A patient receives intradermal histamine during a skin test. Within minutes, venules at the injection site show gaps between endothelial cells with leakage of protein-rich fluid. Which mechanism explains this pattern of increased vascular permeability?
- A Retraction of endothelial cells opening intercellular gaps ✓
- B Direct endothelial injury causing necrosis
- C Leakage from newly formed capillaries during repair
- D Increased transcytosis across intact endothelium
Correct answer: A. Retraction of endothelial cells opening intercellular gaps
Explanation
Histamine, bradykinin and leukotrienes cause immediate transient leakage by triggering contraction of venular endothelial cells after binding to receptors, opening reversible intercellular gaps. Direct injury produces delayed prolonged leakage over hours to days, and leakiness of newly formed vessels occurs only during tissue repair. The venule, not the capillary, is the main site of this response.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.