Fibroblast

Fibroblasts are the most common cells of connective tissue.

Fibroblasts and fibrocytes are two states of the same cells, the former being the activated state, the latter the less active state, concerned with maintenance. Currently, there is a tendency to call both forms fibroblasts.

Fibroblasts are morphologically heterogeneous with diverse appearances depending on their location and activity. 

Like other cells of connective tissue, fibroblasts are derived from primitive mesenchyme.

Fibroblasts have a branched cytoplasm surrounding an elliptical, speckled nucleus having one or two nucleoli. Active fibroblasts can be recognized by their abundant rough endoplasmic reticulum. Inactive fibroblasts, which are also called fibrocytes, are smaller and spindle shaped. They have a reduced rough endoplasmic reticulum. Although disjointed and scattered when they have to cover a large space, fibroblasts when crowded often locally align in parallel clusters.

The main function of fibroblasts is to maintain the structural integrity of connective tissues by continuously secreting precursors of the extracellular matrix. Fibroblasts secrete the precursors of all the components of the extracellular matrix, primarily the ground substance and a variety of fibres. The composition of the extracellular matrix determines the physical properties of connective tissues.