Thermal Physiology Flashcards
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)
(4)
- 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
Definitions;
- Heat
- Temperature
- Differences
- 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)
- Convection
- Conduction
- Radiation
- Evaporation
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
Radiation;
- 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
- mainly in mid infra-red range
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
Terminology;
-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
- Ectotherm: Thermal balance depends on external sources of heat (conduction, convection etc.)
*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)
Defintions;
- 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)
-Effect
- Circadian rhythm of Tb (fluctuates over the day)
- Rise in Tb associated w/ menstrual cycle
- Postmenopausal hot flashes
- Fever
*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
- Shivering
- 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
- Definition
- 2 types (and e.g. of these types)
- What effectiveness depends on
-A layer of material that reduces thermal exchange
Types;
- Internal insulation:
- blubber - External insulation:
- Hair
- feathers
- animals get fluffier when it is cold (Via piloerection)
- air
- water - 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)
