Which vessels are leaky in the inflammatory response?

• A. Arterioles
• B. Capillaries
• C. Venules
• D. Post capillary venules

Answer: (D)

During inflammation, mediators such as histamine cause endothelial cells to contract, creating gaps in the vessel walls and allowing fluid, proteins, and leukocytes to pass into the tissue. The most pronounced permeability changes occur in the post-capillary venules, whose endothelium is looser and more readily forms gaps, making them the main route for edema formation and leukocyte extravasation. Arterioles mainly dilate to produce redness and warmth and are less involved in protein-rich leakage, while capillaries do leak but not to the extent and with the same ease of leukocyte passage as post-capillary venules. So, the vessels that are leaky in the inflammatory response are the post-capillary venules.