The adipose tissue originates from mesenchymaL cells and is considered a subtype of the connective tissue.
The main cells of this tissue are the adipose cells, also called adipocytes or fat cells. They may be found scattered singly within the connective tissue or organized as clusters of diverse sizes. In addition to adipocytes, the adipose tissue also contains blood vessels, nerves and a small number of other resident and transient connective tissue cells.
The adipose cells are separated from each other by a small amount of extracellular matrix. This matrix consists largely of a network of thin reticular fibers formed primarily by type III collagen and usually not seen with a light microscope in routine stained sections.
Adipocytes are characterized by the presence of many lipid droplets in their cytoplasm. They droplets are not surrounded by a membrane and therefore not considered as organelles but as cell inclusions. Most of the droplet content are triglycerides (neutral fats).
The number and size of lipid droplets per adipocyte can vary considerably.
Large numbers of small lipid droplets are found as adipose cells are developing. As the cells mature, the droplets merge into one large droplet or, depending on the type of adipose tissue, remain as multiple droplets.
Thus, two varieties of adipose tissue are recognized: unilocular and multilocular adipose tissue. They show significant differences in their morphology, functions, and distribution in the body.
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