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Fibroblasts are specialized cells in connective tissue that synthesize and remodel the extracellular matrix, providing structural support to tissues. They are commonly spindle-shaped with elongated nuclei and are found throughout the interstitial spaces of many organs, including skin, tendons, and viscera. In adults they arise mainly from mesenchymal cells and can be activated by injury, inflammation, or mechanical cues.

The primary functions of fibroblasts are the production and turnover of the extracellular matrix. They secrete collagen, especially type I and III, as well as elastin, proteoglycans, and other matrix components. They also release enzymes such as matrix metalloproteinases that remodel the matrix and regulate tissue stiffness. In addition, fibroblasts respond to growth factors and cytokines, including transforming growth factor beta (TGF-β) and platelet-derived growth factor (PDGF), which influence their proliferation and activity.

During wound healing, fibroblasts migrate into the wound site and proliferate. They can differentiate into myofibroblasts, which express alpha-smooth muscle actin and contribute to wound contraction. While this is essential for timely closure, persistent myofibroblast activity can lead to excessive extracellular matrix deposition and scar formation, a process implicated in fibrotic diseases of the lung, liver, kidney, and skin.

Fibroblasts are heterogeneous and lack a universal set of markers. Commonly expressed proteins include vimentin, while activation markers such as fibroblast activation protein (FAP) may be present in some contexts. Beyond physiology, fibroblasts are used in tissue engineering to create ECM-rich scaffolds and study cell–matrix interactions.