Learning Objectives
Define the primary goals of the Inflammatory Response and distinguish between its protective and harmful effects. Master the Cardinal Signs of inflammation, their underlying biochemical mediators, and the systemic Acute-Phase Reaction involving fever and leukocytosis.
1. The Purpose and Risk of Inflammation
Inflammation is a protective response designed to eliminate the initial cause of cell injury, remove necrotic debris, and initiate tissue repair. However, it is a double-edged sword; if excessive or inappropriate, it can lead to significant host tissue damage.
| Response Level | Clinical Examples of Harm |
|---|---|
| Excessive | Septic Shock (systemic cytokine storm). |
| Prolonged | Persistent infections like Tuberculosis (TB). |
| Inappropriate | Autoimmune diseases such as SLE or Rheumatoid Arthritis. |
2. Cardinal Signs of Inflammation
The local clinical manifestations of acute inflammation are driven by changes in vascular flow, permeability, and nerve sensitization.
| Sign | Mechanism | Primary Mediators |
|---|---|---|
| Rubor & Calor | Arteriolar vasodilation → ↑ blood flow. | Histamine, Prostaglandins, Bradykinin, NO. |
| Tumor (Swelling) | Endothelial contraction → ↑ vascular permeability → Exudate. | Leukotrienes (C4, D4, E4), Histamine. |
| Dolor (Pain) | Sensitization of sensory nerve endings. | Bradykinin, PGE2. |
| Functio Laesa | Impaired function due to pain/swelling. | Physical constraint (e.g., hand cellulitis). |
Activity:
3. Systemic Manifestations (Acute-Phase Response)
Inflammation is not just local; cytokines released by macrophages coordinate a whole-body response.
| Manifestation | Pathway / Mediator | Effect |
|---|---|---|
| Fever | Macrophages (IL-1, TNF) → Hypothalamus → PGE2. | Elevates hypothalamic temperature set point. |
| Leukocytosis | Cytokine-driven release of WBCs from bone marrow. | ↑ Neutrophils (bacteria) or Lymphocytes (viruses). |
| Acute-Phase Reactants | Primarily induced by IL-6. | Liver produces CRP, Fibrinogen, Hepcidin, etc. |
Activity
High-Yield Mnemonics & Tips:
- Pain Mediators: Remember Bradykinin and PGE2 cause Bad Pain.
- Fever Mechanism: Pyrogens increase COX activity in the hypothalamus. This is why NSAIDs (which inhibit COX) are effective at reducing fever.
- Vascular Permeability: Occurs specifically at the postcapillary venules. Leakage of protein-rich fluid is called an exudate.