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• Inflammation is a dynamic process
• Occurs in response to tissue injury
• Causes of inflammation include:
  • Physical injury
  • Chemical injury
  • Infection
  • Immunological disorders
• Inflammation can be acute or chronic
• Different mechanisms involved in the two processes

Acute inflammation

• Classic signs of acute inflammation are:
  • Redness - rubor
  • Heat - calor
  • Swelling - tumor
  • Pain - dolor
  • Loss of function
• Clinical features can be explained by changes at microscopic level
• Three features are seen:
  • Hyperaemia
  • Exudation
  • Emigration of leukocytes

Hyperaemia

• Hyperaemia is associated with vascular response
• Initial vasoconstriction occurs
• Followed by arteriolar dilatation
• Occurs due to:
  • Direct vascular injury
  • Chemical mediators causing vasodilatation
  • Autonomic neurological response
• Explains the redness and heat

Exudation

• Passage of protein rich fluid into interstitial tissue
• Results in protective antibodies entering the damaged tissue
• Occurs as a result of:
  • Increased capillary permeability
  • Increased capillary pressure
  • Increased tissue oncotic pressure
• Explains the swelling

Emigration of leukocytes

• Increased blood viscosity reduces capillary blood flow
• Loss of axial stream results in margination of polymorphs
• Polymorphs and mononuclear cells adhere to endothelium
• Pass between endothelial cells into interstitum
• Process facilitated by chemotaxis

Sequels of acute inflammation

• There are four possible outcomes of acute inflammation
  • Resolution
  • Suppuration
  • Repair and organisation
  • Chronic inflammation

Resolution

• Resolution is the restoration of normal conditions
• Occurs if
  • Minimal cell death and tissue damage
  • Rapid elimination of causal agent
  • Local conditions favour removal of fluid and debris

Suppuration

• Suppuration is the formation of pus
• Pus is formed by the inflammatory exudate, polymorphs and cell fragments
• If pus accumulates an abscess may form
• Pyogenic bacteria are the usual cause

Organisation

• Organisation occurs when during the acute inflammatory process
  • There is excessive exudation or necrosis
  • Local conditions prevent removal of exudate or debris
• New vessel formation occurs
• Macrophage and fibroblast proliferation results in fibrosis

Chronic inflammation

• Chronic inflammation occurs if the causal agent is not removed
• Cell population in the damaged tissue changes
• Polymorphs are replaced by lymphocytes and plasma cells
• Macrophages may form giant cells
• New capillaries are formed
• Fibroblasts deposit collagen and result in fibrosis
• Chronic inflammation can be primary with no prior acute inflammatory response
• Occurs in tuberculosis and sarcoidosis
• Characterised by the formation of granulomas

Author:  Dr Shakeeb Khan

Last updated: 05 January 2008

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