Fibroblast, Fibrocyte, Macrophage

Abstract

In panels A and B, an active fibroblast and its inactive counterpart, referred to as fibrocyte, are on display, respectively. Fibroblasts constitute the main resident cells of the connective tissue. They synthesise and secrete both the components of the connective tissue ground substance and the precursor molecules of various types of collagen and elastic fibres. The secretory program of the fibroblasts determines the composition of the extracellular matrix and, as a consequence, provides the basis for the construction of a certain type of connective tissue. Fibroblasts are spindle-shaped and show all the characteristics of cells active in protein synthesis. In the karyoplasm, nucleoli are prominent. The long cytoplasmic extensions with multiple surface folds contain densely packed rough endoplasmic reticulum (ergastoplasm). In the Golgi apparatus, the secretory proteins are modified and, after completion, packaged into small vesicles or other post-Golgi carriers to be subsequently transported to the cell surfaces and exported via exocytosis.