Temperature Regulation.Pdf

C H A P T E R 13

Thermal Physiology

PowerPoint® Lecture Slides prepared by Stephen Gehnrich, Salisbury University

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

(5 weeks)

“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.

All six species have about the same enzyme-substrate affinity when they are at their respective body temperature.

Eurythermal species

Stenothermal species

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)

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

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

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

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

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

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

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

Poikilothermic animals Homeothermic animals

Ectothermic animals Endothermic animals

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

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)

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

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

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

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

Figure 13.18 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 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

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

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

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

The brain temperature may be 2~3 ℃ lower than core body temperature

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)