Adipose tissue
The adipose tissue originates from the mesenchyma and is considered as a subtype of the connective tissue.
It is formed of adipose cells, also called adipocytes or fat cells. These cells may be found scattered singly within the connective tissue or either form clusters of diverse sizes, constituting the adipose tissue. In addition to adipocytes, adipose tissue also contains blood vessels, nerves, and smaller numbers of other resident and transient connective tissue cells.
The adipose cells of the adipose tissue 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 is difficult to observe under a light microscope in routine stained sections (for example stained with hematoxylin and eosin).
Adipocytes are characterized by the accumulation of lipids in their cytoplasm as different sized droplets. The lipid droplets are not surrounded by a membrane and are not considered as organelles but as cell inclusions.
The lipids are mostly triglycerides, also called neutral fats.
The number and size of adipocyte lipid droplets can vary considerably.
When adipose cells are developing, they contain large numbers of small lipid droplets in their cytoplasm. In adult adipose cells, the droplets can merge into a large droplet or remain as droplets.
Thus, two varieties of adipose tissue are recognized: unilocular and multilocular. Unilocular and multilocular adipose tissues have significant differences in morphology, function, and distribution in the body.