Inflammation
- 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
|
Last modified:
|