[PL3.3] Inflammation and Repair

Restoration of tissue architecture and function after injury

tissue repair

Process involving growth of cells and tissues to replace damaged components and return to a normal state

regeneration

Process involving deposition of connective tissue when regeneration is not possible

scar formation

Collagen deposition due to chronic inflammation in organs like lungs, liver, and kidney

fibrosis

The regeneration of injured cells and tissues involves cell proliferation driven by growth factors

cell and tissue regeneration

Restoration of normal tissue structure can occur only if this remains structurally intact

residual tissue

Tissue type where cells are continuously lost and replaced by stem cell maturation and proliferation of mature cells

labile tissues

Examples of labile tissues include: hematopoietic cells, stratified squamous epithelia, cuboidal and columnar epithelium, and transitional epithelium

examples of labile tissues

Tissue type that is quiescent but capable of division in response to injury

stable tissues

Examples of stable tissues include hepatocytes, renal tubular cells, mesenchymal cells, and parenchymal cells of glands

examples of stable tissues

Tissue type that is terminally differentiated and non-proliferative in postnatal life

permanent tissues

These tissues are replaced by scar tissues such as fibrosis or gliosis in the CNS

examples of permanent tissues

Examples include neurons and myocardial cells

examples of permanent (non-dividing) tissues

If repair cannot be accomplished by regeneration alone, what process replaces injured cells with connective tissue?

repair by connective tissue deposition

What is the end result of connective tissue deposition in tissue repair?

scar formation

What is the first step in scar formation where mediators recruit inflammatory cells to eliminate the offending agent?

inflammation

How long does the inflammatory phase in scar formation typically last?

6 to 48 hours

What is the second step in scar formation involving proliferation and migration of several cell types?

cell proliferation

What type of tissue forms from migrating and proliferating fibroblasts and has a pink, soft, granular appearance?

granulation tissue

What is the final step in scar formation where granulation tissue is replaced by collagen?

deposition of connective tissue

What type of wound healing occurs when injury involves only the epithelial layer?

Healing by first intention / primary union / epithelial regeneration

Give an example of healing by first intention.

Healing of a clean, uninfected surgical incision approximated by surgical sutures

What happens immediately after injury in first intention healing?

Rapid activation of coagulation pathways leading to clot formation

Which immune cells are present within 24 hours in the incision margin during first intention healing?

Neutrophils

By which day are neutrophils largely replaced by macrophages and granulation tissue appears in the incision space?

Day 3

When does neovascularization reach its peak in first intention healing?

Day 5

What happens by week 2 in first intention wound healing?

Collagen accumulation and fibroblast proliferation

What characterizes the scar at the end of the first month of first intention healing?

Cellular connective tissue with few inflammatory cells, covered by essentially normal epidermis

When does healing by second intention occur?

In large, open wounds, abscesses, ulceration, or ischemic necrosis in parenchymal organs with significant tissue loss

What are key features of healing by secondary union?

Wound contraction, more intense inflammatory reaction, more granulation tissue than primary union

How does the fibrin clot in secondary union compare to primary union?

Larger fibrin clot

What accumulates more in the wounded area during secondary union?

More exudate and necrotic debris

What is the nature of the inflammatory response in secondary union?

More intense inflammation

How much granulation tissue is formed in secondary union compared to primary union?

Larger amounts of granulation tissue

What results from the larger granulation tissue mass in secondary union?

Greater mass of scar tissue

What important feature occurs in large surface wounds in secondary healing?

Wound contraction