Thermal Relations post exam 1 Flashcards
Thermal regulation in ectotherms
– Obtain heat from the external environment
– Do not produce enough metabolic heat
– Poorly insulated (metabolic heat quickly lost)
– High thermal conductance
– Have ‘preferred’ or ‘selected’ body
temperatures
– Regulate body temperature primarily through
behavioral mechanisms
Ectotherms in cold environments
– Ice crystal formation within cells is lethal
– Two broad strategies used by animals to
prevent intracellular ice formation:
* Freeze-tolerance- animals that can cope
with extensive freezing; ice crystals form
within the body
* Freeze-intolerance (freeze avoidance)- do
not form ice crystals within body, die very
quickly if any ice crystals begin to form
Preemptive ice crystal formation
– ECF contains an ice-nucleating agent
– Ice crystals form in the ECF but not in the ICF
– Solutes are excluded from the ice crystals and
become concentrated in the ECF
– Water is drawn out of the ICF (concentrates ICF
and lowers the freezing point of the ICF)
– Water in the ICF interacts with macromolecules
and remains unfrozen
– Some invertebrates have hydrophilic ice-
nucleating proteins
Freeze-tolerant animals
– Cryoprotectants- protect cells from injury
during drastic changes
* Colligative cryoprotectants
– Accumulate in high concentrations (0.2-2 M)
– Raise the osmotic concentration of the body
fluids (lowers the freezing point of ECF)
– Limited amount of total body is turned into
extracellular ice
Non-colligative cryoprotectants
– Occur at lower concentrations (<0.2 M)
– Usually membrane protectants
– Preserve subcellular structure from long-
term damage
– Trehalose and proline are common non-
colligative cryoprotectants
Mechanisms used by freeze-intolerant animals
– Supercooling: a liquid cooled below its freezing
point without solidifying
* Antarctic mites remain unfrozen at –200°C
– Antifreezes
* Glycerol- lowers the freezing point of the
ECF
Antifreeze proteins
- Present in polar marine fish
- Mainly glycoproteins
- Lowers the temperature at which ice
crystals begin to enlarge (prevents addition
of water molecules to the ice crystal lattice)
– Non-colligative- bind to forming ice crystals
How can poikilotherms prevent freezing?
- Animal body fluids freezing point –0.1 to -1.9°C
- Tissue can go below freezing point
(supercool) if slowly cool down; unstable - Supercooling point: temp where likely to
freeze - Supercooled solution will freeze if ice crystal
forms - If solution at 0 o has ice crystal, then
supercooling will be prevented
Note
study slides on page 6
Thermoneutral zone
The range of temperatures (ambient temperature)
at which an animal does not have to actively
regulate its body temperature
Lower Critical Zone
The lower temperature at which active
thermoregulation begins to maintain homeostasis
Upper Critical Zone
The upper temperature at which active
thermoregulation begins to maintain homeostasis
Mechanisms homeotherms use to
thermoregulate in thermal neutral zone
- Metabolic rate remains relatively constant
- Change insulation so that minimize difference
in Tb and Ta - Lab- you changed insulation with fat and fur
- What happens?
- How might a bird change insulation?
- What about behavioral mechanisms?
Metabolically inexpensive strategies used by
endotherms for temperature regulation
- Behavioral thermoregulation
– Change body shape or body orientation
relative to the sun or shade
– Huddling - Vasomotor response
– Selective vasoconstriction or vasodilation of
blood vessels to the periphery
Shivering thermogenesis
- Shivering thermogenesis
– Chemical energy of muscle used for heat
production
– Groups of antagonistic muscles produce
shivering
– No physical work generated (energy used for
heat)
In a torpid state
an animal’s metabolic rate drops allowing their body temperature to reflect the ambient temperature. Only can drop so much until the MR activates to keep a minimum temperature. Animals do it to save fat for migration.
Non-shivering thermogenesis
– Brown adipose tissue (brown fat)
* Rich in mitochondria and highly vascularized
* Capable of generating a large amount of heat
rapidly
* Present in bats, bears and human infants
* Oxidation takes place within adipose tissue itself
* Activated by the sympathetic nervous system or
thyroid hormone
Brown fat
is found most frequently in newborns,
hibernators and cold acclimated adults, especially
small species
Countercurrent heat exchange
(heterothermy)
– Present in flippers and flukes of cetaceans
– Flippers lack blubber and are poorly insulated
– Central outgoing artery (warm) surrounded by
incoming veins (cold) = ‘central rete’
– Arterial blood gives up heat to venous blood
non-insulated body parts
like the foot loses heat, warm blood enters and cold blood leaves, counter current warm blood heat colder blood when it passes by. Saves energy
Fur and blubber
– Vasoconstriction of
arterioles leading
to the skin lowers
conductance
(better insulation)
– Blubber is more
easily regulated
compared to fur
-gets more insulation from inside skin instead of coat blubber can be modified
Pilomotor muscles of birds and mammals
can raise or lower feathers or hair to alter the
thickness of the insulating layer
Thermoregulation above TNZ
- Behavior: avoidance
- Insulation
- Cycling of body
temperature - Hyperthermia-body temp warms too much, more effective in larger organisms
Endotherms in warm environments
– Limited heterothermy (e.g. camels)
* Animals with a small surface to mass ratio
eg. a camel tolerates elevation of its core
temperature by several degrees during the
hot day
* During the cool night it dissipates heat and
achieves a heat deficit by the next morning
* Daily cycling of body temperature
Water availability
is important because without water, can’s use evaporative cooling (sweat)
measic-moist
zeanic-dry
Active evaporative cooling
– Sweating- extrusion of water and salts
through pores onto surface of the skin;
activated by acetylcholine
– Panting- increase in the rate of breathing
through the mouth instead of the nose (oral
cavity absorbs less heat from exhaled air)
– Gular fluttering- birds rapidly vibrate their
gular area (floor of the mouth cavity) while
holding the mouth open
– Saliva spreading- some rodents and
marsupials spread saliva over their body
surfaces (relatively inefficient)
Heat windows
– Permit the loss of heat from the body surface
by radiation, convection or conduction
– Rabbits can dissipate excess heat through the
ears
Carotid rate
– Present in hooved animals (sheep, goats,
gazelles)
– Prevents the brain from overheating
– Countercurrent system uses cool venous blood
from the nasal airways to remove heat from the
arterial blood destined for the brain
Thermostatic regulation of body temperature
– Animals have multiple thermoreceptors located
in various regions of the body
– Both central (hypothalamus) and peripheral
thermoreceptors send signals to the brain
– The hypothalamus is the major
thermoregulatory integrative center or
“thermostat”
– Three subsets of neurons in the hypothalamus
are sensitive to changes in temperature
