Histamine mediates the immediate transient increase in vascular permeability of acute inflammation. This response occurs primarily at which site, and by what mechanism?
- A Arterioles, by endothelial cell contraction
- B Capillaries, by direct endothelial injury
- C Postcapillary venules, by endothelial cell contraction ✓
- D Postcapillary venules, by leukocyte-mediated endothelial damage
Correct answer: C. Postcapillary venules, by endothelial cell contraction
Explanation
Histamine, bradykinin and leukotrienes bind to endothelial receptors causing reversible actin-myosin contraction, opening intercellular gaps. This immediate transient response is confined to postcapillary venules, which are 20 to 60 micrometers in diameter. Arterioles and capillaries do not respond this way, direct endothelial injury produces a delayed prolonged leak across all vessel levels, and leukocyte-mediated damage occurs late after adhesion, not immediately.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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