Regeneration

regeneration (i.e., resolution of acute inflammation) requires an organ that is composed of cells that can divide and an intact basement membrane and connective tissue scaffolding.

  • Can occur in renewing tissues (e.g., gastrointestinal tract and skin).
  • Can occur in stable tissues (e.g., compensatory growth in the liver and kidney).
  • Regeneration requires an intact connective tissue scaffold.
  • Original architecture and structure of an organ or anatomic part is completely restored to the way it was before injury.
  • More primitive animals, such as small amphibians and reptiles, are still capable of this type of regeneration. However, as animals became larger and more complex during evolution, true regeneration was no longer possible. The human fetus is still largely capable of regeneration (especially in the early stages) but, in adults and with the possible exception of the liver (probably a compensatory enlargement and not regeneration), true regeneration does not take place.

replacement of damaged tissue with a scar

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Important mediators in repair

  • Epidermal growth factor (EGF): Stimulates granulation tissue formation.
  • Vascular endothelial growth factor (VEGF): Induces blood vessel formation.
  • PDGF: Promotes migration and proliferation of fibroblasts, smooth muscle cells, and monocytes.
  • FGF: Stimulates blood vessel formation and wound repair through macrophages, fibroblasts, and endothelial cell migration.
  • TGF-β: Acts as growth inhibitor for epithelium.

Stages of Wound Healing

 

Study Question

. A 54-year-old woman who has been diagnosed with early-stage breast cancer undergoes surgery for a lumpectomy to remove a small tumor detected by mammography. The pathology report confirms the early stage of the cancer and further comments on the fact that there is significant desmoplasia in the surrounding tissue. The term “desmoplasia” refers to

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    A. an irregular accumulation of blood vessels.

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    B. maturation and spatial arrangement of cells.

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    C. metastatic involvement of surrounding tissue.

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    D. normal tissue misplaced within another organ.

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    E. proliferation of non-neoplastic fibrous connective tissue.

 

The answer is E. Desmoplasia refers to proliferation of non-neoplastic fibrous connective tissue within a tumor and is quite common in cases of breast cancer.

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replacement of damaged tissue with a scar

 

USMLE Reviewer