Inflammation: Causes and Terminology

Definition of Inflammation

• Inflammation is a vascularized living tissue's reaction to injury
• The term "inflammation" stems from the Latin word "inflammare," meaning "setting something on fire"

Nomenclature of Inflammation

• Inflammation of a specific organ or tissue is usually indicated by the suffix "-itis" attached to the organ's Latin name
• Examples include "dermatitis" for inflammation of the skin and "hepatitis" for inflammation of the liver
• The suffix "-itis" generally signifies "diseases characterized by inflammation"
• Some inflammation terms don't end in "-itis," such as "pleurisy" (inflammation of the pleura) and "pneumonia" (inflammation of the lung)

Causes of Inflammation

• Causes are numerous and diverse, including:
  • Infectious agents: bacteria, viruses, fungi, and parasites
  • Physical irritants: excessive heat, cold, ionizing radiation, heatstroke
  • Chemical irritants: caustic agents, poisons, venom
  • Nutritive irritants: ischemia, vitamin deficiencies
  • Endogenous causes: hypersensitivity and autoimmune reactions

Functions of Inflammation

• Inflammation is often a protective mechanism with the following primary purposes:
  • Dilute, isolate, and eliminate the causative agent
  • Repair tissue damage caused by the injury

Classification of Inflammation

• Inflammation can be categorized according to:
  • Distribution (Location within an organ)
    • Focal: A single inflamed area within a tissue, ranging in size from 1 mm to several centimeters
    • Multifocal: Several foci separated by relatively normal tissue, with variable size
    • Locally Extensive (Focally Extensive): Significant involvement of an area within an organ
    • Diffuse Inflammation: Involves all tissue or an entire organ
  • Severity (How severe is the process?): Mild, Moderate, or Severe
  • Duration (How long does it persist?):
    • Peracute Inflammation: Characterized by a very short course, caused by potent stimuli like African swine fever, clostridial infection, avian influenza, African horse sickness, and anthrax. Lesions include hyperemia, slight edema, hemorrhage, and few inflammatory cells.
    • Acute Inflammation: A short-term process (hours to days) appearing rapidly after exposure to the causative agent. Progresses to either resolution or chronic inflammation.
      • Gross Lesions: Cardinal signs of inflammation
        • Redness (Rubor)
        • Hotness (Calor)
        • Swelling (Tumor)
        • Pain (Dolor)
        • Loss of function (Functiolaesa)
      • Microscopic Lesions:
        • Vascular Congestion: Distension of blood vessels with blood
        • Leukocytic Infiltration: Migration of blood leukocytes to the extravascular tissue (leukocyte margination, rolling, adhesion, and transendothelial cell migration)
        • Presence of Exudate (Inflammatory Fluid)
          • Types of Acute Inflammation based on Exudate Character:
            • Serous Inflammation: Clear to slightly yellow, watery fluid within the tissue, possibly forming raised fluid-filled vesicles
            • Catarrhal Inflammation: Inflammation of mucous membranes in digestive, respiratory, and urogenital tracts. Grossly, it appears covered or contains mucous. Microscopically, hyperemia, leukocytic infiltration, and mucin are present.
            • Purulent (Suppurative) Inflammation: Caused primarily by pyogenic bacteria. Characterized by the production of pus, which can vary in consistency and color depending on the causative agent and species.
            • Hemorrhagic Inflammation: Due to severe irritants causing vascular injury and an exudate rich in erythrocytes
            • Fibrinous Inflammation: Exudation of fibrin-rich fluid due to severe irritants that damage endothelial cells and allow leakage of large proteins like fibrinogen, which polymerizes into fibrin in the extracellular space.

Chronic Inflammation

• Chronic Inflammation: Inflammation of prolonged duration (weeks, months, or years) marked by chronic inflammatory cell infiltration and fibroplasia.

• Causes:

  • Failure of the acute inflammatory response to eliminate the causative agent
  • Repeated episodes of acute inflammation
  • Unique properties of the causative agent

• Gross Picture:

  • Grey to white color due to macrophage and lymphocyte infiltrates, fibroblast proliferation, and fibrous connective tissue deposition
  • Firm consistency due to fibroblast proliferation, fibrous connective tissue deposition, and exudate solidification
  • Irregular shape due to:
    • Haphazard accumulation of leukocytes
    • Fibrosis
    • Contraction of the lesion by myofibroblasts within the fibrous connective tissue

• Microscopic Picture:

  • Chronic Inflammatory Cell Infiltrate: Lymphocytes, macrophages, plasma cells, epithelioid cells, and sometimes multinucleate giant cells
  • Fibroplasia: Proliferation of fibroblasts and collagen deposition

Inflammatory Cells

• Acute Inflammatory Cells

  • Neutrophils: The first leukocytes recruited to the inflammatory exudate, prominent in suppurative inflammations
  • Mast Cells: Initiate acute inflammatory responses
  • Eosinophils: Crucial role in allergic and parasitic diseases
  • Basophils: Important role in allergic diseases

• Chronic Inflammatory Cells

  • Macrophages:
  • Epithelioid Cells: Larger than activated macrophages with abundant cytoplasm but diminished phagocytic capacity. Their physiological activity remains unclear.

This quiz explores the definition, nomenclature, and causes of inflammation. Learn about the various forms of inflammation and their linguistic roots. Test your knowledge of terms like '-itis' and the factors leading to inflammation.