The end stage of host response to tissue injury; a phenomenon consisting of sequentially controlled, chemically mediated steps which result in the replacement of dead tissue with regenerated cells and/or scar tissue
If an injury does not involve structural damage to the tissue, and regeneration of new cells can restore original function
In an injury, if there is at least some degree of connective tissue scarring and functional impairment of the involved tissue
These are cells which continuously regenerate throughout life to replace other cells that are lost through normal physiological processes (all epithelial surfaces, ducts, lymphoid and hematopoietic tissue, etc). These cells are continuously in the replicative cell cycle and replacement of damaged cells is relatively rapid.
These are cells that do not have the ability to regenerate. These include striated and cardiac muscle cells and neurons (neurons of the peripheral nervous system are capable of regenerating axons along the lines of the destroyed axon as long as the cell body is not damaged, but neurons of the central nervous system cannot regenerate).
These are cells which retain the ability to regenerate but do not do so under normal circumstances (hepatocytes, renal tubular epithelial cells, glandular parenchymal cells, endothelial cells, mesenchymal cells, etc). These cells are in the G0 phase of the cell cycle and the mechanism(s) by which these cells are stimulated to reenter the G1 phase of the cell cycle and proliferate is not entirely known.
Current hypotheses for how stable cells are stimulated to reenter the G1 phase of the cell cycle and proliferate (3)
Stimulation of Growth Factors
Loss of Contact Inhibition
Decrease in Cellular Density
Polypeptide proteins which attach to cell membrane receptor sites on various types of cells and either promote DNA replication (progression factors) or "prime" the cell for DNA replication (competence factors)
When growth factors promote DNA replication, they are known as
When growth factors "prime" the cell for DNA replication, they are known as
A scar in medical jargon
Approximately eighteen different forms of collagen have been identified and each has a distinctive distribution in the various tissues of the body. Which type is the predominant collagen in skin, bone, and most organs?
What vitamin is used as a co-factor for procollagen?
This refers to the repair process involved with surgical incisions where the margins of the wound are closely coapted by sutures or other methods. There is very little loss of tissue substance and a minimal amount of inflammatory exudate and necrotic debris.
Healing by First Intention (Primary Union)
Steps of Healing by Intention (Primary Union) (6)
When does inflammation begin in healing by first intention?
Within the first 24 hours
True or False:
Beneath the scab, in response to various stimuli, surface epithelial cells from the wound margins begin to proliferate and migrate toward the midline within 24 hours of the injury, and by 48 hours a tenuous single layered epithelium covers the surface of the wound.
When are fibroblasts from the healthy wound margin "activated" in healing by first intention
By the second day
Combination of neovascularity, "activated" fibroblasts and mixed inflammatory infiltrate (mostly macrophages) embedded in an edematous ground substance
When is granulation tissue generally present by in healing by first intention?
By the fifth day
This refers to the repair process involved when there is sufficient loss of tissue to prevent coaptation of the wound margins (abscesses, ulcers, infarctions, etc.). Generally, there is extensive inflammatory exudate and necrotic debris that must be removed before healing can occur. In this
situation, there is a slow, gradual buildup of granulation tissue beginning at the margins of the wound and growing inward at a rate of approximately 0.1 - 0.2 mm/day. The exposed granulation tissue is subject to trauma, and due to the delicate nature of the newly formed capillaries, is prone to bleed. Migration of surface epithelium can progress only so far as the underlying granulation tissue and therefore it takes longer for the wound to be isolated from the surrounding environment increasing the likelihood of infection. Wound contraction occurs in this.
Healing by Second Intention (Secondary Union)
This occurs in healing by second intention. Since the wound margins cannot be coapted, myofibroblasts (fibroblasts containing myofilaments) at the edges of the wound contract and can significantly reduce the volume of the area that must be filled with granulation tissue and subsequent scar. Although usually advantageous, this can occasionally be deleterious in that it may lead to disfiguring scars, "frozen" joints, etc
True or False:
As soon as granulation tissue is established and fibroblasts begin to secrete new collagen, the tensile strength of a wound begins to increase. There is resorption and remodeling of collagen as it is deposited, but the total collagen content of a wound increases faster than the tensile strength of a wound. After approximately 100 days, seventy to ninety percent of the original tissue strength is restored, but a scar is never as strong as the original tissue and is non-functional in terms of parenchymal function.
Early in wound healing, type ___ collagen is secreted, but as the scar matures and the collagen is remodeled, Type ___ collagen becomes predominant.
Type III; Type I
Collagen type that has a relatively low tensile strength
This refers to the excessive buildup of granulation tissue which protrudes above the surface of the wound and prevents re-epithelialization.
Exuberant Granulation (Proud Flesh)
This refers to a buildup of excessive amounts of collagen leading to disfiguring scars. Although the cause is unknown, there does seem to be a genetic predisposition to forming these scars.