Within minutes of a mosquito bite, plasma protein-rich fluid escapes from the microcirculation into the surrounding tissue. Which mechanism accounts for this immediate increase in vascular permeability?

• A Leukocyte-mediated endothelial injury in arterioles
• B Direct necrosis of capillary endothelium
• C Contraction of endothelial cells lining postcapillary venules ✓
• D Increased transcytosis through enlarged venular caveolae

Explanation

Histamine, bradykinin and leukotrienes bind receptors on postcapillary venular endothelium and trigger rapid reversible contraction, opening intercellular gaps. This immediate transient response peaks within minutes and lasts 15 to 30 minutes. Direct endothelial injury causes a delayed prolonged leak that begins after several hours, as in sunburn, so option B describes a different pattern. Leukocyte injury affects venules, capillaries and arterioles during later stages.

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.