Makindo Medical Notes

Related Subjects: | Acute Inflammation

🔥 Acute inflammation is a rapid, early defensive response of the body to harmful stimuli such as pathogens, damaged cells, or irritants. It is characterised by the classical signs of ➡️ heat, redness, swelling, pain, and loss of function. Its main purposes are to eliminate the cause of injury, remove necrotic debris, and initiate tissue repair.

🔄 Stages of Acute Inflammation

• 1. Initiation 🛎️ :
  • Recognition of harmful stimuli via pattern recognition receptors (PRRs) on immune cells.
  • Release of inflammatory mediators such as histamine, prostaglandins, cytokines.
• 2. Vascular Changes 💉 :
  • Vasodilation: Increased blood flow → redness & heat.
  • Increased vascular permeability: Plasma proteins & fluid leak into tissues → oedema (swelling).
• 3. Cellular Events 🧑‍⚕️🦠 :
  • Leukocyte recruitment: Margination → rolling → adhesion → transmigration (diapedesis).
  • Phagocytosis: Neutrophils & macrophages engulf debris → fuse phagosome with lysosome → destruction by ROS & enzymes.

🧪 Chemical Mediators of Inflammation

• Vasoactive Amines ⚡ :
  • Histamine: Mast cells, basophils, platelets → vasodilation & permeability.
  • Serotonin: Platelets & enterochromaffin cells → similar vascular effects.
• Plasma Protein Systems 🩸 :
  • Complement (C3a, C5a): Anaphylatoxins → permeability & chemotaxis. C3b acts as an opsonin.
  • Coagulation: Fibrin meshwork forms a clot scaffold.
  • Kinin system: Bradykinin → vasodilation, pain, permeability.
• Arachidonic Acid Metabolites 🌀 :
  • Prostaglandins (COX): Pain, vasodilation, fever.
  • Leukotrienes (LOX): Chemotaxis, permeability, bronchospasm.
• Cytokines & Chemokines 📢 :
  • TNF, IL-1: Fever, adhesion molecules, systemic acute phase response.
  • Chemokines: Recruit leukocytes to the site.
• ROS & Nitric Oxide ⚔️ :
  • Microbicidal and signalling roles.
  • Excess = tissue injury (ARDS, reperfusion injury).

🧭 Outcomes of Acute Inflammation

• ✅ Resolution: Full clearance & return to normal tissue.
• 💥 Abscess: Localised pus collection when clearance fails.
• ♻️ Chronic inflammation: If stimulus persists → fibrosis & immune activation.
• 🧱 Fibrosis/scarring: When tissue repair is incomplete.

🩺 Clinical Signs & Symptoms ("Cardinal Signs")

• 🔴 Redness (Rubor): Vasodilation, hyperaemia.
• 🔥 Heat (Calor): Increased blood flow & metabolic activity.
• 💧 Swelling (Tumour): Oedema from plasma leakage.
• 😣 Pain (Dolor): Mediated by bradykinin, prostaglandins, pressure effects.
• ⚠️ Loss of Function (Functio Laesa): Pain & swelling limiting use.

📚 Clinical Relevance

• Fever in systemic inflammation is driven by IL-1 & TNF acting on the hypothalamus.
• Raised CRP & ESR are acute phase reactants produced by the liver.
• Uncontrolled acute inflammation can → sepsis, SIRS, or chronic inflammation (e.g. Crohn’s, RA).

📝 Summary

Acute inflammation is an essential protective response, aimed at eliminating harmful agents and initiating repair. It integrates vascular changes, leukocyte activity, and chemical mediators. ⚖️ While vital, if unchecked it can cause collateral tissue injury or evolve into chronic disease.