Tissue Repair and Healing Flashcards
what is healing
a process where the body replaces dead tissue with living tissue
ways in which healing can occur
- resoultion = complete restoration to normal = structurally and functionally
- regeneration = proliferation of parenchymal cells with loss of normal tissue architecture
- organization = lost/damaged tissue is replaced with granulation tissue = fibrous repair
on what condition does resolution occur
when the underlying framework is preserved
which processes can occur together
regeneration and organization
labile cells
- cells that are constantly multiplying
- includes cell surface epithelia that cover the body or line hollow organs, cells bone marrow and haematopoetic cells
stable cells
- cells that divide in response to a stimuli= there needs to be the normal cells left behind for regeneration to take place
- usually slow replicating
- can return the tissue to its origin
- parenchymal cells of the liver, kidneys and pancreas, mesenchymal cells such as fibrobalsts and smooth muscles and resting cells such as lymphocytes and leukocytes
permanent cells
- unable to undergo mitotic division in postnatal life
- neurons, skeletal muscles and cardiac tissues
- damage to the tissue results in healing by replacement by scar formation
granulation tissue
new connective tissue and blood vessels formed suring the healing process
what are stem cells
undifferentiated cells that either self- renew or differentiate into specialised cells.
they are present mainly in labile and stable cells
stem cells location - 5
- epidermis
- basal layer adjacent to the basement membrane
- hair follicles and sebbaceous glands
- intestinal mucosa
- bottom of the crypts
- seperate pool in the bone marrow where these haematopoetic stem cells seed into other organs and differentiate locally into the appropriate tissue
the cells of the liver
the liver has an equivalent population of progenitor cells laying between the hepatocytes and bile duct
stem cell differentiation is reliant on
the integrity of the stem cell population
when permenant cells are abundant
there is dominant connective tissue with eventual laying down of the ECM particularly collagens = granulation tissue forms
when labile and stem cells are abundant
there is efficient regeneration of stem cell activity
what is toxic to stem cells
- they are vulnerable to radiation injury
- results in their loss limiting their regeneration ability
- results in mutations that propagate to daughter cells with the risk of neoplastic transformation
examples of healing in terms of
- resolution = lungs
- regeneration - liver
- organization - heart
when does scarring occur
- in severe or chronic injury which affects the epithelia, connective tissue framework and parenchymal cells
- it also occurs in cells that are non dividing (permanent)
define scar formation - 2
- a response that “patches” rather than restores the tissue
- it is alsor the replacement of parenchymal cells with collagen
what happens if resolution does not occur
fibroblasts and endothelial cells begin to proliferate and form a specialized type of tissue called granulation tissue
appearance of granulation tissue
pink, soft, granular appearance
what is in the granulation tissue
MEF + inflammatory cells, particularly macrophages
the amount of granulation tissue formed depends on
- size of injury
- intensity of inflammation
histologic appearance of granulation tissue -4
- fibroblasts
- new thinwalled delicate capillaries (angiogenesis)
- loose ECM
- an admix of inflammatory cells - macrophages
how does a scar TISSUE form - 2
- as fibrosis proceeds, the new blood vessels thrombose and degenerate and the cells die and get reabsorbed
- maturation and organization of the cnt tissue produce a pale avascular fibrous scar
3 components of granulation tissue
- mucin rich ground substance
- endothelial cells/capillaries
- fibroblasts
connected processes in first intention healing-3
- inflammation
- proliferation of epithelial and other cells
- maturation of the connective tissue scar
2 more points on scar tissue formation
- collagen fibres orientate in a way to resist stress
- contraction of the scar follows (scar basically shrinks)
what is a cutaneous wound?
A cutaneous wound is a wound that affects the skin. It can be caused by trauma, cuts, abrasions, surgical incisions, burns, or other injuries to the skin’s surface. These wounds may involve different layers of the skin, such as the epidermis, dermis, or even deeper tissue.
what does healing involve
- epithelial regeneration
- formation of connective tissue
healing by first intention (primary union) - 4
- injury involves only the epithelial layer
- through epithelial regeneration
- clean uninfected wpunds
- little disruption to the basement membrane, loss of few epithelial and cnt tissue cells
healing by second intention (secondary union)
- wound has seperated edges
- inflammation is more intense
- development of abundant granulation tissue
- accumulation of ECM
- process is much slower
what then results in second intetnion healing
- formation of a large scar
- wound contraction by myofibroblasts (which is very minimal in first intention!!)
which healing results in epithelial overgrowth
second intention
difference between secondary and primary healing- LIG DW
Large tissue deficits which result into larger firbin clot, more exhudate and necrotic debris in the wounded area
Inflammation is more intense because large tissue deficiets have more fibrin clot, exhudate and necrotic debris that need to be removed
Granulation tissue is larger to fill in the gaps and there is a greater mass of scar tissue
Dermal appendages that have been destroyed in the line of inclision are permanently lost
Wound contraction generally occurs in large syrface wounds
what does wound strength depend on
the formation of the right type of collagen
how is collagen synthesised
synthesized by fibroblasts and released into the ECM as procollagen due
fibrils
fine, thread-like structures made of proteins like collagen or actin, important for structural support in tissues and cells. (like pili)
true fibrils
joint together by cross linkages to provide additional strength
3 functions of collagen
- structural support
- skin elasticity
- tissue repair
Type III collagen vs Type I
III is laid down early but is less strong and so is replaced with type I
recovery of tensile strength
- in the first two months recovery of strength is due to excess collagen production over collagen degradation
- and then later its due to the structural modification of collagen fibers
how does wound strength improve
70-80% after 3 months but never goes beyond that
local factors affecting wound healing
Hypoxia/anoxia
Infection
Foreign body
Movement
Irradiation
Corticosteroids
Size
systemic factors affecting wound healing
Age
Inadequate nutrition
Diabetes mellitus
Corticosteroids
complications of wound healing - PICK WOM
Pain - neuroma formed by proliferation of nerve fibres caught up in the wound
Infection - tissue desctruction/ pus formation
Cicatrisation = SOC
Keloid - excess production of matured collagen forming a lump in the scar
Weakness- reduced tensile strength of fibrous scar tissue
Oovergrowth of granulation tissue preventing reepitheliazation
Malignant tranformation - chronic scarred ulcers
