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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=== | + | ==[[Fractures|Repair in the Bones]]== |
| − | * 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. [[Thyroid Gland - Pathology#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==
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| − | ===Causes of Fracture===
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| − | * The causes of fracture fit into two distinct categories:
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| − | *# '''Fracture of trauma'''
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| − | *#* Breakage of normal healthy bone due to excessive stress pressure of short duration.
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| − | *# '''Pathological fracture'''
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| − | *#* Breakage of bone weakened by some underlying metabolic, inflammatory or neoplastic condition.
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| − | | |
| − | ===Description of a Fracture===
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| − | * There are various terms to describe a fracture's appearance.
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| − | * Separation of the ends of the fracture may be '''complete''' or '''incomplete'''.
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| − | * When there is no penetration of the overlying skin, a the fracture is described as '''closed'''.
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| − | * When the sharp ends penetrate the overlying skin, the fracture is '''compound'''.
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| − | ** In this scenario there is the danger of introducing infection.
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| − | *'''Comminuted''' describes a fracture where there are multiple small fragments of bone at the site of breakage.
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| − | * Where the edges of the fracture are impacted into each other, the fracture is said to be '''compressed'''.
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| − | * When one side of the fracture is depressed below the plane of the other, the term '''depressed''' is used.
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| − | ** This occurs in the flat bones of the skull.
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| − | * '''Microfractures''' are fractures that are only visible on histological section as cracks in the bone.
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| − | ** Grossly, there might be evidence of some haemorrhage in the area.
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| − | | |
| − | ===Fracture Repair===
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| − | [[Image:fracture repair.jpg|thumb|right|150px|Fracture repair (Courtesy of BioMed Archive)]]
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| − | * On breakage, there is rupture of the periosteal, cortical and medullary vessels, causing:
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| − | ** A blood clot in the breakage area.
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| − | *** Fibrin is the important component.
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| − | ** Local necrosis of tissue supplied by these vessels.
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| − | *** This lowers the local pH.
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| − | * The fate of the blood clot depends upon its location.
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| − | ** The periosteal portion is lysed and disappears;
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| − | ** The medullary portion is removed by macrophages.
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| − | * The necrotic material is removed by phagocytosis.
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| − | ** Necrotic [[Bone Marrow - Anatomy & Physiology|bone marrow]] is removed by [[Macrophages|macrophages]].
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| − | *** This is a fairly rapid process.
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| − | ** Osteoclasts remove necrotic bone.
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| − | *** This is a slow process.
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| − | * On the periosteal side, the periosteum proliferates into the clot.
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| − | ** Forms a fibrous collar around the bone called the soft callus.
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| − | * The cells in the inner aspect of the soft callus, particularly those near the fracture fragments, differentiate into osteoblasts. [[Image:fracture callus.jpg|thumb|right|150px|Fracture callus (Courtesy of BioMed Archive)]]
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| − | ** Grow across the divide between the two fragments, laying down coarse woven bone.
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| − | * The woven bone laid is known as the hard callus.
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| − | ** This periosteal coarse bone is of utmost importance in repair.
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| − | *** It is responsible for much of the strength of the fracture repair.
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| − | ** This is replaced over a period of time by mature compact bone.
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| − | *** Aligns itself according to the stresses applied to it.
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| − | * Periosteal cells that are further away from the fracture fragments differentiate into cartilage-producing cells.
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| − | ** Produce a cone of cartilage between the two fragments.
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| − | *** As the local pH changes to more alkaline conditions, this cartilage undergoes calcification, with invasion by blood vessels and osteoblasts.
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| − | **** The cartilage is replaced by bone - endochondral ossification.
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| − | * On the medullary side, the endosteum proliferates and invades the clot, laying down bone.
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| − | ** This bone may totally occlude the medulla and is later remodelled to reconstitute a patent lumen.
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| − | | |
| − | ===Complications===
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| − | * There are several possible complications that may arise in the repair of bone.
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| − | # Inadequate immobilisation of the fractured ends will lead to incomplete repair by callus formation.
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| − | #* An intervening mass of fibrocartilage remains, forming a false joint.
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| − | #** In some cases the false joint can even appear to form a synovial lining.
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| − | #* If the fractured ends are sufficiently far apart, no substantial callus forms.
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| − | #** The intervening space is taken up by connective tissue organisation.
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| − | # Failure to align the fractured ends in proper apposition to one another will produce excessive callus.
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| − | #* This takes a longer time to be remodelled by the adult compact bone.
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| − | # [[Healing and Repair - Pathology#Description of a Fracture|Comminution]] delays healing due to persistent irritation.
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| − | # Infection delays healing due to the effects of the toxins on theproliferating cells.
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| − | #* May give rise to a systemic infection affecting the rest of the body.
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| | ==Repair in the Respiratory Tract== | | ==Repair in the Respiratory Tract== |
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| | * Infectious droplets tend to deposit in the anterior ventral portions of the lobes. | | * Infectious droplets tend to deposit in the anterior ventral portions of the lobes. |
| | ** I.e. in the apical, cardiac and anterior portions of the diaphragmatic lobes. | | ** I.e. in the apical, cardiac and anterior portions of the diaphragmatic lobes. |
| − | * Airborne agents produce '''bronchopneumonia'''. | + | * Airborne agents produce [[Bronchopneumonia|'''bronchopneumonia''']]. |
| | ** So-called because the inflammation is initiated and centred upon the airways. | | ** So-called because the inflammation is initiated and centred upon the airways. |
| | * The usual appearance of bronchopneumonia in ruminants and the pig is as the name suggests. | | * The usual appearance of bronchopneumonia in ruminants and the pig is as the name suggests. |
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| | *** Air trapped distal to the blockage is gradually absorbed into the bloodstream. | | *** Air trapped distal to the blockage is gradually absorbed into the bloodstream. |
| | **** This causes increased pressure on the injured wall, dilating it further. | | **** This causes increased pressure on the injured wall, dilating it further. |
| − | *** This is a progressive process and results in irreversible dilatation of the airway lumen and is called '''bronchiectasis'''. | + | *** This is a progressive process and results in irreversible dilatation of the airway lumen and is called [[Bronchiectasis|'''bronchiectasis''']]. |
| | * Bronchopneumonia in the dog and cat often tends to be more diffusely spread. | | * Bronchopneumonia in the dog and cat often tends to be more diffusely spread. |
| | ** These species have a poorly-developed interlobular septum and collateral ventilation between alveoli from different respiratory units. | | ** These species have a poorly-developed interlobular septum and collateral ventilation between alveoli from different respiratory units. |
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| | ===Blood-borne Agents=== | | ===Blood-borne Agents=== |
| | * Blood-bourne agents tend to have a patchy distribution throughout the lung. | | * Blood-bourne agents tend to have a patchy distribution throughout the lung. |
| − | * Cause '''interstitial pneumonia'''. | + | * Cause [[Interstitial Pneumonia|'''interstitial pneumonia''']]. |
| | | | |
| | ====Circulating Toxins==== | | ====Circulating Toxins==== |
| − | * For example, "Fog Fever" in adult cattle. | + | * For example, [[Acute Bovine Pulmonary Emphysema and Oedema|"Fog Fever"]] in adult cattle. |
| | ** Interstitial emphysema. | | ** Interstitial emphysema. |
| | ** 3-methyl indole is selectively toxic to Type 1 alveolar epithelium. | | ** 3-methyl indole is selectively toxic to Type 1 alveolar epithelium. |
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| | *** E.g. [[Salmonella|''Salmonella'']] | | *** E.g. [[Salmonella|''Salmonella'']] |
| | ** Protozoa | | ** Protozoa |
| − | *** E.g. [[Toxoplasma]] | + | *** E.g. ''[[Toxoplasma gondii]]'' |
| | | | |
| | ====Parasites==== | | ====Parasites==== |
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| | ** Stake wounds in horses. | | ** Stake wounds in horses. |
| | *** Usually fatal and cause extensive purulent, smelly inflammation. | | *** Usually fatal and cause extensive purulent, smelly inflammation. |
| − | ** Purulent pleuritis in dogs and cats due to ''[[Nocardia]]'' from a distant wound. | + | ** Purulent pleuritis in dogs and cats due to ''[[:Category:Nocardia species]]'' from a distant wound. |
| | *** Not uncommon in cats. | | *** Not uncommon in cats. |
| | *** May take some time to develop fully after the initial wound or cause has healed. | | *** May take some time to develop fully after the initial wound or cause has healed. |
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| | **# Chronic mastitis. | | **# Chronic mastitis. |
| | **#* Results in progressive destruction of the glandular tissue and replacement by fibrous tissue. | | **#* Results in progressive destruction of the glandular tissue and replacement by fibrous tissue. |
| − | **#* E.g. [[Streptococcal mastitis - bovine|''Streptococcus agalactiae'']]. | + | **#* E.g. [[Streptococcal Mastitis - Cattle|''Streptococcus agalactiae'']]. |
| | ** Some organisms such as [[Staphylococcus aureus|''Staphylococcus aureus'']] can cause gangrenous, acute and chronic mastitis. | | ** Some organisms such as [[Staphylococcus aureus|''Staphylococcus aureus'']] can cause gangrenous, acute and chronic mastitis. |
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| | ** Purulent meningitis follows haematogenous spread of infection from umbilical infections and certain septicaemias. | | ** Purulent meningitis follows haematogenous spread of infection from umbilical infections and certain septicaemias. |
| | [[Category:Inflammation|B]] | | [[Category:Inflammation|B]] |
| | + | [[Category:General Pathology]] |