Tissue Repair

Regeneration of injured cells by cells of same type, for example regeneration of skin/oral mucosa

Replacement by fibrous tissue (fibroplasia, scar formation)

Both require cell growth, differentiation, and cell-matrix interaction

Varieties of Proliferative Potential

Stable (quiescent) cells:◦Normally little proliferation but remain

capable of more rapid cell division following injury.

◦Liver, kidney, pancreas, endothelium, fibroblasts

◦Chances of regeneration are GOOD

Varieties of Proliferative Potential

Labile (always dividing) cells: ◦Replace dying cells◦Epithelial cells of the skin, oral cavity,

exocrine ducts, and GI tract; endometrial and bone marrow cells.

◦Chances of regeneration are EXCELLENT

Varieties of Proliferative Potential

Permanent (non-dividing ) cells:◦Not capable of proliferation.◦Irreversible injury leads only to scar◦Nerve cells, myocardium, skeletal

muscle,

Cell Cycle

Cell Signaling PatternsAutocrine = ligand is secreted and

detected by same cell

Paracrine = ligand is secreted and separately detected by neighboring cells

Endocrine = ligands (usually hormones) are secreted into the vasculature to affect distant target cells

Wound healing

Healing by first intension (primary)This occurs in clean, incised

wound with good apposition of the edges.

24 hours

3 to 7 days

WEEKs

Healing by second intension(secondary)

This occurs in open wound, particularly when there has been significant loss of tissue , necrosis or infection

24 hours

3 to 7 days

WEEKs

FIBROSISFibrosis, in general, refers to any

fibroblast proliferation with deposition of excess extracellular matrix which is mostly collagen.

Leads to functional loss.It is the end result of wound

healing

This is a healing biopsy site on the skin seen a week following the excision, The skin surface has re-epithelialized, and below this is granulation tissue with small capillaries and fibroblasts forming collagen.

Complications of Wounds• Deficient scar formation – wound

dehiscence/ ulceration

• Excess repair – keloid formation

• Excess contraction – joint contractures/ intra-abdominal adhesions