A fibroblast is a type of cell that is responsible for making the extracellular matrix and collagen.

Together, this extracellular matrix and collagen form the structural framework of tissues in animals and plays an important role in tissue repair. Fibroblasts are the main connective tissue cells present in the body.
 

As well as being present as fibroblasts, these cells exist in an alternative state, as fibrocytes. Fibroblast is the term used to describe these cells when they are in an activated state. Fibrocyte refers to the less active state, when the cell is involved in tissue maintenance and metabolism. Some researchers use the term fibroblast for both cellular states but the term “blast” usually refers to a stem cell or a cell’s activated state.

The appearance of fibroblasts changes depending on their function and site of action. Fibroblasts taken from a particular location can “remember” their original location and function when transplanted to another location in the body.

Fibroblast origin

The primary function of fibroblasts is the maintenance of structural integrity within the connective tissue. They achieve this by secreting extracellular matrix precursors required for formation of the connective tissue and various fibres.

Fibroblasts are originally derived from primitive mesenchyme and therefore display the filament protein vimentin, which acts as a marker of mesodermal origin. In some cases, epithelial cells may also produce fibroblasts, a process which is referred to as epithelial–mesenchymal transition (EMT). Conversely, fibroblasts sometimes undergo mesenchymal–epithelial transition (MET) to produce epithelia, a process that is seen in development, tissue repair and tumor growth.