Brown adipocyte : special connective tissue

Brown adipocyte :

Brown adipose tissue is present in humans during fetal life but diminishes during the first decade after birth. Brown adipose tissue makes up about 5% of the total body mass.

Microscopic features: Multilocular adipose tissue contains numerous fat droplets. Brown (multilocular) adipocytes are smaller in diameter (10–25 µm) than those of white adipose tissue.

Multilocular, spherical, round eccentric nucleus. The multilocular adipocyte contains numerous mitochondria, a small Golgi apparatus, and only small amounts of rER and sER. The mitochondria contain large amounts of cytochrome oxidase, which imparts the brown color to the cells.

Function: Brown adipose tissue is present in large amounts in the newborn, which  prevent  the extensive heat loss by heat production (thermogenesis) that results from the newborn’s high surface-to-mass ratio and avoid lethal hypothermia (a major risk of death for premature babies).

Distribution : It is located on the back, along the upper half of the spine, and toward the shoulders. In adult it is gradually decreases. At first decade of life it is situated in the cervical, axillary, paravertebral, mediastinal, sternal,and abdominal regions of the body.

It then disappears from most sites except for regions around the kidney, adrenal glands, large vessels (i.e., aorta), and regions of the neck (deep cervical and supraclavicular), regions of the back (interscapular and paravertebral), and thorax (mediastinum).

Metabolism: brown fat contain numerous mitochondria which are capable of uncoupling proton leakage and instead of producing adenosine triphosphate (ATP), they release heat, thus arousing the animal from hibernation.