Termogenezis

Termogenezis, or thermogenesis, is the biological production of heat by living organisms. It accompanies energy metabolism and helps maintain core body temperature and metabolic homeostasis. Thermogenesis can be obligatory, arising from the basic energy cost of cellular activity, or facultative, activated by cold exposure or stress to generate additional heat.

In mammals, a major site of facultative thermogenesis is brown adipose tissue (BAT). BAT contains mitochondria that express uncoupling protein 1 (UCP1). When activated by sympathetic stimulation, UCP1 uncouples oxidative phosphorylation from ATP production, releasing energy as heat. Beige adipocytes are inducible cells within white adipose tissue that can acquire UCP1 and contribute to heat production. Shivering thermogenesis, another mechanism, is produced by rapid skeletal muscle contractions that convert chemical energy into heat.

Thermogenesis is regulated by the sympathetic nervous system and thyroid hormones. Cold exposure stimulates catecholamine release and activates thermogenic pathways, while thyroid hormones increase basal metabolic rate, amplifying heat production. Environmental temperature, nutrition, and physical activity can modulate the magnitude of thermogenesis.

In humans, brown adipose tissue is most abundant in newborns and decreases with age, though small deposits persist in many adults and can be recruited in response to prolonged cold. Thermogenesis has implications for energy balance, obesity, and metabolic health, and is a focus of research into metabolic regulation and potential therapies.

Some plants also exhibit thermogenesis during flowering, producing heat to volatilize odors and attract pollinators in certain species, such as Amorphophallus titanum. This plant-based thermogenesis is mechanistically distinct from animal heat production.