Outcomes of Acute and Chronic Inflammation

Study Notes

Acute inflammation outcomes depend on injury characteristics:
- Nature of injury
- Severity of injury
- Tissue involved
- Host response
Outcomes usually one of three:
- Complete resolution: Damaged tissue returns to normal. Macrophages remove cellular debris, and fluid reabsorption occurs. Common in mild, short-lived injuries like a common cold, small skin blisters, and superficial wounds. Healing often results from cell regeneration or tissue stem cell activity.
- Healing by connective tissue replacement (fibrosis): Occurs with substantial tissue destruction (example: suppurative inflammation, like purulent pericarditis) or tissues incapable of regeneration (example: large area burns). Fibrous tissue replaces injured areas.

Chronic inflammation is a prolonged process (weeks to months). Ongoing inflammation, tissue damage, and healing occur simultaneously.
Causes include:
- Persistent infection by intracellular microbes (e.g.,TB, viruses)
- Hypersensitivity reactions (e.g., autoimmune diseases, allergies)
- Exposure to prolonged toxic substances (e.g., silica, lipids)
- Diseases not typically considered inflammatory (e.g., neurodegenerative disorders, metabolic syndrome)

A distinctive form of chronic inflammation. Characterized by focal accumulations of activated macrophages (granulomas).
Etiology:
- Infections (TB, leprosy, syphilis, fungal infections)
- Inflammatory disorders (Crohn's disease, temporal arteritis)
- Inorganic particles (silicosis, berylliosis)
Types of granulomas include foreign body and immune granulomas.

Systemic effects collectively called acute phase response or Systemic Inflammatory Response Syndrome (SIRS) in severe cases.
Outcomes include:
- Fever: Increased body temperature due to fever producing substances (pyrogens) stimulating prostaglandin production in the hypothalamus.
- Acute-phase proteins: Plasma proteins (mostly from the liver) produced in elevated amounts in response to inflammatory stimuli. Increased levels of proteins like C-reactive protein (CRP) and serum amyloid A (SAA).
- Leukocytosis: Increased white blood cell count, frequently with immature neutrophils (shift to the left). Common in inflammatory reactions.
- Other manifestations: Sepsis, bacterial infections, viral infections, parasites, and certain diseases can result in disturbances, such as changes in sweating, blood pressure, and other systemic symptoms.