Inflammation: causes and classification

Inflammation: causes and classification


Inflammation is a local response (reaction) of living vasculaized tissues to endogenous and exogenous stimuli. The term is derived from the Latin “inflammare” meaning to burn. Inflammation is fundamentally destined to localize and eliminate the causative agent and to limit tissue injury.
Thus, inflammation is a physiologic (protective) response to injury, an observation made by Sir John Hunter in 1794 concluded: “inflammation is itself not to be considered as a disease but as a salutary operation consequent either to some violence or to some diseases”.


 Causes of inflammation are apparently causes of diseases such as

Physical agents: mechanical injuries, alteration in temperatures and pressure, radiation injuries.

Chemical agents: including the ever increasing lists of drugs and toxins.

Biologic agents (infectious): bacteria, viruses, fungi, parasites

Immunologic disorders: hypersensitivity reactions, autoimmunity, immunodeficiency states etc

Genetic/metabolic disorders: examples gout, diabetes mellitus etc…


The nomenclatures of inflammatory lesion are usually indicated by the suffix ‘itis’. Thus, inflammation of the appendix is called appendicitis and that of meninges as meningitis, etc.… However, like any rule, it has its own exceptions examples pneumonia, typhoid fever, etc….


Inflammation is classified crudely based on duration of the lesion and histologic appearances into acute and chronic inflammation.

Acute inflammation

Acute inflammation is an immediate and early response to an injurious agent and it is relatively of short duration, lasting for minutes, several hours or few days. It is characterized by exudation of fluids and plasma proteins and the emigration of predominantly neutrophilic leucocytes to the site of injury.

The five cardinal signs of acute inflammation are:

 Redness (rubor) which is due to dilation of small blood vessels within damaged tissue as it occurs in cellulitis.

Heat (calor) which results from increased blood flow (hyperemia) due to regional-vascular dilation

Swelling (tumor) which is due to accumulation of fluid in the extravascular space which, in turn, is due to increased vascular permeability.

Pain (dolor), which partly results from the stretching & destruction of tissues due to inflammatory edema and in part from pus under pressure in as abscess cavity. Some chemicals of acute inflammation, including bradykinins, prostaglandins and serotonin are also known to induce pain.

Loss of function: The inflammed area is inhibited by pain while severe swelling may also physically immobilize the tissue

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