animals - preemptive ice crystal formation ➥ ice crystals that form outside cells do little damage ➥ extracellular fluids (ECF) contain an agent that accelerates nucleation (i.e. initiation of ice crystal formation) ➥ ice crystals form in the ECF but not in the intracellular fluids (ICFs) ➥ solutes are excluded from the ice crystals, so the ECF becomes concentrated ➥ water is drawn out of the ICF due to osmosis, lowering its freezing point and keeping it unfrozen Thermoregulation Eckert Fig. 17-14a 16 Thermal Regulation in Ectotherms Ectotherms in Cold Environments: 1) freeze-tolerant animals - preemptive ice crystal formation Limitations of this strategy: ➥ if Ta falls far below freezing, eventually too much water leaves the ICF and cell organelles are destroyed by the elevated solute concentration Eckert Fig. 17-14b - animals that use this strategy include most invertebrates (e.g. insects) and a few vertebrates (e.g. frogs) Thermoregulation 17 Thermal Regulation in Ectotherms Ectotherms in Cold Environments: 2) antifreezes a) colligative antifreezes (e.g. glucose, glycerol, trehalose, sorbitol, mannitol) ➥ accumulate in high concentrations (0.2-2 M) in body fluids raising the osmotic concentration, which lowers ECF freezing point ➥ limiting the amount of total body that is turned into extracellular ice - animals that use this strategy include arthropods (e.g. insects), arctic ice fish and some amphibians Wood Frog Thermoregulation 18 Thermal Regulation in Ectotherms Ectotherms in Cold Environments: 2) antifreezes - freezing in the wood frog (Rana sylvatica) where up to 65% of body water is converted into ice ➥ initial ice formation in outer skin signals massive glycogenolysis in the liver causes blood glucose concentrations to increase over 450-fold ➥ frog organs become loaded with glucose that serves as a compatible cryoprotectant ➥ increased intracellular glucose helps to keep ICF in osmotic balance with increasing osmolarity in the ECF (due to ice formation) Thermoregulation 19 Thermal Regulation in Ectotherms Ectotherms in Cold Environments: 2) antifreezes - freezing in the wood frog (Rana sylvatica) where up to 65% of body water is converted into ice - thermal camera images: all body regions of frog thaw simultaneously ➥ even thawing ensures blood flow to tissues can start promptly ➥ as frogs thaw, glucose is immediately used to generate ATP Thermoregulation 20 Thermal Regulation in Ectotherms Ectotherms in Cold Environments: 2) antifreezes b) non-colligative antifreezes - occur at lower concentrations (