endothermisk

Endothermisk, or endothermic, describes organisms that maintain a relatively constant internal body temperature largely through internal heat production rather than relying on environmental heat. In Swedish usage, endothermisk refers to animals that generate metabolic heat to stay warm, most notably birds and mammals, though some other groups show limited endothermic features such as regional heat production in certain fishes and sharks.

Mechanisms of endothermy include metabolic heat production from cellular respiration, with non-shivering thermogenesis often linked to brown adipose tissue in many mammals. Shivering can increase heat output when conditions are cold. Insulation from fur, feathers, or fat minimizes heat loss, and circulatory adjustments help retain or dissipate heat as needed. Birds and mammals also use behavioral adaptations, such as seeking shelter or sun exposure, to regulate temperature.

Thermoregulation is coordinated largely by the hypothalamus, which acts as the body’s thermostat. It compares core temperature with a set point and activates effectors such as vasoconstriction or vasodilation, sweating or panting, and behavioral changes to raise or lower heat. Fever is a controlled rise in body temperature during illness, reflecting immune system activity.

Endothermy entails substantial energetic costs, requiring high and consistent food intake to support a elevated metabolic rate. The concept of a thermoneutral zone describes the ambient range in which little extra energy is needed to maintain body temperature. Advantages of endothermy include sustained high activity and performance across environments, while drawbacks involve greater energy demands and vulnerability when resources are scarce.

Evolutionarily, endothermy has evolved independently in mammals and birds, with various hypotheses about its origins, including insulation, metabolism, and cardiovascular changes. Some species exhibit partial or regional endothermy, illustrating diversity in heat production strategies within the broader concept.