Fibrosis

Fibrosis is the pathological accumulation of excess fibrous connective tissue in organs or tissues as a reparative or reactive process. While it can be a reactive or benign state, pathological fibrosis can severely compromise the function of the affected organ. The process may be termed scarring when it follows injury. Fibrosis that arises from a single cell line is labeled a fibroma. Essential to the wound healing process, fibrosis can nevertheless disrupt the normal architecture and function of the underlying organ or tissue when excessive. Predominantly characterized by the excessive accumulation of extracellular matrix (ECM) proteins, fibrosis essentially represents an overzealous wound healing response that can significantly hinder normal organ function.

Physiology

The physiological mechanisms underlying fibrosis bear a close resemblance to those of scarring; both processes involve the deposition of connective tissue by stimulated fibroblasts. Initiating factors often include soluble substances released by immune cells, such as macrophages. TGF beta, the most extensively studied pro-fibrotic mediator, is secreted by macrophages and the interstitium in damaged tissues. Other key soluble fibrosis mediators encompass CTGF, platelet-derived growth factor (PDGF), and interleukin 10 (IL-10). These molecules activate intricate signal transduction pathways, notably the AKT/mTOR and SMAD pathways, which stimulate fibroblast proliferation and activation, ultimately leading to the deposition of extracellular matrix in the surrounding connective tissue. Although vital for tissue repair, if this process becomes deregulated or encounters repetitive or severe tissue injuries, it can culminate in a progressive, irreversible fibrotic response.

Anatomical location

Fibrosis manifests in multiple body tissues, often as a result of damage or inflammation. The following are common examples:

Lungs

• • Pulmonary fibrosis
    • Cystic fibrosis
    • Idiopathic pulmonary fibrosis
  • Radiation-induced lung injury

Liver

• • Bridging fibrosis
  • Cirrhosis

Heart

• • Atrial fibrosis
  • Endomyocardial fibrosis
  • Post-myocardial infarction fibrosis

Brain

• • Glial scar

Other Tissues and Organs

• • Arterial stiffness
  • Arthrofibrosis
  • Crohn's disease
  • Dupuytren's contracture
  • Keloid
  • Mediastinal fibrosis
  • Myelofibrosis
  • Peyronie's disease
  • Nephrogenic systemic fibrosis
  • Progressive massive fibrosis
  • Retroperitoneal fibrosis
  • Scleroderma/systemic sclerosis
  • Certain forms of adhesive capsulitis

Incidence

Recent studies have highlighted the increasing incidence of fibrosis in various conditions. For instance, liver fibrosis due to chronic hepatitis C infection has emerged as a significant healthcare issue in several countries. Also, idiopathic pulmonary fibrosis has observed an uptick in incidence in the last two decades, making it a research priority in respiratory medicine.

See also

Fibroblast Granuloma Interstitial lung disease Scarring

Fibrosis Resources
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Classification	MeSH: D005355