Transcript Thermoregulation - Stosich Science

Thermoregulation
SBI4U Biology
Homeothermy
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“Same
Temperature”
Endotherm
Mammals, Birds
Metabolically costly!
Large caloric intake
More habitat choice
Thermoregulation
mainly physiological
Poikilothermy
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“Colourful (Variable)
Temperature
Ectotherm
Reptiles, Amphibians
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Metabolically cheaper
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Lower caloric intake
Limits habitats
Thermoregulation
mainly behavioural
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Controlling Body Temperature
Comparing the two
Physiology of
Homeothermy
Hormones, such
as thyroxine
• Nervous control,
including
peripheral nerves
• Receptors in skin
& within body
• Hypothalamus is
coordinator of
thermoregulation,
as well as a
receptor
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Not so simple, is it? And it’s all automatic…
Shivering:
An autonomic
nervous response
• Rapid muscle
contractions
generate heat
• costs us some
energy, though, so
not a long term
solution.
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Goosebumps:
Erector pili
muscles try to
raise our hair
• Raised hair traps
air as a layer of
insulation, warmed
by body heat
• Great for furry
mammals, not so
much for the
‘Naked Ape’…
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Control Skin
blood flow:
Pre-capillary
Sphincter muscles
stop blood flow, to
avoid heat loss.
• Vasoconstriction
• If prolonged, the
muscles relax
(Vasodilation) to
prevent tissue
damage.
• Appendages most
affected: ears,
nose, feet, hands…
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Adaptations to
cold:
Behavioural
postures
• Shorter limbs &
extremities
• Thicker fur, fat…
• Hibernation:
long term solution
to save a LOT of
metabolic energy
• Seasonal
migrations, too.
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Losing Heat:
Radiate it out of
your skin –
vasodilation of
capillaries will
increase blood flow
& heat loss.
• Evaporate it off of
your skin – nerves
stimulate sweating
• Evaporate it off
your tongue – dogs
& birds pant.
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Dealing with
Heat:
Avoiding the energy
cost by estivation &
torpor
• Torpor is a sleeplike state, where
body temperatures
are allowed to
fluctuate more than
usual
• Birds, small
mammals, land snails,
toads.
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Adaptations
for Heat:
Long limbs &
extremities
• Turbinate bones
in nasal cavity are
numerous, thin, &
covered in moist
tissues for
evaporative heat
loss.
• Behavioural:
postures, being
nocturnal…
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Adaptations for
Heat:
“Rete Mirabile”: Latin
for “miraculous net”
• Arterial blood warms the
Venous blood in cold, and
bypasses the ‘net’
• In heat, blood freely
flows into the ‘net’, heat
lost.
• Mostly mammals
• Countercurrent Heat
Exchange
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Everyone’s a bit
different…
Like many other
homeostatic responses,
thermoregulation is also
influenced by:
• genetics
• acclimation
• However, a range of
tolerance exists;
exceeding it is harmful:
hypothermia &
hyperthermia kill!
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