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| | ** This classical dual replacement gives rise to granulation tissue. | | ** This classical dual replacement gives rise to granulation tissue. |
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| − | ==Repair in the Skin== | + | ==[[Skin Repair|Repair in the Skin]]== |
| − | ''Back to [[Integumentary System - Pathology|Integumentary System Pathology]]
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| − | * Healing of a wound or surgical incision may be by:
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| − | ** '''First intention'''
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| − | ** '''Second intention'''.
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| − | ===Healing by First Intention===
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| − | * Healing by first intention occurs when the incised ends remain in close apposition to each other anf bacterial contamination is minimal.
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| − | ** This may be induced by suturing.
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| − | ** For example, a surgical incision.
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| − | * Results in minimal scarring.
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| − | | |
| − | ====Process====
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| − | * Initially, the incision ruptures the dermal blood vessels.
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| − | ** The exuded blood forms a fibrinous clot between and above the incision.
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| − | *** The clot functions to:
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| − | ***# Stem the flow of blood from the injured site.
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| − | ***# Adhere the two ends together.
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| − | ***# Prevent infection from entering the injured area.
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| − | * The basal layer of epithelium wthin 1mm of the wound edge begins to lose its connections with adjacent basal and overlying epithelium.
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| − | ** Undergoes mitosis.
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| − | ** Begins to migrate down both sides of the wound under the clot using pseudopodia.
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| − | *** As they are migrating, cells differentiate to some degree to form more superficial layers of the epithelium.
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| − | **** Gives a rather thick, if not very strong, barrier of epidermis.
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| − | *** In the area of migration, the skin is usually hypopigmented and lacks hair follicles.
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| − | * Within 2-4 days, the migrating basal layer of epithelium from either side meet together under the clot.
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| − | ** It is thought that there is passage of substances, from one side to another that prevents further migration and mitosis.
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| − | ** This gives reconstituion of an intact barrier to micro-organisms.
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| − | * While the epithelial changes are occuring, there is a sudden proliferation of local fibroblasts and accompanying endothelial cells in the dermis surrounding the incision.
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| − | ** These grow across the narrow divide from each side and link up in the middle.
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| − | *** Takes about 12 hours to accomplish.
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| − | ** In the early stages (days 4-7), their alignment may be vertical, but in later stages (7-21 days) both fibroblasts and capillaries line up horizontally across the incision.
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| − | ** This dermal repair forms the major portion of strength between the two sides at this time.
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| − | *** Gains in strength over a long period of time as the collagen contracts and remodels according to the stresses imposed upon it.
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| − | | |
| − | ====Factors Inhibiting Healing====
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| − | * Factors inhibiting proper wound healing include:
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| − | *# '''Protein deficiency'''
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| − | *#* May be absolute, as in starvation, or resolute, as in some of the endocrine deficiencies.
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| − | *#** E.g. [[Hypothyroidism|hypothyroidism]]
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| − | *# '''Vitamin C deficiency '''
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| − | *#* Vitamin C is essential for fibroplasia and to maintain the integrity of endothelial and epithelial cells.
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| − | *# '''Cold'''
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| − | *# '''Ageing'''
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| − | *# '''Contamination'''
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| − | *#* Infection tends not to be a complication as bacteria are generally excluded.
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| − | *#** Retained foreign material such as hair portions or suture material inadvertently left in the wound will cause infection and/or a foreign body reaction.
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| − | *# '''Movement'''
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| − | *#* Gives persistent trauma.
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| − | ===Healing by Second Intention===
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| − | * Healing by second intention occurs when the gap between the ends of the incision is too wide to allow close approximation of the ends.
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| − | * This process of granulation tissue repair in a large wound is also the underlying process in the repair of:
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| − | ** Infarcts and thrombi in vessels.
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| − | ** Surface ulcers and diphtheresis.
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| − | ** Pyogenic membrane in abscesses.
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| − | ** Diffuse fibrosis ( cirrhosis ) in the [[Liver - Anatomy & Physiology|liver]].
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| − | | |
| − | ====Process====
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| − | * In comparison to healing by first intention, there is a more massive fibroblastic and endothelial proliferation in the wound which fills and repairs the defect.
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| − | * There is also considerable surface exudation.
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| − | ** The exudate is composed of fibrinous fluid and numerous inflammatory cells, mainly [[Neutrophils|neutrophils]] and macrophages.
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| − | *** The cells are scavengers, and engulf necrotic debris and any bacteria present
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| − | *** Macrophages and their secretions are also important for the promotion of fibroplasia.
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| − | * The fibroblasts tend to align themselves roughly horizontal to the surface, but the endothelium is perpendicular to the surface.
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| − | ** The upper vessels form loops near to the surface.
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| − | *** Gives the gross appearance of red granules - this is [[Granulation Tissue|granulation tissue]].
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| − | * Well-formed granulation tissue tends to be fairly resistant to surface infection; however, it is rather delicated and so susceptible to trauma and subsequent introduction of infection.
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| − | ** Infection is therefore a common complication in the early stages of healing.
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| − | * Once the gap has been filled with granulation tissue and is free of infection, the epithelium migrates across.
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| − | ** As it migrates, the epithelium secretes collagenolytic substances.
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| − | * The epidermis is usually hypopigmented and lacks hair follicles unless they have survived in the granulation tissue.
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| − | | |
| − | ==== Factors Inhibiting Healing====
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| − | * Several factors inhibit healing by second intention.
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| − | *# '''Movement'''
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| − | *#* Movement before sufficient strength has been attained in the bond between the edges can inhibit healing.
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| − | *# '''Infections'''
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| − | *# '''Corticosteroids'''
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| − | *#* Prevent proper collagen matrix formation.
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| − | *#* Inhibit leukocyte emigration and phagocytosis.[[Image:scar tissue.jpg|thumb|right|150px|Scar tissue (Courtesy of BioMed Archive)]]
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| − | *#* Diminish any acute inflammatory response by generally stabilising cellular membranes.
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| − | | |
| − | ====Scarring====
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| − | * As the fibroblasts mature into fibrocytes, the collagen also matures and contracts and there may be extensive scar formation.
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| − | ** There may be considerable depression of the surface in such a scar.
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| − | ** The scar may interfere with movement in the area.
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| − | * The scar tends to diminish in size over a long period of time, as the underlying collagen remodels according to the stresses imposed upon the area.
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| | ==Repair in the Bones== | | ==Repair in the Bones== |