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| darmic |
 Posted: Sun Apr 27, 2008 4:10 am Post subject: Causes of hibernation |
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Forum Freshman
Joined: 03 Feb 2008
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Hello,
Does hibernation have anything to do with the rate of heat loss in bodies of different Surface Area-to-Volume ratios??
Thanks in advance.
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| biotoy |
| Posted: Sun Apr 27, 2008 8:45 am Post subject: |
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What is the surface hypothesis and what is the relationship between metabolic rate (heat loss) and an animal’s surface area?
The surface hypothesis, proposed by Max Rubner in 1883, states that the metabolic rate of birds and mammals that maintain a more or less constant body temperature should ultimately be proportional to their surface area. Since body size affects metabolic rate, and surface area is related to metabolic rate as well, there must be a correlation first between surface area and body mass. When animals of different size are compared to one another, their surface area varies to a .67 power of their body mass. This is due to the fact that different size animals within the same species follow the rule of isometry, or proportionality of shape regardless of the animal’s size. This concept does not hold for animals of different species and varying size. When this relationship is looked at, it can be found that the animal’s surface area varies to a .63 power of body mass. This is because when animals of different size and different species are compared to one another, they tend to follow the principle of allometry, which states that systematic changes in body proportions increases with a species size. When the basal metabolic rates of different size animals within the same species is plotted against body mass, the metabolic rate is proportional to the body mass raised to the .67 power, which is the same degree to which surface area and body mass are correlated among animals within the same species. But when basal metabolic rate in animals of different species are plotted against their body mass, the exponent relating the metabolic rate to the body mass is found to be .75. This is referred to as Kleiber’s law. The surface hypothesis holds true when metabolic rates are plotted against body size in animals belonging to the same species, but it does not hold true when metabolic rates are plotted versus body mass of animals within different species. When one is comparing different species, the metabolic rate cannot be determined simply on differences in body surface area. |
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| biotoy |
| Posted: Sun Apr 27, 2008 8:50 am Post subject: |
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Hibernation involves very specific reductions in metabolism (body heat specifically). To what extent are body heat and other metabolic processes affected during normal daily cycles?
Biological rhythms, specifically circadian rhythms, tend to be body temperature independent. An increase in Tb (body temperature) usually results in little or no corresponding increase in the circadian rhythms exhibited by the animal. A decrease in Tb is generally a derivative of these rhythms rather than vice versa. Thermogenesis and other indirect physiological mechanisms regulating Tb typically require considerable amounts of energy. Since Tb directly affects an animal’s metabolism, careful maintenance of that aspect of homeostasis illustrates the inherent relationship between circadian (and other biological) rhythms and energy metabolism.
Small animals typically exhibit larger circadian variation in Tb relative to the metabolic costs expended in daily regulation of biological functions. In some cases, rhythmic increases and decreases can be attributed to varying degrees of locomotor activity. Usually however, there is a distinct intrinsic rhythm in Tb that is independent of activity. This is evidenced in experimental settings where 1) an animal’s activity levels are controlled or corrected for and 2) where temperature fluctuations (in humans) have persisted for extended periods of complete bed rest. The most important and specific affectation of daily cycles as reflected by an animal’s metabolic rate occurs during slow wave sleep. A drop in hypothalamic temperature sensitivity and consequently Tb along with a reduction of respiratory and cardiovascular reflexes. |
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| paralith |
| Posted: Mon Apr 28, 2008 7:16 am Post subject: |
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Biotoy, if all that text was originally written by someone other than yourself, you need to list the source of the text.
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~Jean-Paul Sartre
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| biotoy |
| Posted: Mon Apr 28, 2008 7:31 am Post subject: |
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| i_feel_tiredsleepy |
| Posted: Mon Apr 28, 2008 7:48 am Post subject: |
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| I seem to remember that bears are capable of storing "brown fat" cells which are specialized adipocytes for heat production. They are found usually in neonatal mammals, but hibernating animals have evolved to retain brown fat cells for life. That is certainly a factor that makes hibernating possible. |
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| paralith |
| Posted: Mon Apr 28, 2008 8:05 am Post subject: |
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| biotoy wrote: |
| http://www.cartage.org.lb/en/themes/Sciences/Zoology/AnimalPhysiology/EnergeticsMetabolism/EnergeticsMetabolism.htm |
Thank you.
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Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
~Jean-Paul Sartre
Monkeys in Clothes - hosted by SFN blogs |
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| ExCre8ionist |
| Posted: Sat May 10, 2008 9:38 am Post subject: Hibernation in ground squirrels |
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