Cellular Repair Flashcards
What cell type plays a central role in repair?
Activated M2 type macrophages
Clear agents, provide growth factors, stimulate fibroblast proliferation
What is regeneration?
Proliferation of cells that survive the injury and retain the capacity to proliferate
Tissue stem cells may also contribute to this process
How does a tissue repair itself if regeneration is not possible?
Connective tissue deposition
What is fibrosis?
Extensive deposition of collagen that occurs in the lungs, liver, kidney, and other organs as a consequence of chronic inflammation
Can be responsible for organ dysfunction and failure
What is organization?
Fibrosis develops in a tissue space occupied by an inflammatory exudate
E.g. organizing pneumonia
What are labile tissues?
Cells of these tissues are continuously being lost and replaced by maturation from tissue stem cells and proliferation of mature cells
Most surface epithelia, cuboidal epthilia of exocrine organs
What are stable tissues?
Cells of these tissues are quiescent and have only minimal proliferative activity
The parenchyma of most solid tissues, exception is liver
What are permanent tissues?
The cells of these tissues are considered to be terminally differentiated and nonproliferative in postnatal life
Brain, Heart, most muscle
What are the three components of connective tissue repair (scar formation)?
Angiogenesis
Formation of granulation tissue
Remodeling of connective tissue
What is angiogenesis?
Formation of new blood vessels to supply nutrients and oxygen to support the repair process
Why are newly formed vessels leaky and what does this contribute to?
Incomplete interendothelial junctions and VEGF increases vascular permeability
Accounts for edema that may persist in healing wounds long after the acute inflammatory response has resolved
How does granulation tissue form?
Migration and proliferation of fibroblasts and deposition of loose connective tissue, together with the vessels and interspersed leukocytes
What is connective tissue remodeling?
Maturation and reorganization of the connective tissue produce the stable fibrous scar
How does infection affect tissue repair?
Prolongs inflammation and potentially increases the local tissue injury
How does diabetes affect tissue repair?
Comprises tissue repair through many mechanisms and is one of the most important systemic causes of abnormal wound healing
How does nutritional status affect wound repair?
Things like protein deficiency and vitamin C deficiency inhibits collagen synthesis and retards healing
How do glucocorticoids affect healing?
May result in weakness of the scar due to inhibition of TGF-B production and diminished fibrosis
May be desirable, e.g. corneal infections to reduced opacity from collagen deposition
How does the type and extent of tissue injury affect healing?
Extensive injury will probably result in incomplete tissue regeneration and at least partial loss of function, even in tissues composed of stable and labile cells
What is resolution?
Repair of inflammation arising in tissue spaces developing extensive exudates
Occurs by digestion of the exudate by proteolytic enzymes of leukocytes and resorption of the liquified exudate
What is healing by first intention?
When injury only involves the epithelial layer
Rapid activation of coagulation
By day 3, neutrophils have been replaced by macrophages and granulation tissue
By day 5 neovascularization reaches its peak as granulation tissue fills the incisional space
What is healing by second intention?
Occurs when cell or tissue loss is more extensive
Wound contraction by the action of myofibroblasts
What are hypertrophic scars and Keloid similarities?
Accumulation of excessive amounts of collagen
What are characteristics specifically of keloids?
Extend beyond site of original injury
Rarely regress and continue to be composed of nodular whorls
Recur
More likely in dark pigmented skin
What is Proud Flesh?
Formation of extensive amounts of granulation tissue, which protrudes above the level of the surrounding skin and blocks reepithelialization
What are two complications of inadequate granulation?
Wound dehiscence
Ulceration
