Endotherms use all the mechanisms used by ectotherms, but also generate and retain much metabolic heat. Since endotherms use metabolism to heat themselves, their metabolic rate might be expected to change with the temperature. Polar animals generally have a broader TNZ than tropical animals. The high end of the range, however, tends to be about 38 C for both polar and tropical animals. When the temperature rises above the TNZ, heart rate and blood flow increase to move heat to the body surface, where evaporative cooling takes it away.
Some animals sweat, some pant, some lick.
They are well-insulated with fur, fat, or tight feathers. On their poorly insulated parts, they have countercurrent heat exchangers, in which heat of warm, outflowing blood is transferred to cold, inflowing blood. They can swim faster than other fish. Their dark lateral muscles of a tuna are the warm muscles. Tuna blur the boundaries between warm and cold-blooded animals.