Acute Inflammation: Body Defense Reaction

Acute Inflammation

• Definition: Local response of living tissues to injury due to any agent, aiming to eliminate or limit the spread of injurious agents and remove necrosed cells and tissues.

Inflammation Process

• Involves 2 basic processes: inflammatory response and healing process
• Complex host response for survival, involving host cells, blood vessels, proteins, and other mediators

Types of Inflammation

• Acute inflammation: short duration (minutes, hours, few days), represents the early body reaction, usually followed by repair
• Chronic inflammation: prolonged duration

Signs of Acute Inflammation

• Redness (rubor)
• Swelling (tumor)
• Heat (calor)
• Pain (dolor)
• Loss of function

Acute Inflammation Changes

• Vascular events: accumulation of fluid exudate and neutrophils in tissues, controlled by chemical mediators
• Cellular changes: margination, rolling, emigration, transmigration, chemotaxis, activation, and phagocytosis

Causes of Acute Inflammation

• Microbial infections
• Hypersensitivity reactions
• Physical agents
• Chemicals
• Tissue necrosis

Steps of Acute Inflammation

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

Vascular Changes

• Vasodilation: increase in blood flow and permeability
• Edema formation: increased permeability of blood vessels, leading to exudation of protein-rich fluid into tissues

Cellular Changes

• Margination and rolling: neutrophils lining up and rolling along the endothelium
• Emigration: neutrophils migrating through the blood vessel wall
• Chemotaxis and phagocytosis: neutrophils migrating to the site of injury, phagocytosing microorganisms, and releasing toxic metabolites and enzymes

Exudate vs Transudate

• Exudate: fluid loss in inflammation, high protein content, specific gravity above 1.02
• Transudate: fluid loss due to hydrostatic pressure imbalance, low protein content, specific gravity less than 1.012

Oedema

• Excess of fluid in interstitium, can be transudate or exudate
• Leads to increased lymphatic drainage
• Pus: a purulent exudate, rich in neutrophils and cell debris

Hallmark of Acute Inflammation

• Exudate (of fluid): delivers plasma proteins, immunoglobulins, inflammatory mediators, and fibrinogen to the area of injury, dilutes toxins, and increases lymphatic drainage
• Infiltrate (of cells): removes pathogenic organisms, necrotic debris, and delivers microorganisms to phagocytes and antigens to the immune system