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| | ==[[Skin Repair|Repair in the Skin]]== | | ==[[Skin Repair|Repair in the Skin]]== |
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| − | ==Repair in the Bones== | + | ==[[Fractures|Repair in the Bones]]== |
| − | ===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)]] | |
| − | * 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=== | |
| − | * 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''']]. |
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| | ====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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| | **# 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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