Skin Repair

2011-06-11T09:38:47Z

Barnowl68: /* Healing by First Intention */

* 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 and 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.

[[Category:Integumentary System - Pathology]]

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Skin Repair