Thermal Relations post exam 1

Question 1

Thermal regulation in ectotherms

Answer 1

– 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

Question 2

Ectotherms in cold environments

Answer 2

– 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

Question 3

Preemptive ice crystal formation

Answer 3

– 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

Question 4

Freeze-tolerant animals

Answer 4

– 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

Question 5

Non-colligative cryoprotectants

Answer 5

– 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

Question 6

Mechanisms used by freeze-intolerant animals

Answer 6

– 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

Question 7

Antifreeze proteins

Answer 7

• 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

Question 8

How can poikilotherms prevent freezing?

Answer 8

• 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

Question 9

Note

Answer 9

study slides on page 6

Question 10

Thermoneutral zone

Answer 10

The range of temperatures (ambient temperature)
at which an animal does not have to actively
regulate its body temperature

Question 11

Lower Critical Zone

Answer 11

The lower temperature at which active
thermoregulation begins to maintain homeostasis

Question 12

Upper Critical Zone

Answer 12

The upper temperature at which active
thermoregulation begins to maintain homeostasis

Question 13

Mechanisms homeotherms use to
thermoregulate in thermal neutral zone

Answer 13

• 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?

Question 14

Metabolically inexpensive strategies used by
endotherms for temperature regulation

Answer 14

• 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

Question 15

Shivering thermogenesis

Answer 15

• Shivering thermogenesis
  – Chemical energy of muscle used for heat
  production
  – Groups of antagonistic muscles produce
  shivering
  – No physical work generated (energy used for
  heat)

Question 16

In a torpid state

Answer 16

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.

Question 17

Non-shivering thermogenesis

Answer 17

– 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

Question 18

Brown fat

Answer 18

is found most frequently in newborns,
hibernators and cold acclimated adults, especially
small species

Question 19

Countercurrent heat exchange
(heterothermy)

Answer 19

– 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

Question 20

non-insulated body parts

Answer 20

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

Question 21

Fur and blubber

Answer 21

– 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

Question 22

Pilomotor muscles of birds and mammals

Answer 22

can raise or lower feathers or hair to alter the
thickness of the insulating layer

Question 23

Thermoregulation above TNZ

Answer 23

• Behavior: avoidance
• Insulation
• Cycling of body
  temperature
• Hyperthermia-body temp warms too much, more effective in larger organisms

Question 24

Endotherms in warm environments

Answer 24

– 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

Question 25

Water availability

Answer 25

is important because without water, can’s use evaporative cooling (sweat)
measic-moist
zeanic-dry

Question 26

Active evaporative cooling

Answer 26

– 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)

Question 27

Heat windows

Answer 27

– Permit the loss of heat from the body surface
by radiation, convection or conduction
– Rabbits can dissipate excess heat through the
ears

Question 28

Carotid rate

Answer 28

– 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

Question 29

Thermostatic regulation of body temperature

Answer 29

– 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