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| − | ==Introduction== | + | {{frontpage |
| | + | |pagetitle =Acute Inflammation |
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| − | * Acute inflammation is characterised sudden onset and may last for a few hours to a few days.
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| − | * Vascular, humoral and cellular alterations cause the 5 cardinal signs as a result of exposure of tissues to various causes.
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| − | * Acute inflammation can:
| + | <categorytree mode=pages>Acute Inflammation</categorytree> |
| − | *# Be fatal
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| − | *# Resolve by regeneration in association with the host defence mechanisms.
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| − | *#* May be assisted by therapeutic measures.
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| − | *# Undergo repair by fibrosis.
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| − | *# Become chronic.
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| − | *#* First goes through a subacute phase.
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| − | *#* Is dependent upon the persistence of the agent and the amount of damage caused.
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| − | ==Sequence of Events==
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| − | * The following sequence of events is provoked by the presence of the irritant.
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| − | # '''Momentary vasoconstriction'''
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| − | #* Following contact with the irritant, there is momentary vasoconstriction of the blood vessels in the affected area.
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| − | #* This is reversed within minutes.
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| − | # '''Dilation of the blood vessels'''
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| − | #* Initially, dilation of the capillaries is caused by the release of chemical mediators.
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| − | #* Arterioles then dilate under the influence of a local axon reflex.
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| − | #* This gives rise to an initial acceleration of the blood flow to the area.
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| − | #** This later gives way to a slowing of blood flow, caused by alterations in vascular endothelial permeability and the filling of previously closed capillaries.
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| − | # '''Exudation of fluid'''
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| − | #* Follwing the slowing of blood flow and altered capillary permeability, a protein-rich fluid is exudated.
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| − | # '''Margination of leukocytes'''
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| − | #* Circulating white blood cells are attracted to the altered endothelial surfaces.
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| − | # '''Emigration of leukocytes'''
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| − | #* [[Leukocytes|Leukocytes]] migrate through the altered endothelium to reach the injured area.
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| − | #* This is an active process - [http://www.cellsalive.com/chemotx.htm| chemotaxis].
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| − | #** The cells are attracted to the endothelium by release of proteins, and further into the tissues by factors released from cells in the damaged area.
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| − | #** The emigrated leukocytes and components of the fluid exudate are also chemotactic.
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| − | #** More cells and fluid are attracted to the area.
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| − | # '''Emigration of red blood cells'''
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| − | #* [[Erythrocytes|Erythrocytes]] migrate through the gaps in the altered endothelium to the damaged tissue.
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| − | # '''Induction of an increase in temperature'''
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| − | #* This may occur either locally or systemically.
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| − | #* A systemic rise in temperature is known as pyrexia.
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| − | #** Occurs in generalise acute inflammation.
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| − | #** Pyrogens act on the temperature control centres in the hypothalamus, and are released from:
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| − | #*** [[Neutrophils|Neutrophils]], [[Eosinophils|eosinophils]] and [[Macrophages|macrophages]]
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| − | #**** Particulary [[Neutrophils|neutrophils]] when they begin to phagocytose.
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| − | #*** The cellular coat of gram-negative organisms.
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| − | #*** Necrosis of damaged tissue cells.
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| − | #*** Antigen-antibody complexes.
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| − | #*** Tumours.
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| − | #**** Particularly those which have metastasised
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| − | #**** It may be difficult to separate this from the pyrexia caused by the central necrosis in such tumours.
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| − | ==Fluids==
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| − | ===Serous===
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| − | * Serous fluids are formed due to mild vascular injury in an organ or in vessels underlying a
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| − | surface.
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| − | * The fluid is clear to cloudy fluid.
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| − | ** Little protein is present.
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| − | * Examples:[[Image:hand burn injury.jpg|right|thumb|150px|<small><center>'''Burn injury'''. (Courtesy of T. Scase)</center></small>]]
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| − | ** Vesicles of the skin.
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| − | ** Many inflammations in joints.
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| − | ===Catarrhal===
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| − | * Catarrhal inflammation is a mild form of inflammation.
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| − | * Occurs on mucous membranes where there are many mucus cells.
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| − | * The consistency of catarrhal exudate varies from water to gelatinous.
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| − | * Colour varies from cloudy to pinkish.
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| − | * This form of exudation is essentially a shedding of epithelium containing many mucus cells, neutrophils, some RBCs, and flecks of fibrin.
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| − | * Common in mild forms of rhinitis, tracheitis, bronchitis, gastritis and enteritis.
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| − | ===Fibrinous===
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| − | * Fibrinous exudation occurs in more severe endothelial injury.
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| − | ** Injury results in the escape of fibrinogen, which is converted to fibrin.
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| − | * The fibrin formed appears as a yellowish coagulation on the surface of or within a tissue.
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| − | ** Common in the lungs and on serous surfaces.
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| − | * In hollow organs the fluid may coagulate to form casts of the lumen.
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| − | * Fibrin will peel off from the underlying tissue without causing damage to it.
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| − | ===Diptheritic===
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| − | * Diphtheritic exudate a more severe form of fibrinous exudate in which there is considerable necrosis of the underlying tissues.
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| − | * Diptheritic exudate is firmly adherent to the underlying tissue.
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| − | ** Attempts at removal cause tearing of this tissue>
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| − | * Commonly seen with internal surface fungal infections.
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| − | ** E.g. in the nose of the dog and the guttural pouch of the horse.
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| − | ** Fungal toxins penetrate the underlying tissue causing coagulation necrosis.
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| − | ===Haemorrhagic===
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| − | * This is a severe acute to peracute inflammation in which haemorrhage is the main component.
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| − | * Seen in the lymph nodes, lungs and intestine in severe inflammation.
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| − | ===Purulent===
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| − | * In purulent inflammation, pus is the predominant feature.
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| − | ** Pus is an admixture of dead and dying neutrophils with necrotic cells and a pyogenic agent.
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| − | *** Proteolytic enzymes released by the dying neutrophils lyse tissue cells to produce a fluid.
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| − | * Colour varies depending upon the agent.
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| − | ** May be white, yellow, green or brown.
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| − | * An abscess is a circumscribed sphere of pus surrounded by a pyogenic membrane.
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| − | ** The pyogenic membrane is composed of capillaries bringing neutrophils into the sphere.
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| − | ** This rapidly becomes enveloped by a fibrous tissue capsule.
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| − | *** A local connective tissue response attempting to wall off the purulent irritant from nearby normal tissue.
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| − | ===Functions of Exudate===
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| − | # Dilutes the toxic agent, reducing its effect upon the tissue cells.
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| − | # The protein components may contain antibodies which attack or coat (opsonise) the irritant.
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| − | #* This makes the irritant more digestible to neutrophils and macrophages.
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| − | # Exudates may contain fibrin.
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| − | #* This is very sticky - immobilises the irritant.
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| − | #* Provides a framework over which the leukocytes crawl to reach the irritant.
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| − | #* Fibrin is also chemotactic to neutrophils, bringing more of these cells into the injured area.
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| − | # Exudate on a suface will wash away the irritant.
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| − | #* E.g the skin and alimentary track.
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| − | # Brings the irritant to the lymph nodes, via the lymphatics, for further processing or antigen presentation.
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| − | #* Preferably within white blood cells such as macrophages and neutrophils.
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| − | #* Local lymph nodes may also be inflamed following inflammation of a tissue which drains into them.
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| − | ===Sequelae to Exudation===
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| − | * Catarrhal and serous exudationresolve when the irritant is overcome.
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| − | ** Alternatively, they may progress to a more serious reaction.
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| − | * Fibrinous exudates may also resolve if the fibrin is digested by macrophages.
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| − | ** In the pleural and peritoneal cavities, the fibrin may become rganised into fibrous tissue, producing adhesions between the visceral surface.
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| − | * Diphtheritic inflammation will only repair by scar formation.
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| − | * If haemorrhagic lesions are widespread, they most commonly associated with acute deaths.
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| − | ** For example in acute viral, bacterial or toxic diseases.
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| − | * If the exudation is strictly localised, for example in brusing, then repair may occur.
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| − | * The resolution of abscesses depends upon their location.
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| − | ** If the abscess is near to a surface it will rupture onto it.
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| − | ** This is beneficial in the skin where it discharges to the exterior, hopefully getting rid of the pyogenic organism.
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| − | ** If the abscess is in deeper tissues, there is extensive fibrous capsule formation.
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| − | *** The fluid becomes inspissated due to withdrawal of water content.
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| − | *** Macrophages digest the necrotic remains.
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| − | *** Fibrous tissue organises the interior.
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| − | *** The very end result is a fibrous scar.
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| − | ==Cells==
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| − | * The classical cells of acute inflammation are [[Neutrophils|neutrophils]], [[Eosinophils|eosinophils]], [[Macrophages|macrophages]], [[Mast Cells|mast cells]] and [[Basophils|basophils]].
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| − | ** [[Macrophages|Macrophages]] are a common feature of acute and chronic inflammation.
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| | [[Category:Inflammation]] | | [[Category:Inflammation]] |