Brown adipose tissue

The brown adipose tissue or plurivakuoläre is a special form of the adipose tissue, which cells are capable of producing fatty acids by the oxidation of heat (thermogenesis ). This is done in a number of mitochondria, which are responsible for the yellow- brownish color of the fabric. Biochemically, the fatty acid oxidation is uncoupled from the adenosine triphosphate synthesis, so that the released energy is converted into heat by Thermogenin.

Occurrence

Brown adipose tissue is found in all newborn mammals, except in pigs. Newborns are more vulnerable to hypothermia because they, due to the smaller size (larger body surface area compared to volume) lose more heat and the mechanisms of thermoregulation (eg insulating white fat and shivering ) are not yet fully formed. In the human infant is found brown adipose tissue, especially in the neck and chest.

For adults, it was assumed that they would have no active brown fat cells more. Due to recent studies, it was found that could have "at least a few tens of percent " of adults over active brown fat cells. In humans, the activity of brown fat cells is strongly induced by cold stimulation and stimulated by the sympathetic nervous system.

Especially rodents do not have in the adult state greater amounts brown adipose tissue and white can transform into brown fat and so survive cold spells good means of catecholamines when needed. In hibernating animals also find larger amounts of brown fat, which is used for rapid heating of the animal in the awakenings.

In some birds appear histologically similar tissue which, unfortunately, no Thermogenin and do not serve the thermogenesis. However, some birds can generate heat in the skeletal muscles via biochemically similar mechanisms.

Histology

The cells of brown adipose tissue are generally less than in white adipose tissue, and have many small lipid droplets. They are therefore, in contrast to the cells of the white adipose tissue univacuolar called plurivakuolär. In addition, they are characterized by particularly rich in mitochondria, which are responsible because of their content of cytochromes also for the brown color.

Biochemistry

The existing brown fat tissue in the inner mitochondrial membrane protein Thermogenin serves as a decoupler by transporting as uniporter protons across the membrane. A result, the proton gradient built up by β - oxidation and respiratory chain is broken and the energy stored therein is converted into heat (thermogenesis ). In addition, brown fat has a particularly high concentration of glycerokinase, so that this can be phosphorylated liberated glycerol in fat loss and also converted metabolically.

Regulation

The thermogenesis in brown adipose tissue is activated by the hormone norepinephrine, which activates a G- protein-coupled β - receptor adenylate cyclase. The cAMP in turn formed activated protein kinase A, which initiates the fat loss on phosphorylation of lipases. In addition, brown adipose tissue is innervated by sympathetic.

Activity and formation of brown adipose tissue is by PGC -1alpha (peroxisome proliferator - activated receptor -gamma coactivator ) increased, which in turn is distributed by strong cold stimulus.

There is evidence that the relationship between brown and white adipose tissue of the micro - RNA 155 is affected.

Swell

• Georg Löffler, Petro E. Petrides, Peter C. Heinrich: Biochemistry and Pathobiochemistry. 8 edition. Springer, Heidelberg 2006, ISBN 978-3540326809.
• Werner A. Müller: Animal and Human Physiology. Springer, Heidelberg 1998, ISBN 3-540-63313-8.