Brown fat

Brown adipose tissue
Brown adipose tissue in a woman shown in a PET/CT exam
Details
Identifiers
Latin	textus adiposus fuscus
TH	H2.00.04.0.0004
FMA	20118
Anatomical terminology []

Brown adipose tissue (BAT) or brown fat makes up the adipose organ together with white adipose tissue (or white fat). BAT is found in almost all mammals.

Classification of brown fat refers to two distinct cell populations with similar functions. The first shares a common embryological origin with muscle cells, found in larger "classic" deposits. The second develops from white adipocytes that are stimulated by the sympathetic nervous system. These adipocytes are found interspersed in white adipose tissue and are also named 'beige' or 'brite' .

BAT is especially abundant in newborns and in hibernating mammals. It is also present and metabolically active in adult humans, but its prevalence decreases as humans age. Its primary function is thermoregulation. In addition to heat produced by shivering muscle, BAT produces heat by non-shivering thermogenesis.

In contrast to white adipocytes, which contain a single lipid droplet, brown adipocytes contain numerous smaller droplets and a much higher number of (iron-containing) , which gives BAT its brown appearance. Brown fat also contains more capillaries than white fat, to supply the tissue with oxygen and nutrients and distribute the produced heat throughout the body.

The presence of BAT in adult humans was discovered during FDG-PET scans to detect metastatic cancers. Using these scans and data from human autopsies, several BAT depots have been identified. In infants, BAT depots include, but are not limited to: interscapular, supraclavicular, suprarenal, pericardial, para-aortic and around the pancreas, kidney and trachea. These depots gradually get more white fat-like during adulthood. In adults, the depots that are most often detected in FDG-PET scans are the supraclavicular, paravertebral, mediastinal, para-aortic and suprarenal ones. It remains to be determined whether these depots are 'classical' BAT or beige/brite fat.