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Flashcards in Thermal Physiology Deck (32):

Q10 and Reaction Rate

-where most reactions occur

-Q10 = 3
-for every 10 deg. C increase, reaction rate triples
-Q10 = 2
-For every 10 deg. C. increase, reaction rate doubles
*Between Q10 =2 and Q10 = 3 is where most biochemical reactions occur

-Most organisms are highly dependent on temperature


What happens when temperature goes outside optimum ranges (either high or low)

-The Van Der Waal's forces holding membrane lipids together are affected by temperature
-Temperature changes membrane fluidity -> affects protein movement
-Low temps cause membrane lipids to solidify
-High temps increase membrane fluidity






-Heat: Total kinetic energy of all molecules in system
-any system w/ temp. above absolute zero will contain some heat

-Temperature: Mean kinetic energy of molecules in a system
-Determines the direction of heat flow (from more to less)


Physics of Heat Transfer

-4 methods heat transfer occurs (list)



Total Heat equation

H(total) = H(Metabolic) + H (conduction) + H(Convection) + H(radiation) + H(evaporation) + H(stored)

*can rearranged so equation equals Stored heat (just remove H(total))


Conduction -> Definition

-4 things it is influenced by

-Conduction: Movement of heat from high to low temperature by interaction of adjacent molecules
-Influenced by;
-Thermal Conductivity (k)
-Area (A) through which heat flows
-Temperature gradient
-Separation distance


Convection -> Definition

-2 things it is influenced by

-Convection: Movement of heat through a fluid (liquid or gas) by mass transport in currents
-Influenced by:
-Temperature Gradient
-Convection coefficient (which is dependent on body shape (i.e. SA), wind speeds (or water current))


Radiation -> Definition

-2 things it is affected by

-Radiation: energy transfer by means of electromagnetic energy - travels at speed of light and needs no medium of propagation
-Influenced by;
-Absolute Temp.
-Surface Area



-Direct and reflected solar radiation (what is dependent on)
-Re-radiated radiation

-Direct and reflected solar radiation;
-in visible range (400-700nm)
-Heat gain affected by colour)
-Re-radiated Radiation;
-mainly in mid infra-red range
-colour is not important for heat loss


Evaporation -> Definition

-4 factors it is influenced by

-Evaporation: Evaporation of water requires a lot of heat (removes that heat from the body)
-Influenced by;
-Temp Gradients
-Vapour pressure gradients
-Surface Area
-Wind speeds


Heat exchange in bodies - what system is used? why?

-Countercurrent Mechanisms used as tissues are poor conductors

*Is a countercurrent multiplier


Thermal Strategies

-Effect of temperature on reactions and performance

-Effect of temperature: as temp increases, no. of molecules that have a high enough activation energy increases (is a max.)
-Effect on performance: Depends on organism, but all have a temperature where performance is maximised


-Based on stability of Stored heat (2 terms)

-Based on source of thermal energy (2 terms)

-Based on stability of stored heat;
-Poikilotherm: Tb changes with Ta (body temp and ambient temp)
-Homeotherm: Regulates Tb by physiological means (NOT just behaviour)
-Based on source of thermal energy:
-Ectotherm: Thermal balance depends on external sources of heat (conduction, convection etc.)
-Endotherm: Thermoregulation depends on metabolic heat production as major source of heat

*animals fall into 4 categories based on whether they display endothermy or thermoregulation


Exceptions to Thermal strategies (2)

-Temporal heterotherms: Undergo prolonged changes in Tb
-e.g. hibernating animals or pythons after a large meal (or female with eggs - increase body temp)
-Regional heterotherms: Retain heat in specific regions of the body
-billfish w/ heat organs near eyes (thru brown adipose tissue)
-Tuna retain myogenic heat within red muscle


Body Temperature and Metabolism: Poikilotherm and Homeotherm

-Poikiotherm: VO2 increases with increase in Ta (= Q10 effect)
-Homeotherm: VO2 decreases with Ta, then independent after critical point (= Thermal neutral zone)



-Thermoneutral zone
-Upper Critical Temperature
-Lower critical Temperature
-Eurythermic and Stenothermic

-Thermoneutral zone: Range of temperatures that are optimal for physiological processes; metabolic rate is minimal
-Upper critical Temp: Metabolic rate increases to induce a physiological response to prevent overheating
-Lower Critical Temp: Metabolic rate increases to increase heat production
-Eurythermic: have a wide thermoneutral zone
-Stenothermic: have a narrow thermoneutral zone


Amphibians and Reptiles vs. Birds and mammals

-Amphibians and reptiles: Ectotherms (low energy approach to life)
-low MR
-Growth and reproduction based on food, water and O2 availability
-elongated and small bodies
-Mammals and Birds: Endotherms
-High MR
-Independent of Ta


Internal Thermostat in Mammals and Birds

-Mammals: thermal sensory information integrated in the hypothalamus
-Birds: thermostat is located in the spinal cord

*are negative feedback systems


Variations in body temperature (4)


-Circadian rhythm of Tb (fluctuates over the day)
-Rise in Tb associated w/ menstrual cycle
-Postmenopausal hot flashes

*causes new set point to be higher - is why we shiver even though hot


Effect of amphetamines on Vertebrate thermostat

-Amphetamines associated with significant morbidity and mortality; largely due to the disturbances it causes in thermoregulation
-In rats; ambient temp 30 deg.: dose dependent hyperthermic action (generate too much heat)
-ambient temp 7 deg.: hypothermic (body temp decreases)


How to increase heat if cold

-3 things that can be done

M + K + C + R + E = Tb
-Can only change 3 things;
1. Heat production (M)
2. Insulation (K + C + R + E)
3. stored heat (Tb)


Heat production


-Non-shivering Thermogenesis (NST)

-Increased Basal Metabolic rate

-Shivering: Uncoordinated skeletal muscle contraction producing heat
-Non-shivering Thermogenesis (NST): Enzyme systems for fat metabolism activated to produce energy (heat)
-occurs in both regular (in cells) and brown fat (intracellular structures - such as many blood vessels) (mitochondrial uncoupling)
-promoted by thyroid hormones
-Increased Basal Metabolic rate: generates energy and therefore heat


Insulation to deal with cold


-2 types (and e.g. of these types)

-What effectiveness depends on

-A layer of material that reduces thermal exchange

-Internal insulation:
-External insulation:
-animals get fluffier when it is cold (Via piloerection)
*effectiveness depends on its thickness


Insulation to deal with cold in wet conditions

-Fur thickness doesn't help when wet
-Blubber used -> beneficial as can control degree of insulation by opening/closing blood vessels


Behavioral changes to deal with Cold (3)

-Huddling (Decreases SA:V ratio)
-Hibernation: seasonal, body temp is a controlled physiological state (used to save energy)
-as it gets cold, decrease set point


Critical Thermal Maximum (CTM)

-definition and what occurs

-Is the maximum temperature that animals can be exposed to, above which long-term exposure can be fatal
-e.g. protein denaturation, decreased affinity of Hb for O2, membranes become fluid


Dealing with heat -> heat balance

-3 things that can be done;
1. Decrease heat production
2. Increase conductance
3. Tb (allow to store more heat)


Conductance to deal with heat

-What animals do

-e.g. altering blood flow to the body surface -> can change the effectiveness of heat exchange
-in heat, can dilate capillaries to allow blood to get under skin
-Most mammals, rise of 0.5 deg. C. causes peripheral vasodilation
-in rabbits, heat loss through ear


Evaporative cooling to deal with heat

-If ambient temp is greater than Body temp, or metabolic production is high, then K + C + R all positive
-need mechanism to move heat against thermal gradient
-Evaporative cooling = 1 g water removes 2.4 kJ of heat


Diurnal Heterothermy to deal with the heat

-Goes through cycles of heating and then decreasing heat -> can allow the body to store heat


Selective brain cooling

-Carotid rete: countercurrent heat exchange
-cool blood from nasal passage passes blood going to brain (e.g. in black wildebeest)
-Is turned off when running; can save on evaporative water loss

-horses also have gutteral pouches - is a countercurrent system for cooling carotid blood


Effect of size on heat (5)

-Height off the ground (elevation decreases heat loading)
-Ability to move to more suitable habitat
-More efficient locomotion
-Thermal Inertia
-EWL would be extreme for small endotherms

-Small mammals rely mostly on behavioural thermoregulation (permanently, daily and periodically)
-e.g. microclimate selection (burrow deep to find low temp soil)

*Larger animals have advantage of size in desert (if they obtain food to sustain them)