Questions
3–4 questions in university exams
Difficulty
Medium
Importance
High-yield core topic for medical and allied health sciences.
Overview
Inflammation and tissue repair represent the body's fundamental defensive and restorative responses to injury or infection. Understanding these mechanisms is critical for students to grasp how pathological stimuli initiate cellular signaling, leading to either successful resolution or chronic disease states. Mastery of these processes is a cornerstone for clinical diagnostic and therapeutic knowledge.
Acute Inflammation
Acute inflammation is the immediate, short-term response to injury, characterized by vascular changes and the rapid recruitment of neutrophils to the site of infection or trauma. It aims to eliminate the initial cause of cell injury and clear out necrotic cells.
- Cardinal signs: Rubor (redness), Calor (heat), Tumor (swelling), Dolor (pain), and Functio laesa (loss of function).
- Vascular changes involve vasodilation and increased vascular permeability.
- Predominant leukocyte is the neutrophil.
- Mediators include histamine, bradykinin, and prostaglandins.
- Outcome can be resolution, progression to chronic inflammation, or abscess formation.
Chronic Inflammation
Chronic inflammation persists for weeks or years, often occurring when the stimulus for acute inflammation remains or through persistent autoimmune responses. It involves a distinct cellular infiltrate compared to the acute phase and results in more significant tissue destruction.
- Infiltrating cells: Macrophages, lymphocytes, and plasma cells.
- Often characterized by tissue destruction and simultaneous healing attempts via fibrosis.
- Granulomatous inflammation is a specific pattern involving activated macrophages (epitheloid cells).
- Common causes include persistent infections, prolonged exposure to toxic agents, and autoimmunity.
- Angiogenesis and fibrosis are hallmark repair attempts in chronic states.
Wound Healing Phases
Wound healing is a complex biological process consisting of overlapping phases designed to restore tissue integrity. The efficiency of this process is heavily dependent on factors such as nutrition, blood supply, and the presence of underlying systemic diseases like diabetes.
- Hemostasis phase: Platelet aggregation and fibrin clot formation.
- Inflammatory phase: Recruitment of macrophages to clean the wound site.
- Proliferative phase: Formation of granulation tissue and epithelialization.
- Maturation phase: Collagen remodeling and increase in tensile strength.
- Primary intention: Clean incised wounds; secondary intention: Large defects with significant tissue loss.
Fibrosis and Scar Formation
Fibrosis occurs when healing involves the extensive deposition of connective tissue, leading to scar formation rather than complete regeneration of normal tissue. This process is driven by growth factors that stimulate fibroblasts and the excessive production of extracellular matrix components.
- TGF-beta is the most important cytokine for stimulating fibrosis.
- Characterized by dense collagen deposition.
- Can lead to organ dysfunction if scarring is excessive (e.g., liver cirrhosis).
- Keloid formation occurs when there is excessive collagen overgrowth beyond the original wound boundary.
- Distinction between regenerative tissue (functional) and scar tissue (fibrotic).
Exam Tip
Always draw a labeled diagram of the cardinal signs of inflammation and the overlapping phases of wound healing; visual flowcharts are highly valued by examiners.
Common Mistakes
- Confusing the roles of neutrophils in acute inflammation versus macrophages in chronic inflammation.
- Failing to distinguish between regeneration (restoring original architecture) and repair (fibrosis/scarring).
- Ignoring the role of TGF-beta as the primary driver for excessive fibrosis in clinical scenarios.
More Revision Notes
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