Warm-blooded - Heat Generation

Heat Generation

The "heat" comes from internal combustion, which we call metabolism. Metabolism basically refers to the chemical reactions cells use to break down glucose into water and carbon dioxide and in so doing generate ATP (adenosine triphosphate), a high-energy compound used to power other cellular processes.

All organisms metabolize food and other inputs, but some make better use of the output than others. Like all energy conversions metabolism is rather inefficient, and around 60% of the available energy is converted to heat rather than to ATP. In most organisms, this heat is simply lost to the environment. However, endothermic homeotherms (the animals generally characterized as "warm-blooded") both produce more heat and have better ways to retain and regulate it than other animals. They have a higher basal metabolic rate, and also a greater capacity to increase their metabolic rate when engaged in strenuous activity. They usually have well-developed insulation in order to retain body heat, fur in the case of mammals and feathers in birds. When this insulation is insufficient to maintain body temperature, they may resort to shivering--rapid muscle contractions that quickly use up ATP, thus stimulating cellular metabolism to replace it and consequently produce more heat. In hot environments, they generally use evaporative cooling to shed excess heat, either by sweating (some mammals) or panting (many mammals and all birds)-mechanisms not generally present in poikilotherms.