Module 1: Heat Transfer + Thermoreg. Flashcards
Heat
Kinetic energy embedded in molecules (molecular motion)
Temperature
An index of molecule motion (the average kinetic energy)
–> Hot = High KE
–> Cold = Low KE
Heat Transfer
The movement of heat energy from one place/material to another
–> Occurs wherever there is a temperature difference
–> Has 4 main methods
Methods of Heat Transfer (4)
1) Conduction
2) Convection
3) Radiation
4) Evaporation
Conduction
Heat transfer through STATIONARY matter by PHYSICAL CONTACT
Driving Force of Conduction
Temperature gradient (difference in temp between the two objects)
T1 > T2
Heat flows from T1 to T2
T1 < T2
Heat flows from T2 to T1
T1 = T2
No NET transfer; heat is still transferring between the two but it is just occurring at an equal rate in opposite directions
Heat always flows from…
High temp (heat content) to Low temp (heat content)
Rate of Heat Transfer Equation
(and simplified form)
dQ/dt = [(K*A)/ L] * [T2 - T1]
Flow = Ease of Movement * Driving Force
Ease of Movement
The physical constraints to flow of substances (Determined by physical characteristics)
Ease of Movement (part of the equation)
(K*A) / L
What is “K” in the heat flow equation?
K = Thermal Conductivity (of the material)
What is “A” in the heat flow equation?
A = Surface area of contact
What is “L” in the heat flow equation?
L = Length/distance between objects
Convection
The transfer of heat from one place to another due to the movement of fluid/air
A modified form of conduction in which one or more of the units can move relative to each other
Two main types of convection:
1) Forced Convection
2) Free Convection (AKA “Natural”)
–> Differentiated by how the movement of the object/s is initiated
Free Convection
Environmental medium movement is caused by natural means
(passive movement)
(Ex: Hot air rising)
Forced Convection
Environmental medium movement is externally/physically induced
(Ex: Fan moving the air)
Heat flow of free and forced convection differ mainly in their…
DRIVING FORCE (temp. gradient)
Free Convection: Much less heat transfer due to the formation of boundary layers
Forced Convection: Much more heat transfer due to the disruption of the formation of boundary layers
Effect of boundary layers on convection
Boundary layers decrease the TEMP GRADIENT between two mediums
Ex: Air around the body DOES NOT = the environmental temp as the air directly around the skin has a slightly higher temp due to heat loss from our bodies going into the air (warming it up)
Radiation
Electromagnetic Waves
–> All objects both ABSORB and EMIT electromagnetic waves
Heat Loss from Radiation
If an object has KE, some of that energy will radiate away from the object
Heat Gain from Radiation
If electroneg. radiation coming down as thermal energy hits a surface, it can absorb (gain) that energy
Evaporation
The transformation (of water) from liquid to gas
Heat of Vaporization
Evaporation requires energy (heat of vaporization)
–> Will pull heat from whatever the substance is on to transfer from liquid to gas, “taking the heat with it”
Evaporative Cooling
As water moves from liquid to gas, it absorbs heat from the body and carries it away in its gaseous form = HEAT LOSS
–> Evaporation only leads to HEAT LOSS; never heat gain
Thermal Budget
A concept referring to the balance between heat gain and loss overtime to maintain a relatively constant body temperature
Heat gain = Heat loss
Heat gain mechanisms
**External Exchange: **
1) Conduction
2) Convection
3) Radiation
**Internal: **
4) Metabolic Rate (endogenous heat production)
Heat loss mechanisms
External Exchange:
1) Conduction
2) Convection
3) Radiation
4) Evaporation
Internal:
N/A
Thermoregulation
The maintenance of physiological core body temperature by balancing heat generation with heat loss
Why must body temperature be regulated?
So that rxns. occur at a sufficient rate
If body temperature is too high…
Enzymes needed for rxns. denature and biochemical pathways fail = Death
If body temperature is too low…
Enzyme activity slows/stops due to insufficient KE to cause enzyme-substrate collisions
Maintaining body temp at a specifific optimal temp allows…
For enzymes to function at a rate efficient enough to meet cellular demands without having a temp that is too high/low that stops/slows enzymatic activity
Reaction Rate and Temperature Relationship
Reaction rate increases exponentially with temperature increase
3 main strategies for thermoregulation:
1) Ectothermy
2) Endothermy
3) Heterothermy
Ectothermy
Use of external heat to thermoregulate; body temp varies WITH environmental temp
AKA “Poikilotherms”, “Cold Blooded”, “Variable Tb”
Organisms that are Ectotherms
1) Reptiles
2) Amphibians
3) All non-vertebrate species (insects/crustaceans)
4) Fish + sharks
In ectotherms, body temp is ____________ to environmental temp
PROPORTIONAL
Tb = Tamb
Ectotherms: Metabolic rate and environmental temp relationship
MR varies with Tamb
Ectotherms: High environmental temp
= High MR, animal is faster, > need for energy
Ectotherms: Low environmental temp
= Low MR, animal is sluggish, < need for energy
Advantages of Ectothermy (3)
1) Requires less energy
–> Don’t need to increase MR to regulate body temp
–> Can let biochem processes slow down
–> For this reason, can go longer without food
2) Can exploit broader range of body sizes/shapes
–> Have freedom from heat-conserving body constraints
–> Can be very small
3) > Efficiency producing biomass
–> > amount of produced energy can go to building biomass rather than generating heat for maintaining temp
Ectotherm Thermoregulation Strategy
Mainly Behavioral Thermoregulation
–> Will search environment for optimal temp
Goldfish Thermoregulation Example
1) Goldfish placed into water tank with area of different temps
2) Goldfish explores tank
3) Selects region with the preferred temp and stays there
Anole Lizard Thermoregulation Example
1) Sits on rock in sun to warm up during the day (Body temp can get higher than environmental temp!)
2) Burrows to prevent heat loss at night
Terrestrial ectotherms deal with greater __________
Temperature fluctuations
(than aquatic ones since aquatic ectotherms have body temp directly equal to water temp)
Thermal Acclimation
A physiological response that helps organisms adapt to LONG TERM temperature changes
Maximum Critical Temperature
CTmax = Temp at which biochemical processes begin to fail (peak of the MR curve)
Thermal Acclimation in Ectotherms
Can change their CTmax through selective enzyme synthesis
–> Produce different isoenzymes with varying optimal temps
Isoenzyme
Related forms (isoforms) of the same enzyme
–> Catalyze the same rxns under different conditions
Summer vs Winter Isoenzymes
Summer: Produce Isoenzymes with HIGHER optimal temp
(> CTmax)
Winter: Produce isoenzymes with LOWER optimal temp
(< CTmax)
Acute Response
Rapid temp change = Rapid MR change
Chronic Response
MR SLOWLY increases or decreases to optimal MR as new proteins with an optimal temp of the new environmental temp are produced
Thermal acclimation involves TWO types of responses
1) Acute response
Followed by,
2) Chronic response
ONLY IF TEMP CHANGE REMAINS CONSTANT LONG TERM
Endothermy
Use of INTERNAL heat to thermoregulate
Body temp remains relatively constant no matter the ambient temperature
Relationship between body temp and ambient temp in endotherms
Body temp is NOT equal to ambient temp –> It is INDEPENDENT of environmental temperature
Thermoneutral Zone
Range of AMBIENT TEMPS over which organism can thermoregulate WITHOUT increasing the MR
How is body temp regulated in the TZ?
Through physiological changes such as vasodilation/constriction and other behavioral changes –> DO NOT increase MR!
Vasoconstriction is best utilized for…
Heat retention; when it is colder outside
It INcreases the distance between the blood vessels and the heat exchanging surface
Vasodilation is best utilized for…
Heat loss; when it is warmer outside
It DEcreases the distance between the blood vessels and the heat exchanging surface
Thermogenesis (and the 2 main types)
Conversion of chemical energy into HEAT
2 main types:
1) Shivering thermogenesis
2) NON-Shivering thermogenesis
Shivering thermogenesis
The co-contraction of muscles all over the body to generate A LOT of heat (as muscle contraction is highly inefficient with 75% of the energy expended being dissipated as heat)
Non-Shivering thermogenesis
Metabolism of fat (mainly brown fat) to produce heat
Endotherms utilize mechanisms of thermoregulation in TWO main categories…
1) Thermogenesis
2) Altering thermal conduction
5 main processes utilized to alter thermal condutcion in endotherms
1) Decrease surface area (Available for heat transfer)
2) Increase size of organism
3) Insulation (fur/fat)
4) Decrease driving force (temp gradient)
5) Avoidance (behavioral regulation)
