BIOL10004 Lecture Notes - Cellular Respiration, Headache, Torpor
Lecture 16 – Thermoregulation
Wednesday, 25 April 2018
Why Thermoregulate?
Human Body
• Good at internally regulating body temperature
Importance of Thermoregulation
• Biochemical reactions are temperature sensitive – there’s a tep ido i hih e aitai iohe reatios
o Through evolution body reactions have evolved for an optimum temp
o Body temp too low: metabolism slows (not fast enough to support life, biochemical pathways disrupted), body
functions disrupted
o Body temp too high: enzyme function destroyed, proteins denature
Optimum body temperature varies among groups
• -2C (polar fish) – live in saltwater ad of salts it does’t freeze at 0C instead lower temperature
o Fish swim around in -2C – have salts in bloodstream to stop them freezing at this temp (enzymes optimised for
-2C)
• 80C (animals at thermal vents) – eg. crabs near geothermal vent
• 0C to 37C (most animals)
Human Body Temperature
Normal Body Temperature
• 36.5 – 37.5C
Too Hot
• 38C – sweating, feeling very uncomfortable
• 40C – starts to be life-threatening
• 41C – medical emergency – fainting, vomiting,
severe headache, dizziness, confusion,
hallucinations, delirium and drowsiness can occur
• 43C – usually death
Too Cold
• 36C – mild to moderate shivering (to moderate
heat)
• 32C – medical emergency – hallucinations,
delirium, complete confusion, extreme
sleepiness that is progressively becoming
comatose (biochem pathways not able to
operate fast enough to feel normal)
• 31C – comatose, very rarely conscious. No or
slight reflexes. Very shallow breathing and slow
heart rate – if at this temp or lower for long
period death
• 26C – usually death
What Determines Body Temperature?
Metabolism
• Metabolism generates heat (as a waste product or end product)
o All biochemical pathways incl. cellular respiration
• Increase in body temp increases metabolic rate – process act faster
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Heat Exchange (4 methods)
• Heat always moves from an area of high heat to low heat
• Conduction – direct contact etee a aial’s ody ad aother surfae (heat exchange b/w us + environ)
• Convection – cooler air/water (currents) movement removes heat from body surface
o Often faster because air and water currents increase heat loss
• Evaporation – liquid cooling occurs when water (eg. from sweat or respiratory surfaces – breathing out on cold
day produces mist) evaporates
• Radiation – thermal (infra-red) radiation from sun to animal (radiant heat), or from animal to surroundings
Cold-blooded vs War-blooded
Inaccurate terms (as can transfer from one form to another)
• Cold-blooded animals are only cold in an environment
o A askig reptile old looded ay hae a ody tep higher tha a aal’s
• Warm-blooded animals hibernate – body temp drops very low
Other terms
• Poikilothermic – body temperature varies, fluctuates with environmental temp (replaces cold blooded – altho some
reptiles can manage their temps even in changing environments)
• Homeothermic – constant body temperature, regulated independently of environment
• But what about hibernating mammals?
Ectothermic and Endothermic (Most Useful Terms)
Ectothermic and Endothermic
• Distinguishes where heat is generated
Ectothermic
• Body temperature determined solely by the environment (most animals)
• Metabolic heat is negligible
• As ambient temp increases – body temp increases
Endothermic
• Majority of body heat obtained internally – from production of metabolic
heat
• Birds, mammals, a few fish (eg. tuna), a few reptiles, humans, some
insects (eg. honeybees)
Ectotherms
Animals that are dependent on external sources of body heat
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Ectotherms
• Most animals are ectotherms: low metabolic heat production (eg. Lizards, turtles, etc)
• Many live in environments with little temperature fluctuation (eg. Aquatic)/ more likely to
find in these environments
• May have long periods innactive
o Eg. If too cold – spend time to warm up because of low metabolic rate
• Ca’t otrol ody teperature physiologially do’t hae sae theroregulatory systes
as ectotherms) but can regulate temperature behaviourally
Life as an
Ectotherm
• Find places and times where temperature is OK; avoid places and times where undesirable
temps are reached
• Can adjust behaviour often in order to keep body temperature relatively consistent
o Eg. Lizard on branches airing itself (exposing SA to air)
Behavioural
Temperature
Adjustment
• Move to warmer or cooler areas (rocks, burrows, etc)
• Change coloration (darker colors absorb more heat)
• Change SA exposed to heat source/sink (eg. Sit on twigs to get breeze or lie on something
warm)
o Basking – many animals particularly reptiles (eg. Fish, lizards) & in early morning to
raise body temp; use radiant heat to warm up by sitting in area of warmth
• Evaporative cooling (eg. panting)
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