thermoregulation - bio.classes.ucsc.edubio.classes.ucsc.edu/bio131/thometz website/18...
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Thermoregulation
Thermal Strategies
Animals must survive thermal extremes
- the highest and lowest TA in their niche
Animals must survive thermal change
Thermal Strategies
Many ecosystems exhibit spatial variation in
temperature:
Underground refuges buffered from thermal
extremes on the surface
Large bodies of water decrease in temp with
increasing depth
Daily cycles of cold and heat.
Thermal Strategies
Heat Exchange
The most important physiological
parameter in an animal’s thermal
physiology is body temperature (TB)
An animal’s thermal strategy serves to
control the transfer of energy between
animal and environment.
Metabolism = major source of thermal E
for many animals.
Other routes for thermal energy, into and
out of an animal:
◦ Conduction
◦ Convection
◦ Radiation
◦ Evaporation
Conduction: transfer of thermal E from
one region of an object or fluid to another
Convection: transfer of thermal energy
between an external fluid that is moving
Radiation: emission of electromagnetic
energy from an object.
Evaporation: loss of water molecules from
the surface of an object (absorbing thermal E)
Controlling Heat Fluxes
Thermal Energy (H)
Htotal = Hmetabolism + Hconduction +
Hconvection +Hradiation + Hevaporation
◦ If Htotal = 0 TB will remain constant
◦ If Htotal = + TB will increase
◦ If Htotal = - TB will decrease
Thermal Conduction
Heat is conducted from internal tissues, thru
other tissues and fluids, and into surroundings.
High thermal conductivity = heat sink
◦ Water has a higher thermal conductivity than air.
An animal will lose heat much faster in water
than in air due to interplay of conduction and
convection.
Convective Heat Loss
Body works to warm “boundary layer”
Strength of gradient between animal and
environment determines heat loss.
Heat lost to a moving fluid (air or water)
is convective heat loss
Radiant Energy
Sun = most important source of radiant heat:
Photons from the sun excite molecules in the
atmosphere, warming them by radiant heat.
Evaporation
Evaporative cooling:
◦ Fluid draws thermal energy from the body
surface as water molecules make transition
from liquid to vapor.
Magnitude of heat loss dependent upon
volume of water and heat of vaporization.
◦ Requires more energy to evaporate salty
sweat than pure water
Surface Area to Volume Ratio
Surface Area to Volume Ratio
Surface Area to Volume Ratio
Bergmann’s Rule:
◦ States that animals living in cold environments
tend to be larger than animals in warmer
environments
Allen’s Rule:
◦ States that animals in colder climates tend to
have shorter extremities than animals in
warmer climates.
Insulation
Internal and external insulation reduce
heat losses.
Fur and feathers:
◦ restricts movement of molecules between the
surface of the animal and the environment.
Blubber:
◦ lipid layer disrupts the flow of thermal energy
from the core to external surface of animal.
Insulation
External Insulation:
◦ Molecules of air in the insulation layer are
warmed by the animal and then trapped
within the insulation
External Insulation
External Insulation
Some species change thickness of
external insulation seasonally.
Thick coats are a thermoregulatory
burden in the warm season:
◦ Beneficial to shed fur in the spring
◦ Cost of rebuilding coat when temperatures
cool is much less than cost of trying to stay
cool in the warm season
Internal Insulation - Blubber Fur
Uncommon to be main
form of insulation for MMs
Compressible
Energetically expensive
Blubber
Common insulation
for marine mammals
Non-compressible
Energy store
Thermal Strategies
Poikilotherm:
◦ Animal with a variable TB
◦ Varies with environmental conditions
Homeotherm:
◦ Animal with a relatively constant TB
Distinction depends on both physiology
of animal and nature of environment.
Thermal Strategies
Ectotherm: environment determines TB
Endotherm: generates internal heat to maintain TB within a narrow range.
The terms ectotherm and endotherm distinguish animals by the physiological mechanisms that determine TB.
Homeothermy
Homeotherms maintain their CNS and internal organs at a more constant temperature.
Core temperature: temperature of deep internal regions.
Regional Endothermy
Many homeotherms experience some
sort of temperature variation.
Regional endothermy: keep core
temperature near-constant, while other
regions of the body (ex. extremities) can
experience temperatures much lower
than core.
Temporal Heterotherms
Many mammals and some
birds undergo dramatic,
prolonged changes in TB
Although their bodies cool,
considered homeotherms b/c
produce and maintain metabolic
heat to keep TB above TA
Regional Heterotherm
Regional heteroterm:
can retain heat in certain
regions of the body.
Heater organs: produce enough
heat near eyes and optic nerves to
improve visual clarity when diving
deep into cold waters
MARLIN
SWORDFISH
Thermotolerance
Animals have a characteristic degree of thermotolerance.
Ectotherms: changes in TA alter TB, directly changing rate of many biological processes.
◦ Preferred Temperatures
Endotherms respond to changes in TA by inducing regulatory responses.
◦ Thermal Neutral Zones
Thermal Neutral Zone
Environmental temperature (°C)
Meta
bolic
Rat
e
Lower critical
temperature
Upper critical
temperature
BMR
(Adapted from Eckert 2001)
Metabolic Regulation
Heat Production Active Heat
Dissipation
Thermal Windows
Thermal window: area of an animal’s
body that has the ability to radiate a
considerable amount of body heat relative
to other areas.
Extremities, areas with high SA:V ratios,
highly vascularized areas, may all serve as
thermal windows.
Thermal Windows
http://news.bbc.co.uk/2/hi/science/nature/8165895.stm
Counter Current Heat Exchange
Counter Current Heat Exchange
Shivering Thermogenesis
Bodily response to the early stages of hypothermia.
◦ Triggered by drop in core body temperature
◦ Primary motor center for shivering in hypothalamus
Smallest neurons recruited first, followed by the larger neurons.
◦ individual myofibers contract, but motor units are uncoordinated
Antifreeze Proteins (AFP)
The solutes in animal tissues reduce the
freezing point of water, but generally not lower than about -2°C.
Antifreeze Proteins - disrupt ice crystal
formation by binding to the surface of
small ice crystals to prevent their growth