During the inflammation phase, which vascular change occurs due to histamines?

• A. Vasoconstriction and decreased permeability
• B. Vasodilation and increased capillary permeability
• C. No effect
• D. Increased clotting

Answer: (B)

The main idea is how histamine changes blood vessels during inflammation. Histamine released by mast cells and basophils makes blood vessels dilate (vasodilation) and increases the permeability of capillaries. This means more blood flows to the injured area and the vessels become leakier, allowing fluid and proteins to exit into the tissue. The combination of enhanced flow and leakage leads to redness, warmth, and swelling, and it helps immune cells reach the site of injury.

Vasoconstriction or no effect would not explain the typical inflammatory signs produced by histamine, and increased clotting is not the direct vascular change histamine drives in acute inflammation.