Regulation of Body Temperature
Most animals have an upper limit of body temperature at which they can survive.In humans, for example, a body temperature of 41 degrees Celsius causes loss of protein function and breakdown of the nervous system, and a body temperature of 42 to 43 degrees Celsius is fatal. Birds, which have slightly higher resting body temperatures than mammals(approximately 40 to 41 degrees Celsius compared with 35 to 38 degrees Celsius for most mammals), cannot survive at body temperatures above 46 to 47 degrees Celsius. At environmental temperatures greater than 50 degrees Celsius, nearly all animals die. At the other end of the temperature spectrum, though, extreme cold is better tolerated. Fo example, Some animals can freeze and survive after thawing. Freezing/thawing is normally dangerous because ice crystals form inside cells and rupture membranes. However, many insects, such as the woolly caterpillar, a few species of amphibian such as the wood frog, and a very small number of reptiles such as the painted turtle, can block crystal formation in their cells. They do this by responding to ice on their skin surfaces with an enormous outpouring of glucose from the liver. The glucose stored in the liver enters the blood and the cells, lowering their freezing point so that the cells do not freeze solid. These animals can have 65 percent or more of their bodies completely frozen for long periods, only to thaw during warm periods without harmful effects.
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