What mechanisms do warm-blooded
animals have for generating heat that
cold-blooded animals do not?
By Stella Angeli
Background taken from: http://userwww.sfsu.edu/~infoarts/cdmain/Tele/competency/elephant.jpg, http://farm4.static.flickr.com/3001/2631251051_5d36b95788.jpg?v=0
Warm-blooded and cold-blooded
animals
• Warm-blooded animals keep their body temperature at a constant level in
environmental changes by homeostatic mechanisms
o Mammals
o Birds
• Cold-blooded animals have their body temperature regulated by
interaction with the environment
o
o
o
o
o
Reptiles
Insects
Arachnids
Amphibians
Fish
Pictures taken from:http://coolcosmos.ipac.caltech.edu/image_galleries/ir_zoo/coldwarm.html, http://news.softpedia.com/images/news2/Cold-Blooded-Animals-HaveLarger-Offspring-in-Colder-Climate-2.jpg
Mechanisms for generating heat in
warm-blooded animals
• Larger number of mitochondria per cell
– Able to generate heat by increasing the rate at which they burn fats
and sugar
– Greater quantity of food in order to replace the fat and sugar
reserves
Background taken from:http://www.jigcardgallery.com/JigCard/icaPuzStore/Mammals2Part1.jpg
Picture taken from:http://www.disaboom.com/photos/storage/1000.29381.44443.MitochondriaSMALL2.jpg
Mechanisms for generating heat cont.
• Blood vessels in lower legs-heat exchangers (e.g. birds)
-Veins are close to arteries, extract heat from them
- Causes friction that produces heat
Heat is spread in the body and escapes through the skin
Picture taken from:http://openlearn.open.ac.uk/file.php/2314/S204_1_010i.jpg
Mechanisms for generating heat cont.
• Vasoconstriction
-Blood vessels close to the skin surface
become constricted
-Smaller surface area for heat to be lost
Minimal heat loss occours
• Shivering
-Muscle contraction around vital organs
-Cell respiration
Heat is produced by using energy
Pictures taken from:
http://www.biosbcc.net/doohan/sample/images/CO%20and%20MAP/VasTone.jpg,http://www.illustrationsof.com/images/clipart/xsmall2/2414_shivering_polar_bear_tryin
g_to_warm_up_beside_a_campfire.jpg
Mechanisms for generating heat cont.
• Insulation
-Adipose tissue(marine mammals):
 forms a thick layer of blubber
Thermal insulation
-Feathers and fur( birds, mammals):
 trap a layer of air next to the skin
Heat flow is reduced between the animal’s skin and the outside
Each feather has an individual muscle that allows it to be lifted away from the body
regulation of heat loss by changing the thickness of the air layer trapped among the
feathers
Fur contains hair close to the skin underneath thicker and larger surface hairs
longer hairs – better insulation
Pictures are taken from:
http://marinebio.org/upload/_04/Hydrurga_leptonyx8.jpg,http://www.cartage.org.lb/en/themes/Sciences/Zoology/Biologicaldiverstity/AnimalsIII/featherstruct.gif
Cold-Blooded animals
• Mechanisms for generating heat
-Snakes and Lizards sunning themselves on rocks.
-Fish changing depths in the water column to find a suitable temperature.
-Desert animals burrowing beneath the sand during the day.
-Insects warm their flight muscles by vibrating them in place.
Pictures taken from: http://curiousanimals.net/wp-content/uploads/2007/06/632604567-b5ba885b80-m-small.jpg, http://www.vegsoc.org/fish/images/single-fish.jpg
Summary
• Warm-blooded animals generate heat by:
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Having larger number of mitochondria per cell
Blood vessels in lower legs
Vasoconstriction
Shivering
Insulation (adipose tissue, feathers and fur)
• Cold-blooded animals have different mechanisms for
generating heat (sunning on rocks, burrow under the sand,
muscle vibration etc.)
References
Articles
• Anissimov M., Wise GEEK , What is the Difference Between Warm-Blooded
and Cold-Blooded Animals?, 2003-2009
• Watanabe M., Bioscience, Generating Heat: New Twists in the Evolution of
Endothermy,2005.55(6):470-475
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WebPages
http://en.wikipedia.org/wiki/Warm-blooded
http://en.wikipedia.org/wiki/Cold-blooded
http://openlearn.open.ac.uk/
http://en.wikipedia.org/wiki/Shivering
http://www.compulink.co.uk/~argus/Dreambio/homeostasis/ectotherms%
20and%20endotherms.htm
http://coolcosmos.ipac.caltech.edu/image_galleries/ir_zoo/coldwarm.html