adipose tissue

Connective tissue consisting mainly of fat cells, specialized to synthesize and contain large globules of fat, within a structural network of fibres. It is found mainly under the skin but also in deposits between the muscles, in the intestines and in their membrane folds, around the heart, and elsewhere. The fat stored in this tissue comes from dietary fats or is produced in the body. It acts as a fuel reserve for times of starvation or great exertion, helps conserve body heat, and forms pads between organs.

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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 contain a large lipid droplet surrounded by a ring 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 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.

Lineage

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.

References

External links

• - "Connective Tissue: unilocular (white) adipocytes "
• - "Connective Tissue: multilocular (brown) adipocytes"