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Healing and Repair - Pathology (view source)
Revision as of 15:14, 21 February 2011
, 15:14, 21 February 2011→Repair in the Skin
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''Back to [[Integumentary System - Pathology|Integumentary System Pathology]]
−* Healing of a wound or surgical incision may be by:
−** '''First intention'''
−** '''Second intention'''.
−
−===Healing by First Intention===
−* Healing by first intention occurs when the incised ends remain in close apposition to each other anf bacterial contamination is minimal.
−** This may be induced by suturing.
−** For example, a surgical incision.
−* Results in minimal scarring.
−
−====Process====
−* Initially, the incision ruptures the dermal blood vessels.
−** The exuded blood forms a fibrinous clot between and above the incision.
−*** The clot functions to:
−***# Stem the flow of blood from the injured site.
−***# Adhere the two ends together.
−***# Prevent infection from entering the injured area.
−* The basal layer of epithelium wthin 1mm of the wound edge begins to lose its connections with adjacent basal and overlying epithelium.
−** Undergoes mitosis.
−** Begins to migrate down both sides of the wound under the clot using pseudopodia.
−*** As they are migrating, cells differentiate to some degree to form more superficial layers of the epithelium.
−**** Gives a rather thick, if not very strong, barrier of epidermis.
−*** In the area of migration, the skin is usually hypopigmented and lacks hair follicles.
−* Within 2-4 days, the migrating basal layer of epithelium from either side meet together under the clot.
−** It is thought that there is passage of substances, from one side to another that prevents further migration and mitosis.
−** This gives reconstituion of an intact barrier to micro-organisms.
−* While the epithelial changes are occuring, there is a sudden proliferation of local fibroblasts and accompanying endothelial cells in the dermis surrounding the incision.
−** These grow across the narrow divide from each side and link up in the middle.
−*** Takes about 12 hours to accomplish.
−** 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.
−** This dermal repair forms the major portion of strength between the two sides at this time.
−*** Gains in strength over a long period of time as the collagen contracts and remodels according to the stresses imposed upon it.
−
−====Factors Inhibiting Healing====
−* Factors inhibiting proper wound healing include:
−*# '''Protein deficiency'''
−*#* May be absolute, as in starvation, or resolute, as in some of the endocrine deficiencies.
−*#** E.g. [[Hypothyroidism|hypothyroidism]]
−*# '''Vitamin C deficiency '''
−*#* Vitamin C is essential for fibroplasia and to maintain the integrity of endothelial and epithelial cells.
−*# '''Cold'''
−*# '''Ageing'''
−*# '''Contamination'''
−*#* Infection tends not to be a complication as bacteria are generally excluded.
−*#** Retained foreign material such as hair portions or suture material inadvertently left in the wound will cause infection and/or a foreign body reaction.
−*# '''Movement'''
−*#* Gives persistent trauma.
−
−===Healing by Second Intention===
−* Healing by second intention occurs when the gap between the ends of the incision is too wide to allow close approximation of the ends.
−* This process of granulation tissue repair in a large wound is also the underlying process in the repair of:
−** Infarcts and thrombi in vessels.
−** Surface ulcers and diphtheresis.
−** Pyogenic membrane in abscesses.
−** Diffuse fibrosis ( cirrhosis ) in the [[Liver - Anatomy & Physiology|liver]].
−
−====Process====
−* 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.
−* There is also considerable surface exudation.
−** The exudate is composed of fibrinous fluid and numerous inflammatory cells, mainly [[Neutrophils|neutrophils]] and macrophages.
−*** The cells are scavengers, and engulf necrotic debris and any bacteria present
−*** Macrophages and their secretions are also important for the promotion of fibroplasia.
−* The fibroblasts tend to align themselves roughly horizontal to the surface, but the endothelium is perpendicular to the surface.
−** The upper vessels form loops near to the surface.
−*** Gives the gross appearance of red granules - this is [[Granulation Tissue|granulation tissue]].
−* 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.
−** Infection is therefore a common complication in the early stages of healing.
−* Once the gap has been filled with granulation tissue and is free of infection, the epithelium migrates across.
−** As it migrates, the epithelium secretes collagenolytic substances.
−* The epidermis is usually hypopigmented and lacks hair follicles unless they have survived in the granulation tissue.
−
−==== Factors Inhibiting Healing====
−* Several factors inhibit healing by second intention.
−*# '''Movement'''
−*#* Movement before sufficient strength has been attained in the bond between the edges can inhibit healing.
−*# '''Infections'''
−*# '''Corticosteroids'''
−*#* Prevent proper collagen matrix formation.
−*#* Inhibit leukocyte emigration and phagocytosis.[[Image:scar tissue.jpg|thumb|right|150px|Scar tissue (Courtesy of BioMed Archive)]]
−*#* Diminish any acute inflammatory response by generally stabilising cellular membranes.
−
−====Scarring====
−* As the fibroblasts mature into fibrocytes, the collagen also matures and contracts and there may be extensive scar formation.
−** There may be considerable depression of the surface in such a scar.
−** The scar may interfere with movement in the area.
−* 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.
** This classical dual replacement gives rise to granulation tissue.
** This classical dual replacement gives rise to granulation tissue.
−==Repair in the Skin==
+==[[Skin Repair|Repair in the Skin]]==
−==Repair in the Bones==
==Repair in the Bones==