Thermogenesis

Thermogenesis or heat production is the production of heat by metabolic activity of living organisms. Heat is produced as an unavoidable by-product of metabolic processes such as energy metabolism, digestion and muscle activity in animals. There are also special metabolic pathways ( decoupled proton transport, substrate cycles ) in which chemical energy is only consumed to produce heat.

• 3.1 Notes and references

Thermogenesis in plants

Resulting in plants with normal breathing, in which, even under optimal conditions, 60 % of the energy in the form of heat is released not to a heating of the breathing organs, since the heat of the environment due to the open construction of the plant is discharged immediately into the atmosphere. However, some plants are able to be heated by means of certain organs thermogenesis.

The Cuckoo Pint ( Arum maculatum ) has the spadix an extension in which starch is stored before anthesis. Simultaneously with the opening of the flower bulb there is an increase of the respiration. The generally referred to as Calorigen hormonal signal was guttatum In Sauromatum identified as salicylic acid. When Arum in 12 hours about 75 % of the dry matter of the extension to be respired, respiratory intensity is at 200 to 400 ul CO2 · h-1 · mg dry weight -1, the 20 - to 40-fold of a mammalian brain. This is achieved by a greatly increased number and size of mitochondria, the enzymes of the citric acid cycle and respiratory chain are rising sharply. The electron transport takes place here, as in all thermogenic plants exclusively through the cyanidresistenten byway, the released energy is released directly as heat and is catalyzed by the alternative oxidase ( AOX).

In the Indian lotus (Nelumbo nucifera) thermogenesis takes place in the scar during receptivity. The temperature is maintained in the range between 30 and 35 ° C constant regardless of the ambient temperature. This is a very rare plant in the case of thermoregulation.

General thermogenesis occurs in plants mainly in the basal groups of angiosperms, but also in all cycads. As a function it is widely believed the attraction of pollinators, with increasingly fragrances are either distributed by the increase in temperature, or warm up the insects directly.

Thermogenesis in animals

Dozens of animals, especially mammals and birds as equally cold-blooded animals, have special mechanisms of thermoregulation. The heat generation can be classified into muscle and biochemical thermogenesis. In particular, for the additional heat production in brown adipose tissue, the term jitter-free thermogenesis (English non- shivering ) used in the literature often.

Muscular thermogenesis

Heat is generated in the skeletal muscle in

• Physical work
• Increase in muscle tone
• Shivering.

Since the efficiency of skeletal muscle rarely exceeds 20 %, physical work most of the energy used is converted into heat. Dissipation from the body without this leading to a corresponding heating. If the muscles increases in a cold environment involuntarily tense and so the muscle tone, heat is generated without causing mechanically useful work is done.

When shivering followed by a further increase in muscle tone through visible trembling of the muscles. The activated motor units to contract independently of each other; agonistic and antagonistic muscles alternately contract with normal movements, are now activated simultaneously. Shivering when the primary function of the muscular contractions of energy for heat generation; the so- recoverable heat output can reach four to five times the basal metabolic rate in humans with 320 to 400 watts. Genuine shivering as energetic heavy labor can be held by people maximum 2 hours.

Biochemical thermogenesis

Even at rest, heat is generated ( basal thermogenesis, basal metabolic rate ), any further increase in the metabolic rate leads to further, obligatory thermogenesis. If necessary, additional required heat is generated by the burning of fatty acids; in vertebrates, this occurs in the liver and - if available - in brown adipose tissue. The heat production in the brown adipose tissue, due to its isolation from the ATP synthesis is more effective. Production and activity of the uncoupling protein in brown adipose tissue thermo genius is induced by cold stimuli.

Bumblebees the genus Bombus a substrate cycle is found, the phosphofructokinase and fructose -1 ,6- bisphosphatase is based on the activity of the enzymes. Substrate cycles do not form a new metabolic products, but hydrolyze the cell's own energy carrier ATP to heat generation. The cycle described here allows the animals to reach the required temperature for the flying body to the idle state.

Postprandial thermogenesis

Also to digest ingested food, heat is released, as for adsorption, decomposition, transportation, conversion and storage of nutrients energy must be expended. In humans, about 10 % of the absorbed energy is in a mixed meal immediately ( taking place after the meal = ) in the form of postprandial thermogenesis "consumed" or implemented and enhanced for more hours of the basal metabolic rate. There are big differences depending on the food component: lipids with only 2 percent of its energy content is converted into heat, at 8 per cent glucose, proteins at 20 to 30 percent ethanol and 22 percent. In obese men found themselves in periods of high weight gain, however, only thermogenesis rates of 15 percent to 7 hours after ingestion of a pure protein meal.

Adaptation to changing environmental temperatures

A sudden drop in ambient temperatures shivering can be used as regulatory mechanism used immediately, while adjusting the biochemical thermogenesis requires a certain amount of time. From laboratory rats is known that prolonged lowering of the temperature, the first onset of violent shivering visibly decreases after a few days, the metabolic rate remains elevated. If in such a cold adapted to rats injected curare to prevent shivering, the metabolic rate of these animals is increased due to the continued acting thermoregulation. The term jitter-free thermogenesis for heat production, especially of brown adipose tissue derived from such observations.