Lecture 2 Flashcards
Instead of warm blooded, what is a more appropriate term for mammals
Endothermic (from within)
Instead of cold blooded, what is a more appropriate term for reptiles and fish
Ectothermic (outside)
Define endotherms and give an example
maintain their body temps in a narrow range that is mostly dependent on the metabolic rate
e.g. humans n other mammals
Define ectotherms and give an example
have body temps that depend on external heat sources, usually the sun, allowing a wider range of body temperatures; mostly
behavioral temp regulation
e.g. alligator lying in the sun
Define poikilothermic? Example?
- means varied + thermic;
- generally reptiles and fish that use BEHEVIOUR to REGULATE body temp
Define homeothermic? Example?
- similar + thermic;
- generally for mammals whose metabolism, via the autonomic nervous system and behavior, are used to regulate body core temp e.g. shivering
Define energy, its types, and units.
- Energy: The ability to do work.
- Types: kinetic and potential.
- Units are Joules, calories
How can energy in a system or some object be quantified?
Measure potential energy thru mass and velocity. Will be using simple Q.
Define heat. How can heat in a system or in some object be quantified?
Energy transferred from one system to another as a result of thermal interactions
- Quantified as the net amount and direction of transfer (units in Joules/time or Watt).
- Flow from hot to cold
Define temperature. How can temp in a system or in some object be quantified?
- Degree or intensity of heat in environment or object.
- Units: Celsius, Farenheit, Kelvin.
- Measured: thermal expansion coefficient. As mercury goes up or down, water/substance expands and contracts and its thermal expansion coefficient is proportional to temperature.
- Temperature has MAGNITUDE but NO DIRECTION
What is Heat Exchange? What is thermal
energy?
Heat exchange: Transfer of nrg from two physical systems, specifically thermal nrg (kinetic nrg of molecules which can be inc with heat).
- Thermal nrg: example of kinetic nrg, due to motion of particles
What is heat flow and is it directional?
- Heat flow: movement of thermal nrg between two objects, directional where by moves from hotter object to cooler object.
- Heat flow has magnitude n direction, heat exchange is a to descriptor (convection, conduction, radiation)
- Flow can be thought of as mass of energy transferred over timed. Heat exchange is used to describe process
Difference between temp and heat?
HEAT vs. TEMP… HEAT IS DIRECTIONAL AND HAS MAGNITUDE
What are the avenues for heat exchange (5)
(Bi-directional)
- Conduction
- Convection
- Radiation
- Evapouration
- Metabolic heat generation (aka transfer)
What is conduction (QCD)?
direct contact of 2 objects gives heat transfer
What does conduction depend on? (3)
- depends on temp difference from body (Tb) to skin surface (Ts)
- area of contact
- conductive properties of the 2 materials
How does fat/muscle/fur affect conduction
- conduction varies w/fat n skeletal muscle insulation in humans n fat/fur in animals
- fat is a much poorer insulator than a few cm of fur like in a down jacket.
- insulation of fur and clothes is mainly due to trapping of air (best insulator)
What is the equation to calculate conduction
Two possible eqns:
QCD (W x ºC^-1 x cm-1 ) = kA(T2-T1)/d
Where:
A = area of contact
d = distance btwn 2 temps T1 & T2
k = thermal conductivity (units of J x s^-1 x ºC^-1 x cm^-1)
But since d and A hard to measure, use:
QCD (W x ºC^-1) = C x ΔT(2-1)
Where:
ΔT2-1 = thermal gradient
C = thermal conductance heat transfer
coefficient (W x ºC^-1)
What is thermal conductivity (k)? What is it directly related to
a fixed property of materials and is directly related to insulation
What is insulation
reciprocal of total heat flux per unit area per unit of temperature difference (ºC x cm^-2 x sx J^-1)
What is “clo”
- clothing unit
- when insulation is given per m^2
How much is 1 clo?
0.16ºC x m^2 x W^-1
What is tissue thermal resistance (r, s x cm^-1) vs. tissue thermal conductivity?
- In bio or physiology, a tissue layer can be expressed as RESISTANCE
- Takes into account thermal CONDUCTIVITY (k) and adds the THICKNESS (l) of the layer
Eqn for thermal resistance (r)? What are the units
r =(ρ x Cp x l) / k
OR
k =(ρ x Cpx l) / r
Where: ρ x Cp = specific heat capacity of the medium, i.e. air or water;
density (ρ) = mass/vol of the layer.
What is specific heat capacity
heat required to raise the temperature of the unit mass of a given substance by a given amount (usually one degree).
aka more nrg needs to be put in to inc temp = higher specific heat capacity
What is the relationship between resistance and thermal conductivity?
Reciprocal relationship
What is convection (QCV)?
Movement of a gas or liquid over or within a body resulting in heat exchange
What does convection depend on? (4)
- temp. difference TS to TAIR
- body dimensions
- curvature of body surface
- the fluid or gas:
• thermal expansion coefficient
• density
• viscosity
• velocity
What is the thermal expansion coefficient units?
change in length/ºC increase
Example of convection? (3)
wind against body; running water over body surface, human blood
Eqn for convection (QCV)?
QCV (W x m^-2 x ºC^-1)
= C x A x (TSKIN - TAIR)
Where: A = area, C = h(c) =
convection heat transfer coefficient
Of the factors influencing convection, what is most important?
Air speed or velocity
Convective heat exchange varies ~ as the square root of air velocity EXCEPT?
At very low velocities
Similarity btwn convective heat transfer coefficient h(c) and evapourative heat transfer coefficient h(e)? Difference?
Both convection and evaporation strongly dependant on air speed/velocity
- Convection also dependent on fluid velocity but not evapouration
What is radiation?
• heat transferred at the speed of light
• is emitted from all bodies
that have a temperature >
absolute zero or -273ºC
Wavelength of radiation depends on? (2)
- difference btwn surface temp of the emitting bodies [skin temp (TS ) and object surface (TSUR)]
- characteristics of the surface area of a body or object including it’s EMISSIVITY and SHININESS
What is I(MAX)?
Predominant wavelength of radiation from a body
How is I(MAX and T(SUR) related?
I(MAX) is inversely proportional to T(SUR) (Wien’s Law)
What is reflectance
- ratio of the INTENSITY of REFLECTED to INCIDENT radiation on a surface
- bidirectional
What is emissivity (ε) of a body?
ability of body to emit energy by radiation.
- is a DIMENSIONLESS constant for any material = ratio of nrg emitted by that body to that emitted by a black body at the same temp; is unidirectional.
- is related to the familiar concepts of COLOR and SHININESS of the surface
- biological materials have ε in medium to long IR radiation with values btwn 0.90 and 0.99
What is a “perfect” black body? How does this compare to a mirror?
an ideal emitter and; gives off ≥ energy than any other body and has ε=1 vs. mirror or perfect reflector has an ε = 0.
What is Evaporation (QE)
is heat loss due to the evaporation of
sweat/H2O from surface of the human body
What is the most effective heat loss from the human body
QE (Evaporation)
What factors do Evaporation (QE) depend on
- same factors as for convection 1. temp. difference TS to TAIR 2. body dimensions 3. curvature of body surface 4. the fluid or gas: • thermal expansion coefficient • density • viscosity • velocity
plus some additional: 1. surface temp 2. H2O vapor density between surface and surrounding air 3. resistance to H20 loss by the surface
What is the latent heat of evaporation
- gas to liquid phase
- latent heat of evaporation
is 2400-2500 J/g H20
What is the eqn for evapouration
QE (W x m^-2 x kPa) = C x A x (PSKIN-PAMB)
Where: A = area, C = he = evaporation heat transfer coefficient, PSKIN
skin water vapour pressure, PAMB = ambient water vapour pressure
What happens to eqn for evapouration when skin surface is completely wet
If skin surface is completely wet, skin water vapour pressure = saturation water vapour pressure for that skin temp. Then QE is maximum (QEMAX) for those environmental conditions.
QEMAX (W x m-2 x kPa) = C x A x (PSKIN,SAT - PAMB)
Where: PSKIN, SAT = Saturation water vapour pressure
What happens to eqn for evapouration when skin surface is not completely wet
If skin surface not is completely wet, a skin wettedness coefficient (w) is used = ratio of QE/ QEMAX, with 0 ≤ w ≤ 1
QE (W x m^-2 x kPa) = C x A x wQE x (PSKIN, SAT - PAMB)
Wettedness depends on hydration ____ and fraction of _____ that is wet
Wettedness depends on hydration EPIDERMIS and fraction of SKIN that is wet
What is Relative Humidity (RH):
For a certain air temp there is a given capacity for H2O vapor
Rqn for RH
actual water vapor / water vapor capacity for given temp
DEC air temp = ____ air vapor capacity
DEC air temp = DEC air vapor capacity
INC air temp = ____ air vapor capacity
INC air temp = INC air vapor capacity
RH is ______ related to evaporation from the skin. e.g. in a cold environment, Pa will be ____ enough that sweat can easily evaporate from the skin even if ____ = 100
RH is INDIRECTLY related to evaporation from the skin. e.g. in a cold environment, Pa will be LOW enough that sweat can easily evaporate from the skin even if RH = 100
How is wet bulb temp diff from dry bulb temp
WBT = DBT when air is saturated w/water
What is dew point temp (DPT)
is the DBT at which a moist air sample at the same pressure would reach water vapor saturation
What is metabolic heat production (QM)? What is the heat produced proportional to
- when a fuel is oxidized or burned up, heat is
liberated from the body - the amt of heat liberated is proportional to type of fuel oxidized and rate of metabolism
For metabolic heat production (Qm), how does the heat produced vary with whats oxidized?
- heat produced varies with proportions of fat/CHO oxidized (INC fat oxidized = INC heat produced)
For metabolic heat production (Qm), how can it be estimated?
- estimated by direct and indirect calorimetry
- efficiency of energy transfer
What is the Rate of Heat Exchange (S)
this is the net of the different rates of heat exchange via the different avenues
Eqn for Rate of Heat Exchange (S)
S = +QM +/- QCD(Tb-Ts) Qconv(Ts-Ta) +/- Qrad(Ts-Tsur) -QE(PSKIN-PAMB)
Where:
Qx x ΔT= rate of heat exchange, where x = avenue of heat exchange
and ΔT = difference in temperature
- Qx= heat transfer coefficient for that avenue of heat exchange
- Tb = temperature of body contacting the skin
- Ts = skin temperature
- Ta = air temperature
- Tsur = temperature of an object emitting radiation
- P = Pressure
What is the 1st line of defence to a change in ambient temp.
Behavioral Responses
Example of Behavioral Responses to Changes in Body Temperatures
- In hot/cool climates we choose appropriate clothing, activities, and locations to minimize the changes in our body temp
e. g. in deserts we look for shade, drink water, wear shorts and sandals
e. g. in winter we stay inside, are more active to generate heat, wear warm insulated clothing
What is Hyperthermia
inc of core temp by ~1ºC above resting normothermic levels
What is hypothermia
dec in core temp by ~1ºC below resting normothermic levels
What is vasodilation
Inc in caliber of a blood vessel
What is vasoconstriction
an actively mediated dec in peripheral BF by various mxn(s)
What is vasomotion
changes in caliber of vessels by vasoconstriction or vasodilation actions
What are arteriovenous anastomoses (AVAs)
Direct arterial to venous conduit in a capillary bed that connects arterioles and venules; allows bypassing of capillary beds; useful for heat conservation in cold climates
What are the diameter of capillaries vs. AVAs
Capillaries = 5-10µ, AVA 20-70µ
What are eccrine sweat glands
produce sweat that is employed in body cooling after increases in body temp
What are apocrine sweat glands
produce sweat often after an emotional event
What is a set point
– point of core temps about which core temp is regulated
What is null zone
a zone of core temp with no sweating or shivering and just vasomotion
What is core temp? How can it be measured
– temp of the bodys core, usually measured in the esophagus, GI tract, rectum or on the tympanic membrane
What is skin temp
– temp on the surface of the body, usually measured w/a thermocouple or thermistor taped to the skin surface at multiple sites
What is the periphery
– describes the peripheral tissues; there are
no definite boundaries for the periphery; and its size inc or dec depending on the peripheral vessels states
What is the core
– describes the central tissues, there are no definite boundaries for the core and its size inc or dec depending on the peripheral vessels states
What is the Hypothalamus
centre for temp regulation
What are cold sensitive neurons
dec’s in their temps cause inc firing rates
What are Warm sensitive neurons
inc in their temps cause inc firing rates
Discuss the control of room temp when there is a disturbance (include what is the receptor, control centre, effector)
E.g. if room temp rises, the thermometer (RECEPTOR) located inside the thermostat (CONTROL CENTER) sends this info to the thermostat which sends the command of the AC (EFFECTOR) to turn on. A thermostat stabilizes room temp by turning on AC (or heater) as needed to keep room temp near desired set point. When room temp rises, thermostat turns on AC, and room temp returns to normal lvls. With this regulatory system room temp oscillates around set point
Describe the POAH (its neurons inc in firing due to? how is the output inhibited?)
- has neurons that inc in firing with increased temp = stimulates heat loss
- this output is inhibited by cold input from skin
Describe the DMPH (its neurons inc in firing due to? how is the output inhibited?)
has neurons that increase in firing with dec temp
- this output is inhibited by warm input from skin
As core temp drops, metabolic rate ____
As core temp drops, metabolic rate INC
Who identified a null zone of core temp with no sweating or shivering responses
Mekjavic
What are responses to cold environment
- shivering (inc metabolic rate) and vasoconstriction
- sympathetic response to catecholamines via ß1 and
ß2 receptors; also thyroxine over long term increases metabolic rate - Non-shivering thermogenesis
What is involved in non shivering thermogenesis and what receptor? Researcher who discovered this
- brown adipose and other tissues via ß3 receptors
- uncoupling proteins UCP1, UCP2 and UCP3
- J. Himms-Hagen /Mary-Ellen Harper in Ottawa
In regulation of Regulation of Body Heat Content, what does the time constant (tau) represent
– represents the time it takes a system’s step response to reach 1-1/e that is approximately 63.2% of its final asymptotic value
Describe indirect calorimetry
Computer interfaces with:
- A flow-measuring device that records air volume breathed
- O2 and CO2 analyzers that measure the composition of the expired gas mixture
- Mouth piece/nose clip or hood
