Lecture 12: Regulation of body temperature

Question 1

for a constant body temperature…

Answer 1

heat loss must equal heat gain

Question 2

homeostasis depends on

Answer 2

a constant body temperature

Question 3

heat is lost/gained by ___ from warm to cold

Answer 3

diffusion

Question 4

temperature affects ___ to maintain homeostasis

Answer 4

chemical reaction rate

Question 5

when temperatures too low =

Answer 5

• metabolism isn’t fast enough to maintain homeostasis
• inadequate O2 supply
• Freezing of cells
• Reaction uncoupling

Question 6

when temperatures too high =

Answer 6

• proteins denature

- inadequate O2 supply (affinity of Hb for O2 decreases with increased temperature)

Question 7

4 types of heat exchange

Answer 7

• radiation
• conduction
• convection
• evaporation

Question 8

radiation:

Answer 8

infrared wavelength without contact (60% heat loss); thermal

Question 9

conduction:

Answer 9

direct transfer (with contact) (3%)

Question 10

Convection =

Answer 10

air/fluid across body surface (15%)

Question 11

Evaporation =

Answer 11

water from body surface (22%)

Question 12

animals store heat in bodies by moderating heat transfer to

Answer 12

environment

Question 13

heat storage + SA:V

Answer 13

larger abunals have proportionately lower heat flux

Question 14

heat storage + temp gradient

Answer 14

– Between body and ext E

– Lower gradient = slower heat transfer

Question 15

heat storage & specific heat conductance

Answer 15

– Insulation – reduces heat loss to ext E

Question 16

poikilotherms =

Answer 16

• ectotherms
• body temp fluctuates with environment
• heat derived from environment

Question 17

homeotherms

Answer 17

• endotherms
• constant Tb
• heat derived from metabolism

Question 18

ectotherm Cost & benefits:

Answer 18

–Ectotherm benefits
– Metabolic rate of ectotherms is at least 5x slower than for endotherms
– Less energy = Less food = Less H2O
– Can devote larger proportion of energy budget to
reproduction
– Good colonizers of poor (and arid) E

–Ectotherm costs
– No nocturnal E niches (unless in tropical and summer temperate climates)
– Cannot sustain high activity bursts (run risk of O2 debt), so go to anaerobic = lactate accumulation = rapid fatigue
– Many are ambush predators but are susceptible to sustained predation by endotherms

Question 19

endotherm costs & benefits

Answer 19

Endotherm benefits
– Can sustain high activity bursts
– Nocturnal activity in all habitats
– Able to exploit colder E
– Forage widely and migrate over long distances
Endotherm costs
– the opposite of ectotherm benefits
– Require larger body sizes with relatively low SA:V ratios

Question 20

control of temperature in endotherms

Answer 20

hypothalamus detects + / - of thermoneutral zone.

-thermoregulatory réponses activated to revers direction of T change (negative feedback)

Question 21

vasoconstriction:

Answer 21

• diameter of superficial blood vessels decreases
• blood flow to skin decreases
• less heat lost to environment
• raises temperature of internal
• if heat loss continues –> shivering, countercurrent heat exchange

Question 22

shivering:

Answer 22

skeletal muscles consume ATP and generate heat (birds, mammals, insects)
– All energy released as heat because rapid movement of groups of antagonistic muscles (no useful work generated)

Question 23

countercurrent heat exchangers

Answer 23

hot artery flows by colder veins and exchanges heat so that cold blood doesn’t return to heart

Question 24

gain heat: Brown fat =

Answer 24

mammals;++mitochondriaand rich blood supply
– Mitochondria use different route that involves the protein thermogenin, that bypasses ATP production so all energy is heat
– New-borns, hibernators

Question 25

gain heat = hormones

Answer 25

-increase cellular metabolism (by product = heat )
-adrenalin
– Adrenal medulla releases, stimulate flight or
fight which means ++ HR (heart rate)
• Thyroxine
– Hypothalamus signal thyroid to release which elevates metabolic rate

Question 26

gain heat: SA:V

Answer 26

– Exchange limited by SA
– Decrease SA = rounder body shapes and shorter appendages
– Or increase size which decreased SA:V ratio
– E.g polar bears (compact ears and small tail)

Question 27

gain heat insulation

Answer 27

– Fur, hair, feathers
• Reduces effects of convection by trapping layer of warm air close to skin surface
• If air replaced by water, lose effect (why oil spills are bad)
• Eg. Polar bears – two fur layers – Blubber/fat
• Low metabolic activity but causes a low thermal conductivity of skin
• E.g. Polar bears – thick blubber layer

Question 28

thermoregulation for losing heat”

Answer 28

Toohot?
– Limit heat gain
– increase heat loss
• Vasodilation
• Panting/sweating

Question 29

Vasodilation:

Answer 29

• Heat exchange between internal E and skin mainly thru blood flow
• If upper critical limit reached, vessels to skin dilate
• Blood moved to skin and blood heat is lost to E (“flushed”)
• Ifheatcontinues–
– Panting/sweating
– Birds: no sweat glands; can gular flutter

Question 30

lose heat : sweating/panting

Answer 30

• H20 greater capacity for absorbing heat than air
• Release heat through evaporation (converting H20 liquid into vapour requires ++ heat)
• Last resort because
– H20 impt resource
– Active process requiring energy, triggered by adrenaline, which generates heat