Inflammation: Types and Characteristics

Inflammation Definition

• Inflammation is a protective response of the body to tissue injury.
• It involves vascularized connective tissue.
• The process aims to eliminate the injurious agent, localize the damage, remove necrotic tissue, and repair the injured tissue.
• There are two main types of inflammation: acute and chronic.

### Acute Inflammation

• Characterized by exudation (fluid leakage) and neutrophil emigration.
• It is an immediate or early response to injury.
• The duration is short (minutes, hours, or a few days).
• It represents the early body reaction to injury.
• Acute inflammation is usually followed by tissue repair.

Chronic Inflammation

• Characterized by tissue damage and the presence of lymphocytes, macrophages, new blood vessels, and connective tissue proliferation.
• It develops slowly and persists for a longer duration.
• It is often insidious in onset.

### Subacute Inflammation

• A transitional stage between acute and chronic inflammation.

### Clinical Manifestations of Inflammation

• Cardinal Signs (Five Signs of Inflammation)
  • Redness (rubor)
  • Swelling (tumor)
  • Heat (calor)
  • Pain (dolor)
  • Loss of function

### Cellular Events

• Leukocytes extravasation and phagocytosis
  • Leukocytes are essential for eliminating the injurious agent, digesting necrotic tissue, and promoting tissue repair.
  • They can also contribute to inflammation and tissue damage through the release of enzymes, chemical mediators, and toxic oxygen species.
• Three phases of leukocytes extravasation
  • Immediate Early Response (1/2 Hour)
    • Release of histamine from mast cells, basophils, and platelets.
    • Histamine triggers vascular dilation, increases vascular permeability, and causes pain.
  • Delayed Early Response (2-4 Hours)
    • Activation of arachidonic acid metabolites (prostaglandins, leukotrienes), platelet-activating factor, and complement system.
  • Late Response (4-6 Hours)
    • Leukocyte recruitment and activation.

### Chemical Mediators of Inflammation

• Vasoactive Amines
  • Histamine and serotonin.
• Plasma Proteins
  • Clotting system, kinin system, complement system.
• Arachidonic Acid Derivatives
  • Prostaglandins and leukotrienes.
• Platelet-Activating Factor (PAF)
• Cytokines
  • IL-1, IL-6, TNF-α
• Nitric Oxide (NO)
• Oxygen-Derived Free Radicals
• Lysosomal Constituents

### Functions of Chemical Mediators

• Vasodilation: Prostaglandins and nitric oxide.
• Increased Vascular Permeability: Vasoactive amines, C3a, C5a, leukotrienes, PAF.
• Chemotaxis and Leukocyte Adhesion: C5a, chemokines.
• Fever: IL-1, IL-6, TNF-α, prostaglandins.
• Pain: Prostaglandins and bradykinin.
• Tissue Damage: Lysosomal enzymes, oxygen metabolites, nitric oxide.

### Advantages of Inflammation

• Removal of harmful agents: Leukocytes phagocytose and destroy bacteria, viruses, and other foreign substances.
• Localization of injury: Fibrin formation walls off the affected area, limiting the spread of infection.
• Tissue repair and regeneration: Inflammation promotes the healing process, replacing damaged tissue with new tissue.

### Disadvantages of Inflammation

• Loss of function: Inflammation can impair the function of affected organs or tissues, especially if the inflammation is severe or chronic.
• Exudation and swelling: Fluid accumulation can obstruct hollow organs, like in the case of laryngitis.
• Increased tissue pressure: Swelling can compress blood vessels, leading to ischemia and further tissue damage.
• Inappropriate inflammation: Hypersensitivity reactions to harmless substances can cause inflammation.

### Clinical Significance

• Inflammation is a key component of many disease processes.
• Understanding the mechanisms of inflammation is crucial for diagnosing, treating, and preventing various illnesses.
• Anti-inflammatory drugs are used to control and manage inflammation in a variety of conditions.