The term ectotherm is used to describe cold-blooded animals or species in which the internal physiological sources of heat are relatively small or are of quite negligible importance in controlling body temperature. Such organisms rely on environmental heat sources to maintain their metabolic rates. All reptiles and amphibians are ectotherms. These organisms usually lie in environments where temperatures are practically constant. When they feel the need to warm up, they move to the areas with higher temperatures, and when they feel overheated they head to regions with low temperatures to stabilize their body temperature.
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Endotherms are animal species that maintain their body temperatures through internal processes and do not rely purely on their surroundings. The word endotherm is a combination of two Greek words - “endo” meaning within and “therme” meaning heat, signifying that these animals have internal heat. Nevertheless, even Endotherms have to make use of ambient heat at times.
All warm-blooded animals, mammals and birds, are endotherms, including human beings. A human body generates about two third of its heat through metabolism in the thorax, abdomen and brain. The human brain generates about 16 percent of the total heat produced by the human body.
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