Overview of Inflammation

Inflammation Overview

• Inflammation is a defensive response to foreign invaders and necrotic tissue.
• Key components are vascular reaction and cellular response, both activated by mediators from plasma proteins and cells.
• Inflammation's purpose is to dilute, destroy, or neutralize harmful agents (microbes, toxins).
• Inflammation and the repair process can cause harm.
• The goal of the inflammatory response is to bring defense cells and molecules to the site of infection or tissue damage.

Steps of the Inflammatory Response (Five Rs)

• Recognition of the injurious agent.
• Recruitment of leukocytes.
• Removal of the agent.
• Regulation (control) of the response.
• Resolution (repair).

Outcomes of Acute Inflammation

• Elimination of the harmful stimulus, followed by repair of the damaged tissue.
• Persistent injury resulting in chronic inflammation.

Acute Inflammation Characteristics

• Rapid onset and short duration.
• Characterized by fluid and plasma protein exudation and a predominantly neutrophilic leukocyte accumulation.

Two Major Components of Acute Inflammation

• Vascular changes:

  • Vasodilation: Increased blood vessel caliber leading to increased blood flow.
  • Increased vascular permeability: Changes in vessel walls that allow plasma proteins to leave the circulation.

• Cellular events:

  • Cellular recruitment: Leukocytes move from the circulation to the site of injury.
  • Activation of leukocytes: Enabling them to eliminate the offending agent.
  • Principal leukocytes during acute inflammation are neutrophils (polymorphonuclear leukocytes).

Stimuli for Acute Inflammation

• Infections (bacterial, viral, fungal, parasitic).
• Trauma and various physical and chemical agents (thermal injury, irradiation, toxicity).
• Tissue necrosis (physical, chemical).
• Foreign bodies (splinters, dirt, sutures, crystal deposits).
• Immune reactions (hypersensitivity reactions) against environmental substances or "self" tissues.

Cardinal Signs of Inflammation

• Redness: Caused by dilated blood vessels in the affected area.
• Heat: Caused by increased blood flow to the area, felt in peripheral areas (skin).
• Swelling (edema): Caused by fluid buildup outside blood vessels.
• Pain: Caused by chemical mediators and tissue distortion from edema.
• Loss of function: Affected body part may not function normally.

Chronic Inflammation

• Prolonged duration (weeks to years).
• Continuing inflammation, tissue injury, and healing (often by fibrosis) proceed simultaneously.

Chronic Inflammation Characteristics

• Infiltration with mononuclear cells (macrophages, lymphocytes, plasma cells).
• Tissue destruction, mainly from inflammatory cell products.
• Repair involving new vessel proliferation (angiogenesis) and fibrosis.

Chronic Inflammation Settings

• Persistent infections by microbes (difficult to eradicate).
• Immune-mediated inflammatory diseases (rheumatoid arthritis, inflammatory bowel disease, psoriasis).
• Prolonged exposure to potentially toxic agents (nondegradable exogenous materials like inhaled silica).

Granulomatous Inflammation

• Distinctive pattern of chronic inflammation characterized by aggregates of activated macrophages.

Granuloma Formation

• Formation under 3 settings:
  • Persistent T-cell responses to certain microbes (tuberculosis).
  • Immune-mediated inflammatory diseases (Crohn's disease).
  • Foreign bodies (sutures, splinters) - foreign body granulomas.
• Granulomas also seen in sarcoidosis (a disease of unknown etiology).