Pathology 3

• Acute inflammation is defined as a response of vascularized tissues to infections and damaged tissues, bringing cells and molecules of host defense from circulation to the sites where they are needed to eliminate the offending agents.
• Acute inflammation is a harmful reaction but it is also a protective response and is important for survival.
• The purpose of inflammations is to limit and isolate injury, destroy the invading microorganism and inactivate toxin, prepare the tissue for healing and repair, and to regulate the response.
• The cardinal signs of acute inflammation and their corresponding morphology are listed below:
• Chronic inflammation has an aetiology, pathogenesis, and morphology.
• Inflammatory cells are a crucial part of the inflammatory process.
• Acute inflammation is a vascular and cellular response.
• Persistence of chronic inflammation can lead to sinus formation with pus, stricture/contraction of scar, obstruction, and development of cancer in scar tissue.
• Special types of chronic inflammation include chronic granulomatous inflammation.
• The outcomes of acute and chronic inflammation are different.
• Differences between acute and chronic inflammation are also listed below:
• Chemical mediators and their functions in inflammation are also listed below:
• The steps of the inflammatory response include recognition of offending agents, recruitment of leukocytes and plasma proteins, removal of the agent, regulation of the response, and resolution (repair).
• Inflammation is terminated when the causing agents are eliminated or destroyed, secreted chemical mediators are broken down or dissipated, and there are active anti-inflammatory mechanisms which serve to control the response and prevent it from causing excessive damage to the host.
• The triggering factors (aetiology) of inflammation include microbial infections, tissue necrosis, foreign bodies, immune reaction, and complications from surgery.
• During inflammation, plasma fluid goes out from circulation into surrounding tissues, this is called exudate.
• Exudate is different from a transudate which is an ultrafiltrate of blood plasma produced as a result of osmotic or hydrostatic imbalance across the vessel wall without increase in permeability.
• Chronic inflammation is of prolonged duration, has a slow onset and lasts for weeks or months or years, and may arise from acute inflammation.
• Chronic inflammation can be caused by persistent infections by microorganisms difficult to eradicate, such as mycobacteria or certain virus, fungi, prolonged exposure to potentially toxic agents either exogenous or endogenous, or hypersensitivity diseases.
• Vasoactive amines, complement systems, arachidonic acid metabolites, cytokines, PAF, Kinins, Neuropeptides are mediators of inflammation.
• Morphologic patterns of inflammation include serous inflammation, fibrinous inflammation, suppurative or purulent inflammation, and ulcers.
• Outcomes of acute inflammation can be complete resolution, regeneration, healing by connective tissue replacement (fibrosis), or progression to chronic inflammation.
• Characteristics of chronic inflammation include on going tissue damage and inflammation, and attempts at repair.
• PAF, Kinins, Neuropeptides are other mediators of inflammation.
• Mediators of inflammation can be produced by inflammatory cells, platelets, neutrophils and endothelial cells, or derived from plasma.
• Reactions of inflammation include vasodilatation, increase in vascular permeability, chemotaxis, leukocyte recruitment and activation, and tissue damage.
• Morphological features of chronic inflammation include infiltration by mononuclear cells, which include macrophages, lymphocytes and plasma cells.
• The two major components of inflammation are vascular reaction and cellular response.
• Vascular reaction involves vessels dilating to slow down blood flow with increasing permeability to allow circulating cells (inflammatory cells) and proteins to enter the damaged site.
• Cellular response involves activated leukocytes ingesting and destroying microbes etc.
• Neutrophils are a type of inflammatory cell with cytoplasmic lysosomal granules rich in proteolytic enzymes capable of breaking down micro-organisms and tissues, they are short lived, surviving only for a few hours, and the damaged area contains both viable neutrophils and dead neutrophils.
• Mediators of inflammation are substances that initiate and regulate inflammatory reactions.
• Plasma cells develop from activated B lymphocytes and produce antibodies directed against persistent antigen at the inflammatory site.
• The breakdown products of inflammation form a thick yellow fluid, pus.
• Macrophages produce cytokines to activate B cells and transform them into plasma cells.
• Acute inflammation is characterized by the exudation of fluid and plasma protein, emigration of leukocytes (neutrophils), and the cardinal signs of heat, redness, edema, and pain.
• Macrophages are also found in bone (osteoclasts).
• Mast cells are widely distributed in connective tissue, express surface receptor for Fc portion of IgE Ab, and are present in anaphylactic reactions to foods, insect venoms or drugs.
• Eosinophils are involved in immune reactions mediated by IgE (allergic reactions) and in parasitic infections.
• The three major components of acute inflammation are dilatation of small vessels, increased permeability of the microvasculature, and emigration of leukocytes from microcirculation, accumulate at the site of injury and activation to eliminate the offending agents.