Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat.
There are two types of adipose tissue, white adipose tissue (WAT) and brown adipose tissue (BAT), which are also known as white fat and brown fat, respectively, and comprise two types of fat cells.
White fat cells (unilocular cells)
White fat cells or monovacuolar cells contain a large lipid droplet surrounded by a layer of cytoplasm. The nucleus is flattened and located on the periphery. A typical fat cell is 0.1mm in diameter with some being twice that size and others half that size. The fat stored is in a semi-liquid state, and is composed primarily of triglycerides and cholesteryl ester. White fat cells secrete resistin, adiponectin, and leptin. An average adult has 30 billion fat cells with a weight of 30 lbs or 13.5 kg. If excess weight is gained as an adult, fat cells increase in size about fourfold before dividing and increasing the absolute number of fat cells present.
Brown fat cells (multilocular cells)
Brown fat cells or plurivacuolar cells are polygonal in shape. Unlike white fat cells, these cells have considerable cytoplasm, with lipid droplets scattered throughout. The nucleus is round, and, although eccentrically located, it is not in the periphery of the cell. The brown color comes from the large quantity of mitochondria. Brown fat, also known as "baby fat," is used to generate heat.
Although the lineage of adipocytes is still unclear, preadipocytes are undifferentiated fibroblasts that can be stimulated to form adipocytes.
Mesenchymal stem cells can differentiate into adipocytes, connective tissue, muscle or bone.
Areolar connective tissue is composed of adipocytes.
The term "lipoblast" is used to describe the precursor of the adult cell. The term "lipoblastoma" is used to describe a tumor of this cell type.
The number of fat cells stays constant in adulthood in lean and obese individuals, even after marked weight loss, indicating that the number of adipocytes is set during childhood and adolescence. Approximately 10% of fat cells are renewed annually at all adult ages and levels of body mass index.
- ↑ Pool, Robert (2001). Fat: fighting the obesity epidemic. Oxford [Oxfordshire]: Oxford University Press. ISBN 0-19-511853-7.
- ↑ Hong R, Choi DY, Do NY, Lim SC (July 2008). "Fine-needle aspiration cytology of a lipoblastoma: a case report". Diagn. Cytopathol. 36 (7): 508–11. doi:10.1002/dc.20826. PMID 18528880.
- ↑ "Dynamics of fat cell turnover in humans" Kirsty L. Spalding, et al. Nature 453 783-787, (2008)
- ↑ Nelson LR, Bulun SE (September 2001). "Estrogen production and action". J. Am. Acad. Dermatol. 45 (3 Suppl): S116–24. doi:10.1067/mjd.2001.117432. PMID 11511861.
- ↑ FERTILITY FACT > Female Risks By the American Society for Reproductive Medicine (ASRM). Retrieved on Jan 4, 2009
- - "Connective Tissue: unilocular (white) adipocytes "
- - "Connective Tissue: multilocular (brown) adipocytes"