Acute Inflammation MCQ — NEET PG Practice Question | NEETPGAI
Acute Inflammation
medium
microscope Pathology
Which of the following is the primary mechanism by which histamine causes increased vascular permeability in acute inflammation?
A. Contraction of endothelial cells leading to intercellular gap formation
B. Direct endothelial cell necrosis
C. Degradation of basement membrane collagen
D. Inhibition of tight junction protein synthesis
Explanation
Mechanism of Histamine-Induced Increased Permeability
Key Point
Histamine causes acute inflammatory edema by inducing endothelial cell contraction, not cell death. This contraction creates intercellular gaps in post-capillary venules, allowing fluid and plasma proteins to escape into the interstitium.
Cellular Mechanism
Histamine binds to H1 and H2 receptors on endothelial cells, triggering:
1.
Increased intracellular calcium (Ca²⁺)
2.
Activation of myosin light-chain kinase (MLCK)
3.
Contraction of the endothelial cell cytoskeleton
4.
Widening of intercellular junctions
Timeline and Characteristics
High-YieldNEET PG
Histamine-induced permeability is:
Immediate onset (within seconds to minutes)
Transient (resolves within 15–30 minutes)
Reversible (no cell death occurs)
Occurs primarily in post-capillary venules (not arterioles or capillaries)
Comparison with Other Mediators
Table
Mediator
Mechanism
Onset
Duration
Site
Histamine
Endothelial contraction
Immediate
15–30 min
Post-capillary venules
Bradykinin
Endothelial contraction + direct effect
Immediate
15–30 min
Post-capillary venules
Leukotrienes (LTC₄, LTD₄, LTE₄)
Endothelial contraction
Immediate
Prolonged
Post-capillary venules
TNF-α, IL-1
Endothelial injury + leukocyte adhesion
Delayed
Hours
Multiple sites
Complement (C3a, C5a)
Endothelial contraction + leukocyte activation
Immediate
Variable
Post-capillary venules
Clinical Pearl
Antihistamines (H1 blockers) are effective in histamine-mediated acute inflammation but ineffective against bradykinin, leukotrienes, or complement-mediated permeability — explaining why they work well in allergic reactions but not in severe inflammatory conditions.
Warning
Do not confuse histamine-induced permeability (reversible contraction) with severe inflammatory mediators (TNF-α, IL-1) that cause endothelial injury and prolonged leakage.
Robbins 10e Ch 2
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