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inflammation

inflammation The word incorporates the Greek for flame, and indeed an inflamed body part may feel ‘on fire’. In its traditional clinical description, inflammation has four characteristics: calor (heat), rubor (redness), tumor (swelling and dolor (pain). They are the manifestations of the body's defence against injury or against invasion by foreign material or microorganisms, including the means of removal or destruction of the offending agent, restriction of the spread of infection, and preparations for the healing process. But the immune system that implements vital self-preservation may also sometimes cause inflammation by misdirected attack on some part of the body itself.

Inflammation can occur anywhere, acutely in the skin around a wound or a sting, or in less visible sites such as the lining of the middle ear, or of the bladder, or of the gall bladder. Chronically it can be related to persistent infection, ulceration, mechanical or chemical irritation, or autoimmune disease. Wherever inflammation occurs there are certain local mechanisms in common, despite differences in the precipitating factors and also in the relative prominence of the four cardinal features. Even with relatively minor and apparently localized problems, there are whole-body responses. Wherever inflammation is located, the condition is given a name ending in-itis, prefixed by the traditional name of the body part, such as arthritis for the joints, gastritis for the stomach, pericarditis for the membranes around the heart, ileitis for the small intestine, osteitis for bone, encephalitis for the brain.

Tissue damage results in the release by cells of various chemical agents, including prostaglandins. Vasodilator substances relax the blood vessels in their vicinity and the resulting increase in blood flow accounts for the redness and heat; swelling follows from increased permeability of blood vessels. This all enhances the supply of factors normally present in the blood that are important for the inflammatory response, including white blood cells and certain proteins in the plasma. Locally released substances (cytokines), as well as bacterial toxins if there is infection, attract cells of the immune system — macrophages and lymphocytes.

The nerves that carry the signals, set up by chemical and mechanical stimulation of sensory receptors, that we perceive as pain, themselves in turn promote an increase in local blood flow through the axon reflex mechanism. The nerve fibres (axons) give off branches back to their site of origin, and these release ‘substance P’, a peptide that relaxes the vessel walls. This, together with prostaglandins and other substances released from damaged tissues and also from the macrophages that congregate at the site, increases the sensitivity of sensory nerve endings, enhancing pain.

The events are not confined to the focus of trouble. Cytokines circulating in the blood provoke diverse whole-body responses. A major site of action is the hypothalamus, where they can affect its regulation of pituitary secretions, of sympathetic nervous system activity, and of body temperature. Whilst the resulting responses mainly promote the many aspects of defence, some also modify reactions that might otherwise be excessive: endorphin release modifies pain, and the increase in secretion of corticosteroids has anti-inflammatory effects, including toning down the activity of macrophages and interfering with prostaglandin synthesis.

The manifestations of inflammation vary greatly with the nature and severity of the insult and whether the process is rapidly or slowly developing. It can be simply serous, with fluid exudation, such as in a blister or a swollen joint, or in the rhinitis (of the nose) at the start of a common cold. With some types of infection it can be suppurative, where tissue and immune cell debris form a collection of pus; and chronic inflammation can be granulomatous, with nodules composed of packed inflammatory cells.

The phenomena of inflammation reflect an appropriate response to infection, or to mechanical damage either by acute injury or prolonged pressure or friction. When they occur inappropriately as a reaction against the body's own tissues the manifestations are similar. Thus conditions that might be called ‘inflammatory’ may refer to chronic infections, or to degenerative processes (as in osteoarthritis), or they may result from congenital abnormalities (as in cystic fibrosis) or autoimmune disease (such as rheumatoid arthritis or regional ileitis (Crohn's disease)).

It would be inappropriate to attempt by treatment to diminish the body's responses, in terms of both local and widespread effects, if and when they were entirely appropriate and necessary to contain or cure the condition. Alleviation of the pain of inflammation by analgesic drugs is clearly beneficial to the sufferer; otherwise the first concern of treatment is if possible to remove the cause (such as treating infection by antibiotics, or removing foreign material). Other treatments in recent decades have been directed against inflammation itself, in conditions related to injury, ‘wear-and-tear’, and auto-immunity. Imitation and enhancement of the body's own anti-inflammatory corticosteroids became possible with synthetic steroid preparations, but there are undesirable side-effects. Along with the understanding of the role of prostaglandins in the mediation of inflammation and fever, a whole family of ‘non-steroidal antiflammatory drugs’ (NSAIDS) were developed, and they are widely used for a variety of muscle and joint problems, from accidental sprains to widespread arthritis. These drugs inhibit enzymes necessary for formation of prostaglandins, thus diminishing their local and general effects. (aspirin was well known to be useful in this context long before it was known to act by this mechanism.) No evidence has emerged for any positive or negative effect on the progress of the underlying conditions themselves (as opposed to relief of the symptoms), supporting the notion that the body's inflammatory responses are not always useful. Symptoms may indeed be relieved, but there are side-effects of NSAIDS, particularly gastrointestinal complications, related to the inhibition of prostaglandin synthesis where and when it is normally needed.

Sheila Jennett


See also autoimmune diseases; fever; immune system; infection; infectious diseases; injury; pain; prostaglandins.

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Inflammation

Inflammation

Inflammation is a localized, defensive response of the body to injury, usually characterized by pain, redness, heat, swelling, and, depending on the extent of trauma, loss of function. The process of inflammation, called the inflammatory response, is a series of events, or stages, that the body performs to attain homeostasis (the body's effort to maintain stability). The body's inflammatory response mechanism serves to confine, weaken, destroy, and remove bacteria , toxins, and foreign material at the site of trauma or injury. As a result, the spread of invading substances is halted, and the injured area is prepared for regeneration or repair. Inflammation is a nonspecific defense mechanism; the body's physiological response to a superficial cut is much the same as with a burn or a bacterial infection . The inflammatory response protects the body against a variety of invading pathogens and foreign matter, and should not be confused with an immune response, which reacts to specific invading agents. Inflammation is described as acute or chronic, depending on how long it lasts.

Within minutes after the body's physical barriers, the skin and mucous membranes, are injured or traumatized (for example, by bacteria and other microorganisms , extreme heat or cold, and chemicals), the arterioles and capillaries dilate, allowing more blood to flow to the injured area. When the blood vessels dilate, they become more permeable, allowing plasma and circulating defensive substances such as antibodies, phagocytes (cells that ingest microbes and foreign substances), and fibrinogen (blood-clotting chemical) to pass through the vessel wall to the site of the injury. The blood flow to the area decreases and the circulating phagocytes attach to and digest the invading pathogens. Unless the body's defense system is compromised by a preexisting disease or a weakened condition, healing takes place. Treatment of inflammation depends on the cause. Anti-inflammatory drugs such as aspirin, acetaminophen, ibuprofen, or a group of drugs known as NSAIDs (non-steroidal anti-inflammatory drugs) are sometimes taken to counteract some of the symptoms of inflammation.

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inflammation

inflammation, reaction of the body to injury or to infectious, allergic, or chemical irritation. The symptoms are redness, swelling, heat, and pain resulting from dilation of the blood vessels in the affected part with loss of plasma and leucocytes (white blood cells) into the tissues. White blood cells communicate with each other via cytokines, which are polypeptides released by cells of the immune system that regulate other cells. They are a broad class of soluble compounds that signal one cell type to another, particularly in response to foreign substances. Granulomas are most common in infectious diseases such as tuberculosis, leishmaniasis, and schistosomiasis, in which the body's defenses, unable to destroy the offending organisms, try to enclose them in a mass of inflammatory cells. Certain types of inflammation result in pus formation, as in an abscess. The leukocytes destroy harmful microorganisms and dead cells, preventing the spread of the irritation and permitting the injured tissue to repair itself.

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inflammation

inflammation The defence reaction of tissue to injury, infection, or irritation by chemicals or physical agents. Cells in the affected tissue release various substances, including histamine, serotonin, kinins, and prostaglandins. These cause localized dilatation of blood vessels so that fluid leaks out and blood flow is increased. They also attract white blood cells (lymphocytes) to the site. Overall, these responses lead to swelling, redness, heat, and often pain. White blood cells, particularly phagocytes, enter the tissue and an immune response is stimulated. A gradual healing process usually follows.

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inflammation

inflammation (in-flă-may-shŏn) n. the body's response to injury. acute i. the immediate defensive reaction of tissue to injury, which may be caused by infection, chemicals, or physical agents. It involves pain, heat, redness, swelling, and loss of function of the affected part. chronic i. the response that ensues when acute inflammation does not heal.
inflammatory (in-flam-ă-ter-i) adj.

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inflammation

inflammation Reaction of body tissue to infection or injury, with resulting pain, heat, swelling and redness. It occurs when damaged cells release histamine, which causes blood vessels at the damaged site to dilate. Leucocytes invade the area to engulf bacteria. Macrophages remove dead tissue, sometimes with the formation of pus.

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inflammation

in·flam·ma·tion / ˌinfləˈmāshən/ • n. a localized physical condition in which part of the body becomes reddened, swollen, hot, and often painful, esp. as a reaction to injury or infection: chronic inflammation of the nasal cavities.

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