Chapter 3: Repair Flashcards
Repair of damaged tissues occurs by two types of reactions. Those are?
- Regeneration by proliferation of residual (uninjured) cells and maturation of tissue stem cells.
- Deposition of connective tissue to form a scar.
What is meant by the process of regeneration?
Tissues that are able to replace damaged components and essentially return to a normal state.
Regeneration is possible when…
cells survive the injury and retain the capacity to proliferate.
Is regeneration always possible –> can an injured tissue heal completely?
No, mammals have a limited capacity to regenerate damaged tissue and organs, only some components of most tissues are able to fully restore themselves.
When does repair through scar formation occur?
If the
injured tissues are incapable of complete restitution, or if the supporting structures of the tissue are severely
damaged, repair occurs by the laying down of connective (fibrous) tissue.
What’s the difference between scarring and fibrosis?
A scar is a means to repair damaged tissue and occurs by the layering of connective (fibrous) tissue. Fibrosis is the extensive deposition of collagen that occurs in the lungs, liver, kidney, and
other organs as a consequence of chronic inflammation,
or in the myocardium after extensive ischemic necrosis
(infarction).
What is meant by organization (of fibrosis)?
This is when fibrosis develops in a tissue space occupied by an inflammatory exudate.
Which cells will (and can) proliferate during tissue repair?
Remnants of injured tissue, vascular endothelial cells and fibroblasts.
What is the definition of labile tissues?
In some tissues cells are constantly being lost and must be continually replaced by new cells that are derived from tissue stem cells and rapidly proliferating immature progenitors.
Examples of labile tissues are: hematopoietic cells in the bone marrow and many surface
epithelia, such as the basal layers of the squamous epithelia
of the skin, oral cavity, vagina, and cervix; the cuboidal epithelia of the ducts draining exocrine organs (e.g., salivary
glands, pancreas, biliary tract); the columnar epithelium
of the gastrointestinal tract, uterus, and fallopian tubes;
and the transitional epithelium of the urinary tract
Examples of labile tissues are:
hematopoietic cells in the bone marrow and many surface
epithelia, such as the basal layers of the squamous epithelia
of the skin, oral cavity, vagina, and cervix; the cuboidal epithelia of the ducts draining exocrine organs (e.g., salivary
glands, pancreas, biliary tract); the columnar epithelium
of the gastrointestinal tract, uterus, and fallopian tubes;
and the transitional epithelium of the urinary tract
What is meant by stable tissue?
Tissue that is made up of cells that are normally in the G0 stage of the cell cycle and hence not proliferate, but they are capable of dividing in response to injury or loss of tissue mass.
Examples of stable tissues are:
the parenchyma of most solid organs, such as
liver, kidney, and pancreas.
Examples of stable tissues are:
the parenchyma of most solid organs, such as
liver, kidney, and pancreas.
What is special to endothelial cells, fibroblasts and smooth muscle cells?
They are termed as stable tissues, but can proliferate in a response to growth factors.
What is meant by permanent tissues?
Tissues that consist of terminally differentiated nonproliferative cells, such as the majority of neurons and cardiac muscle cells.
Injury of what kind of tissue (labile, stable or permanent) will result in scar formation?
Injury to permanent tissues.
Through which cells is some regenerative capacity for muscle possible?
Regeneration is possible through satellite cells attached to the endomysial sheath.
Growth factors are important for cell proliferation. Which type of cell is an important producer of growth factors during injury? Name two other sort of cells also.
Macrophages, and also epithelial and stromal cells.
What other signals can stimulate cell proliferation?
Cells use integrins to bind to ECM proteins, and signals from the integrins can also stimulate cell proliferation.
The importance of regeneration in the replacement of
injured tissues varies in different types of tissues and with
the severity of injury..
What happens to epithelia of the intestinal tract and skin when injured?
Injured cells are rapidly replaced by proliferation of residual cells and differentiation of cells derived from tissue stem cells, so that the underlying basement membrane stays intact.
Will the following example lead to complete regeneration or to scarring?
Liver abscess: extensive destruction of the liver with collapse of the reticulin framework.
This leads to scar formation even though the remaining liver cells have the capacity to regenerate.
Regeneration of the liver occurs by two major mechanisms: proliferation of remaining hepatocytes and repopulation from progenitor cells. By which cytokine and by which growth factor is the process of proliferation of hepatocytes following partial hepatectomy stimulated?
By IL-6 (produced by Kupffer cells) and by hepatocyte growth factor (HGF).
In situations in which the proliferative capacity of hepatocytes is impaired, such as after chronic liver injury or inflammation, which cells contribute to repopulation?
Progenitor cells.
Repair by connective tissue deposition consists of a series
of sequential steps that follow tissue injury. This begins by formation of a hemostatic plug comprised of platelets, in order to stop the bleeding. After this the process of inflammation starts, where (among others) M1- and M2-macrophages play an important role. This happens during the first 6-48 hours. What happens after this step and how long does this step take?
After inflammation, cell proliferation starts which takes up to 10 days.
What is the function of the following cells during cell proliferation of these cell types?
Epithelial cells.
Endothelial and other vascular cells.
Fibroblasts.
Epithelial cells respons to locally produced growth factors and migrate over the wound to cover it.
Endothelial and other vascular cells proliferate to form new blood vessels (angiogenesis).
Fibroblast proliferate and migrate into the site of injury and lay down collagen fibers that form a scar.
What is a granulation tissue?
The combination of proliferating fibroblasts, loose
connective tissue, new blood vessels and scattered
chronic inflammatory cells, forms a type of tissue that
is unique to healing wounds. This term derives from its pink, soft, granular
gross appearance, such as that seen beneath the scab
of a skin wound.
What is the step in repair by scarring after proliferation, what happens during this step?
Remodeling, The connective tissue that has been deposited by fibroblasts is reorganized to produce the stable
fibrous scar. This process begins 2 to 3 weeks after injury
and may continue for months or years.
What is the difference between healing by first intention (primary union) and healing by second intention (secondary union)?
Healing by first intention: epithelial regeneration with minimal scarring.
Healing by second intention: larger wound that heal by a combination of regeneration and scarring.
