topic 8 - thermoregulation Flashcards
what is homeostasis
regulation of an internal environment in the face of change in the external environment
does not imply a constant internal environment
what is negative feedback
change in variable triggers a response that opposes the change
what are the negative feedback mechanisms
stimulus - external or internal change in a regulated factor (ex: temp change)
sensor - detects the change in the condition
integrator - compares condition to the set point and activates effector
effector - a physiological change that returns the factor to the set point
what are the negative feedback mechanisms involved in temp regulation
sensor - temp detection nerves in skin
integrator - hypothalamus (figures out what to do with info it receives regarding temp)
effector - muscle tissue vasculature, sweat glands
oscillation in temp throughout the day
what is positive feedback
change in variable triggers a response that amplifies the change
does not lead to homeostasis (pushes system away from homeostasis)
birth
melting permafrost releasing methane is a positive feedback driving global heating
what is thermoregulation
regulating internal body temp impacts energy budgets
ambient temp (Ta)
body temp (Tb)
Ta (outside temp) determines how much energy is spent regulating body temp
how is heat generated in endotherms
metabolism
how can heat be exchanged with the environment
convection - heat is transferred to and from an organism through air or liquid
conduction - direct contact heat transfer
evaporation - loss of heat when water changes from liquid to gas - change of state is also a loss of heat because energy is required to cause the change
electromagnetic/radiation - from sun hits dark colours and becomes heat
what is the rate of heat exchange
conductance
why do larger organisms have lower conductance
lower SA V ratio
more SA = more conductance
less SA = loses less heat
what is a homeotherm
maintains “constant” body temp independent of body temp
what is a heterotherm
body temp fluctuates with ambient temp (instantaneous or delayed)
what is an endotherm
uses metabolism to generate body heat
what is an ectotherm
acquires body heat from environment (regulate body temp through behaviour)
are there heterothermic endotherms
mole rats only (use huddling strategy and keep body temp low)
almost all homeotherms are endotherms
what is regional heterothermy
animals with different body temps in different parts of their body
what are the characteristics of homeothermic endotherms
behavioural - seek cool or warmth
physiological - sweating, panting, shivering
what are the characteristics of homeothermic ectotherms
seek or live exclusively in stable environments or microhabitats
what are the characteristics of heterothermic endotherms
change in body temp seasonally (torpor, hibernation, or daily)
what are the characteristics of heterothermic ectotherms
behavioural - move between sun and shade
physiological - adjust metabolic rates based on ambient temp
what are the metabolic consequences of endothermy
have a higher mass specific RMR than ectotherms
as mass increases, mass specific MR decreases
endotherms have a higher mass specific MR than ectotherms
why is temp important for metabolism
enzyme activity varies with temp
temp drives metabolism which in turn drives performance
metabolic rate and max speed have similar response curves to temp as enzymes do
what is the relationship between ambient temp and body temp in ectotherms
1:1 - slope of 1
what is a homeothermic endotherms response to changes in ambient temp
animals have to expend energy outside the thermal neutral zone (TNZ) and the amount of energy needed is related to the difference in ambient temp from the TNZ
what is the TNZ
temp of max performance in endotherms
no energy needed for regulation
temp range where metabolic rate is basal
what happens when ambient temp drops below TNZ
metabolic rate increases from resting state to create warmth
what happens when ambient temp goes above TNZ
metabolic rate increases to cool down
what does the slope of the line of RMR v ambient temp represent
slope of the line = animals conductance
what are strategies to regulate temp below TNZ
shivering
vasoconstriction (less blood to periphery)
piloerection (increasing depth of fur)
decreasing SA
decreasing exposure (huddling/burrowing)
thermogenesis
what are strategies to regulate temp above TNZ
panting
vasodilation
sweating
increase SA
decreasing exposure (to sun)
active cooling
what is the benefit of high and low conductance
low (lower slope) = heat retention (arctic)
high (higher slope) = heat loss (tropical)
what is the heterothermic ectotherm response to temp changes
no TNZ for this group
temp approaches optimum for proteins and enzymes (zone of optimal activity)
suboptimal = less activity
what is behavioural regulation of conductance
minimise energy expenditure due to temp
moving to optimise heat exchange with the environment to attain ideal body temp
- changing exposure (seek or avoid)
- grouping (being around others)
- migration (move to change ambient temp)
dormancy (torpor, hibernation)
what is torpor
short (6-8 hour) reduction in activity (~10C - not all the way to Ta) in body temp and a lower metabolic rate
what is the purpose of torpor
reduces energy to stay warm (esp when food is scarce in winter, low food conditions, or drought)
what is hibernation
awake for 1-2 days periodically to release toxic waste (urine) then go back to sleep until winter is over
rapid recovery in body temp = characteristic of hibernation
what is the main difference between hibernation and torpor
body temp drops to neat ambient temp in hibernation
why is small size good for hibernation
large SA V ratio = easy to brin body temp up and down
do bears hibernate
no - winter sleep (more similar to torpor)
low SA V ratio helps them conserve heat
body temp remains significantly above ambient temp (small drop to reduce metabolic rate and conserve energy)
wake up after a short period and excrete waste
what are reasons for migration
temp regulation
ambient temp condition
scarce food
competition
predator avoidance
how is conductance physiologically regulated
acclimation (ecto)
blood flow
insulation
fur length and colour change
sweating and panting
cryoprotectants (ecto)
shivering thermogenesis
non shivering thermogenesis
everything else ^ endo
what are the physiological responses to the temp increase
Message to hypothalamus
Vasodilation
Sweating
Panting
what are the physiological responses to temp decrease
Message to hypothalamus
Brown adipose tissue is metabolised to generate heat quickly
Vasoconstriction
Shivering
what is acclimation
altering optimal temp for performance
changes to physiological processes that respond (typically to seasonal) temp changes
takes a longer time (not instantaneous)
example: how does membrane viscosity acclimate
cold = increased viscosity
- cold acclimation = change phospholipids to be less saturated to decrease viscosity back to set point
hot = decreased viscosity
- hot acclimation = change phospholipids to be more saturated to increase viscosity back to set point
what happens with vasoconstriction
Decreases conductance with environment
Endotherms = when cold to retain heat
Ectotherms = when hot to retain heat
what happens with vasodilation
Increases conductance with the environment
Endotherms = when hot to release heat
Ectotherms = when cold to increase heat gained from environment (hot rocks)
what are internal and external insulation
Internal = fat/blubber
External = fur/feathers
Piloerection - the fluffing of fur/feathers to increase the thickness of insulation
what are the characteristics of dark fur
Absorbs light, generates heat outside insulation - doesn’t reach body as much
Heat lost to environment more easily by convection
what are the characteristics of light fur
Allows light to reach skin, generates heat inside insulation layer
Skin stays warmer as fur protects loss
Some mammals have hollow hairs which let radiation transmit down shaft
Best winter combo = black skin, white fur
how does panting cause heat loss
increases ventilation rate which increases heat loss by evaporation and convection
what are cryoprotectants
used by ectotherms
Molecules (glucose, glycerol) produced to lower freezing point
Antifreeze proteins allow ice to form in extracellular spaces, but not internally and prevent crystallisation (sharp edges)
what is shivering thermogenesis
Muscles move rapidly to generate heat but no movement
what is non shivering thermogenesis
Brown adipose tissue (fat) (brown because it has a lot of mito in it) is metabolised by the many mitochondria contained in this tissue
Mitochondria using uncoupling protein UCP1 to convert energy directly into heat rather than ATP
Proton gradient in mito is used by UCP1 and not ATP synthase (redirection)
when is non shivering thermogenesis used
organsims recovering from torpor, hibernation, and winter sleep
also newborns
