Thermogenesis is the process of
heatIn physics and thermodynamics, heat is the process of energy transfer from one body or system due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body....
production in organisms. It occurs mostly in
warm-bloodedIn biology, a warm-blooded animal species is one whose members maintain thermal homeostasis; that is, they keep their body temperature at a roughly constant level, regardless of the ambient temperature. This involves the ability to cool down or produce more body heat. Warm-blooded animals mainly...
animals, but a few species of
thermogenic plantsThermogenic plants have the ability to raise their temperature above that of the surrounding air. Heat is generated in the mitochondria, as a secondary process of cellular respiration called thermogenesis...
exist.
Types
Depending on whether they are initiated through locomotion and intentional movement of the
muscleMuscle is the contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s, thermogenic methods can be classified as one of the following:
- Exercise-associated thermogenesis (EAT)
- Non-exercise-associated thermogenesis (NEAT)
- Diet- induced thermogenesis (DIT)
Shivering
One method to raise temperature is through
shiveringShivering is a bodily function in response to early hypothermia in warm-blooded animals. When the core body temperature drops, the shivering reflex is triggered. Muscle groups around the vital organs begin to shake in small movements in an attempt to create warmth by expending energy...
. The heat results from
frictionFriction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact. It is usually subdivided into several varieties:...
between muscle elements (the same as during exertion), but no
mechanical workIn physics, mechanical work is the amount of energy transferred by a force acting through a distance. Like energy, it is a scalar quantity, with SI units of joules...
is produced because opposing (
antagonisticAn "antagonist" is a classification used to describe a muscle that acts in opposition to the specific movement generated by the agonist and is responsible for returning a limb to its initial position.-Antagonistic pairs:...
) muscle pairs are activated at the same time.
Non-shivering thermogenesis
Non-shivering thermogenesis usually occurs in
brown adipose tissueBrown adipose tissue or brown fat is one of two types of fat or adipose tissue found in mammals. It is especially abundant in newborns and in hibernating mammals. Its primary function is to generate body heat in animals or newborns that do not shiver...
(brown fat) that is present in human infants and hibernating
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
s. It is a process whereby substances such as free fatty acids (derived from triacylglycerols) remove purine (ADP, GDP and others) inhibition of
thermogeninThermogenin is an uncoupling protein found in the mitochondria of brown adipose tissue . It is used to generate heat by non-shivering thermogenesis...
(
uncoupling proteinAn uncoupling protein is a mitochondrial inner membrane protein that can dissipate the proton gradient before it can be used to provide the energy for oxidative phosphorylation.There are five types known in mammals:* UCP1, also known as thermogenin* UCP2...
-1), which causes an influx of H+ into the matrix of the mitochondria and bypasses the
ATP synthaseAn ATP synthase is a general term for an enzyme that can synthesize adenosine triphosphate from adenosine diphosphate and inorganic phosphate by using some form of energy...
channel. This uncouples
oxidative phosphorylationOxidative phosphorylation is a metabolic pathway that uses energy released by the oxidation of nutrients to produce adenosine triphosphate . Although the many forms of life on earth use a range of different nutrients, almost all carry out oxidative phosphorylation to produce ATP, the molecule that...
, and the energy from the proton motive force is dissipated as
heatIn physics and thermodynamics, heat is the process of energy transfer from one body or system due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body....
rather than producing ATP from ADP.
The low demands of thermogenesis mean that free fatty acids draw, for the most part, on
lipolysisLipolysis is the breakdown of fat stored in fat cells. During this process, free fatty acids are released into the bloodstream and circulate throughout the body. Ketones are produced, and are found in large quantities in ketosis...
as the method of energy production.
Artificial thermogenesis
Thermogenesis can also be achieved by artificial means. It is becoming common for people to use thermogenic substances to help control fluctuation in weight. The process works by increasing the body's metabolism, thereby increasing its core temperature.
ThermogenicsThermogenics are dietary supplements used to stimulate weight loss. Thermogenics increase the body's consumption of energy , generating heat, by decoupling oxidative phosphorylation, requiring the body to burn more fuel to maintain temperature homeostasis. Thermogens do not stimulate fat metabolism...
are commonly made up of
ephedraEphedra, from the plant Ephedra sinica, has been used as a herbal remedy in traditional Chinese medicine for 5,000 years for the treatment of asthma and hay fever, as well as for the common cold. Known in Chinese as ma huang , ephedra is a stimulant which constricts blood vessels and increases...
,
bitter orangeThe name "bitter orange", also known as Seville orange, sour orange, bigarade orange, and marmalade orange,refers to a citrus tree and its fruit. Many varieties of bitter oranges are used for their essential oil, which is used in perfume and as a flavoring...
,
capsicumCapsicum is a genus of plants from the nightshade family native to the Americas, where it was cultivated for thousands of years by the people of the tropical Americas, and is now cultivated worldwide. Some of the members of Capsicum are used as spices, vegetables, and medicines...
,
gingerGinger is a tuber which is consumed whole as a delicacy, medicine, or spice. It is the rhizome of the plant Zingiber officinale....
, and
caffeineCaffeine is a bitter, white crystalline xanthine alkaloid that is a psychoactive stimulant drug. Caffeine was discovered by a German chemist, Friedrich Ferdinand Runge, in 1819. He coined the term kaffein, a chemical compound in coffee, which in English became caffeine...
.
Although
bodybuildingBodybuilding is a form of body modification involving intensive muscle hypertrophy; an individual who engages in this activity is referred to as a bodybuilder. In competitive bodybuilding, bodybuilders display their physiques to a panel of judges, who assign points based on their appearance...
formulations comprise the most common use of
thermogenicsThermogenics are dietary supplements used to stimulate weight loss. Thermogenics increase the body's consumption of energy , generating heat, by decoupling oxidative phosphorylation, requiring the body to burn more fuel to maintain temperature homeostasis. Thermogens do not stimulate fat metabolism...
, the drugs are entering the mainstream
dietingDieting is the practice of ingesting food in a regulated fashion to achieve or maintain a controlled weight. In most cases the goal is weight loss in those who are overweight or obese, but some athletes aspire to gain weight...
industry.