Acute inflammation is the immediate and early response of the body to injury or infection, forming a key part of the innate immune system. It aims to eliminate the cause of injury, remove dead cells, and initiate tissue repair.
Key Characteristics
| Feature | Description |
|---|---|
| Onset | Rapid (seconds to minutes) |
| Duration | Short (minutes to a few days) |
| Predominant Cells | Neutrophils (first responders) |
| Purpose | Remove injurious agents and necrotic tissue; begin repair |
| Outcome | Resolution, abscess formation, or chronic inflammation |
Cardinal Signs of Inflammation
These are the classical features described by Celsus and Virchow:
| Latin Term | Meaning | Physiological Basis |
|---|---|---|
| Rubor | Redness | Vasodilation → ↑ blood flow |
| Calor | Heat | Vasodilation + increased metabolism |
| Tumor | Swelling | Increased vascular permeability → edema |
| Dolor | Pain | Stimulation of nerve endings by bradykinin, PGE₂, etc. |
| Functio laesa | Loss of function | Due to pain and swelling interfering with function |
Major Components of Acute Inflammation
- Hemodynamic Changes
- Vasodilation (mediated by histamine, nitric oxide) → ↑ blood flow
- Increased vascular permeability → leakage of plasma proteins → edema
- Stasis and margination → leukocytes move toward the endothelium
- Cellular Component – Neutrophils
- First cells to arrive at the site of injury (within 6–24 hours)
- Functions:
- Phagocytosis of microbes and debris
- Release of enzymes and reactive oxygen species (ROS)
- Secretion of cytokines to amplify inflammation
- Chemical Mediators
Mediator Source Function Histamine Mast cells, basophils Vasodilation, ↑ permeability Prostaglandins Arachidonic acid pathway Pain, fever, vasodilation Leukotrienes Leukocytes Chemotaxis, vascular permeability Cytokines (IL-1, TNF) Macrophages, endothelium Fever, leukocyte activation Complement system Plasma proteins Opsonization, cell lysis, chemotaxis Bradykinin Plasma (kinin system) Pain, vasodilation, permeability
Key Points to Remember
- Acute inflammation is a protective response; however, excessive or prolonged inflammation can lead to tissue damage.
- Neutrophils dominate early inflammation; macrophages and lymphocytes appear later, typically in a chronic setting.
- Resolution occurs when the injurious agent is removed, and tissue repair begins.
Learning Objective
By the end of this topic, the student should be able to:
- Describe the key features, cellular and vascular events, and mediators involved in acute inflammation, and correlate these with the classical clinical signs.
