Lecture 12: Regulation of body temperature Flashcards
for a constant body temperature…
heat loss must equal heat gain
homeostasis depends on
a constant body temperature
heat is lost/gained by ___ from warm to cold
diffusion
temperature affects ___ to maintain homeostasis
chemical reaction rate
when temperatures too low =
- metabolism isn’t fast enough to maintain homeostasis
- inadequate O2 supply
- Freezing of cells
- Reaction uncoupling
when temperatures too high =
- proteins denature
- inadequate O2 supply (affinity of Hb for O2 decreases with increased temperature)
4 types of heat exchange
- radiation
- conduction
- convection
- evaporation
radiation:
infrared wavelength without contact (60% heat loss); thermal
conduction:
direct transfer (with contact) (3%)
Convection =
air/fluid across body surface (15%)
Evaporation =
water from body surface (22%)
animals store heat in bodies by moderating heat transfer to
environment
heat storage + SA:V
larger abunals have proportionately lower heat flux
heat storage + temp gradient
– Between body and ext E
– Lower gradient = slower heat transfer
heat storage & specific heat conductance
– Insulation – reduces heat loss to ext E
poikilotherms =
- ectotherms
- body temp fluctuates with environment
- heat derived from environment
homeotherms
- endotherms
- constant Tb
- heat derived from metabolism
ectotherm Cost & benefits:
–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
endotherm costs & benefits
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
control of temperature in endotherms
hypothalamus detects + / - of thermoneutral zone.
-thermoregulatory réponses activated to revers direction of T change (negative feedback)
vasoconstriction:
- 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
shivering:
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)
countercurrent heat exchangers
hot artery flows by colder veins and exchanges heat so that cold blood doesn’t return to heart
gain heat: Brown fat =
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
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
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)
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
thermoregulation for losing heat”
Toohot? – Limit heat gain – increase heat loss • Vasodilation • Panting/sweating
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
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
