Temperature 3

Question 1

endothermy basics

Answer 1

• delicate balance of metabolic rate Mo2
• allows internal regulation of Tb
• has zone of thermoneutrality

Question 2

metabolic heat and regulating Tb

Answer 2

• Tb regulated within 1C, and usually >Ta
• (Tb 32-43C in most vert)
• Heat is produced as waste of metabolism
• Mo2 therefore must be 10 fold higher than ectotherms
• must have insulation to prevent heat loss to keep Tb>Ta

Question 3

HEATmetabolism=

Answer 3

-conduction+H-convection(together are usually minimized via insulation, tho variable between aquatic vs terrestrial)+radiation+evaporation (regulated for thermoregulation)

Question 4

limitations of thermoregulation

Answer 4

near 0C and >40C regulation becomes difficult and hypo/hyperthermia occurs

Question 5

metabolic responses to extreme Ta

Answer 5

-thermogenesis at low temp and active cooling at high temp, both costing higher metabolic rate

Question 6

thermoneutral zone

Answer 6

• range of Ta where animal maintains Tb without changing basal metabolic rate
• Tb maintained via seasonal insulation like blubber, fur, or feathers, and behaviour like huddling and shelter

Question 7

anatomical solutions to reduce heat loss: insulation

Answer 7

1. minimizes surface area to volume (ie seals, whales, penguins)
2. external insulation stabilizes air boundary layer
3. Internal insulation: adipose/fat tissue increases conduction distance
   - min. SA:Vol, and increased conduction distance via external/internal insulation minimizes heat conduction and radiation

Question 8

anatomical external insulation

Answer 8

• stabilizes air boundary layer, even in water, by increasing conduction distance
• ie. hair, fur, feathers
• seasonal variations in thickness

Question 9

physiological solutions to retain heat

Answer 9

1. cool extremeties via vasoconstrictions and contercurrent exchange systems
2. increased skin blood flow and evaporation
3. ‘cool heads’

Question 10

cool extremities/regional heterothermy

Answer 10

• reduce peripheral temperature to keep up core temperature of vital organs via:
  a) vasoconstriction in skin, increasing conduction distance
  b) countercurrent exchange so arterial blood conducts heat to cooled venous blood, returning some heat to the core

Question 11

active cooling: increased skin blood flow

Answer 11

• ANS-mediated vasodilation response
• increased peripheral temperature
• reduced insulation
• more radiation/conduction
• pigmentation to increase light reflection

Question 12

active cooling: increased evaporation

Answer 12

• sweating: hypothalamic control through symp nerves
• NaCl loss too
• acts as an acclimation to heat
• arterioles dilate and AV shunt constricts, forcing blood to move through skin for heat to convect out
• rapid shallow breating (panting) helps cool blood of moist respiratory membranes; no NaCl loss, requires skeletal muscle work

Question 13

Cool heads

Answer 13

• found in savannah mammals: route carotid artery blood flow past nasal passages before blood reaches brain via nasal breathing (ie. reindeer or camels)
• moving air through nasal passage cools blood as it goes to the grain, or move air through mouth to keep blood warm in low Ta

Question 14

Mechanisms for thermogenesis: increasing metabolic rate

Answer 14

1. increased cell membrane ionic leakiness
2. increased skeletal muscle activity
3. shivering thermogenesis
4. non-shivering thermogenesis

Question 15

mech for thermogenesis/increasing metabolic rate: cell membrane ionic leakiness

Answer 15

• Na/K-ATPase has to work harder to maintain membrane potential
• being able to increase leakiness is one of the main differences between endotherms and ectortherms, as it allows thermogenesis

Question 16

mech for thermogenesis: increased skeletal muscle activity

Answer 16

• more muscle activity means more METABOLIC WASTE HEAT

- creates increased convection, requires more food though due to greater Mo2, but also allows more movement for foraging

Question 17

shivering thermogenesis

Answer 17

futile energy cycling of involuntary muscle movement

• ANS, uncoordinated skeletal muscle contractions
• uses ATP without generating locomotion
• all birds and mammals use for short intense warming
• can cause muscle fatigue though, leave one open to predation

Question 18

non-shivering thermogenesis

Answer 18

• futile energy cycling in well-vascularised brown fat

- brown adipocytes=high mitochondrial content and express THERMOGENIN

Question 19

thermogenin

Answer 19

acts as proton ionophore in mitochondrial membrane

• uncouples electron transport from ATP production; this causes mito resp to increase without increasing ATP yield
• used by small mammals (<10 kg) and neonates

Question 20

thermoregulatory central control system

Answer 20

• afferent neurons sense temp (=sensory input)
• hypothalamic (CNS) centre detects Tb and integrates with periphery
• efferent discharge leads generate humoral and/or ANS responses(=effectors

Question 21

thermoregulatory peripheral system

Answer 21

-heat retention/gain effector systems=increase Mo2 and insulation
-behaviour
heat loss effector systems: reduce insulation, increase radiation, conduction, and evaporation