Endotherme

Endotherm is an organism that maintains a relatively constant internal body temperature largely through internal heat production. The term contrasts with ectotherms, whose body temperature is largely determined by ambient conditions. In biology, endothermy is seen mainly in birds and mammals, though some fishes exhibit regional endothermy.

Endothermy relies on metabolic heat production to raise body temperature above surrounding conditions. Mechanisms include non-shivering thermogenesis, shivering, and insulation from fat or fur or feathers. Birds and mammals regulate heat via the hypothalamus and cardiovascular adjustments, including changes in blood flow and heat exchange between body parts. Brown adipose tissue in many mammals contributes to rapid heat generation in cold conditions. Behavioral adjustments, such as seeking shelter or altering activity, complement physiological control.

Most endotherms are homeothermic, keeping core temperatures within a narrow range, though some species show seasonal or daily variation (torpor or hibernation). The fossil record indicates endothermy evolved independently in different lineages, notably in the ancestors of mammals and birds; in some fishes, such as tunas and certain lamnid sharks, regional endothermy raises the temperature of specific tissues, aiding muscle performance in cold waters.

Energetically, endothermy supports sustained activity and wide geographic distribution, but comes with high energy requirements and reliance on plentiful food.

In summary, endothermy is a physiological strategy characterized by internal heat production to maintain relatively stable body temperature, enabling activity across diverse environments and climates.