Inflammation

Inflammation is the response of living tissue to damage. The acute inflammatory response has 3 main functions.

The affected area is occupied by a transient material called the acute inflammatory exudate. The exudate carries proteins, fluid and cells from local blood vessels into the damaged area to mediate local defenses.

If an infective causitive agent (e.g. bacteria) is present in the damaged area, it can be destroyed and eliminated by components of the exudate.

The damaged tissue can be broken down and partialy liquefied, and the debris removed from the site of damage.

The cause of acute inflammation may be due to physical damage, chemical substances, micro-organisms or other agents. The inflammatory response consist of changes in blood flow, increased permeability of blood vessels and escape of cells from the blood into the tissues. The changes are essentially the same whatever the cause and wherever the site.

Acute inflammation is short-lasting, lasting only a few days. If it is longer lasting however, then it is referred to as chronic inflammation. Various examples of acute inflammation that you may be aware of are sore throat, reactions in the skin to a scratch or a burn or insect bite, and acute hepatitis and so on. However, there are occasional historical exceptions such as pneumonia, inflammation of the lung rather than pneumonitis and pleurisy, inflammation of the pleura, rather than pleuritis.

Microbial infections

One of the commonest causes of inflammation is microbial infection. Viruses lead to death of individual cells by intracellular multiplication . Bacteria release specific exotoxins - chemicals synthesised by them which specifically initiate inflammationÑor endotoxins, which are associated with their cell walls. Additionally, some organisms cause immunologically-mediated inflammation through hypersensitivity reactions. Parasitic infections and tuberculous inflammation are instances where hypersensitivity is important.

Hypersensitivity reactions

A hypersensitivity reaction occurs when an altered state of immunological responsiveness causes an inappropriate or excessive immune reaction which damages the tissues. The types of reaction are classified here, but all have cellular or chemical mediators similar to those involved in inflammation.

Physical agents

Tissue damage leading to inflammation may occur through physical trauma, ultraviolet or other ionising radiation, burns or excessive cooling ('frostbite').

Irritant and corrosive chemicals

Corrosive chemicals (acids, alkalis, oxidising agents) provoke inflammation through gross tissue damage. However, infecting agents may release specific chemical irritants which lead directly to inflammation.

Tissue necrosis

Death of tissues from lack of oxygen or nutrients resulting from inadequate blood flow (infarction) is a potent inflammatory stimulus. The edge of a recent infarct often shows an acute inflammatory response.