Lecture 12: Regulation of body temperature Flashcards

1
Q

for a constant body temperature…

A

heat loss must equal heat gain

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2
Q

homeostasis depends on

A

a constant body temperature

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3
Q

heat is lost/gained by ___ from warm to cold

A

diffusion

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4
Q

temperature affects ___ to maintain homeostasis

A

chemical reaction rate

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5
Q

when temperatures too low =

A
  • metabolism isn’t fast enough to maintain homeostasis
  • inadequate O2 supply
  • Freezing of cells
  • Reaction uncoupling
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6
Q

when temperatures too high =

A
  • proteins denature

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

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7
Q

4 types of heat exchange

A
  • radiation
  • conduction
  • convection
  • evaporation
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8
Q

radiation:

A

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

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9
Q

conduction:

A

direct transfer (with contact) (3%)

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10
Q

Convection =

A

air/fluid across body surface (15%)

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11
Q

Evaporation =

A

water from body surface (22%)

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12
Q

animals store heat in bodies by moderating heat transfer to

A

environment

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13
Q

heat storage + SA:V

A

larger abunals have proportionately lower heat flux

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14
Q

heat storage + temp gradient

A

– Between body and ext E

– Lower gradient = slower heat transfer

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15
Q

heat storage & specific heat conductance

A

– Insulation – reduces heat loss to ext E

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16
Q

poikilotherms =

A
  • ectotherms
  • body temp fluctuates with environment
  • heat derived from environment
17
Q

homeotherms

A
  • endotherms
  • constant Tb
  • heat derived from metabolism
18
Q

ectotherm Cost & benefits:

A

–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

19
Q

endotherm costs & benefits

A
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
20
Q

control of temperature in endotherms

A

hypothalamus detects + / - of thermoneutral zone.

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

21
Q

vasoconstriction:

A
  • 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
22
Q

shivering:

A

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)

23
Q

countercurrent heat exchangers

A

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

24
Q

gain heat: Brown fat =

A

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

25
gain heat = hormones
-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
26
gain heat: SA:V
– 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)
27
gain heat insulation
– 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
28
thermoregulation for losing heat"
``` Toohot? – Limit heat gain – increase heat loss • Vasodilation • Panting/sweating ```
29
Vasodilation:
• 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
30
lose heat : sweating/panting
• 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