What effect do the mediators released by activated mast cells have on blood vessels?

Activated mast cells play an essential role in the immune response, particularly during allergic reactions and inflammation. When mast cells are activated, they release various mediators, including histamine, cytokines, and other inflammatory substances.

Histamine, one of the primary mediators released by mast cells, has a significant effect on blood vessels. It causes vasodilation, which is the widening of blood vessels, leading to increased blood flow to the affected area. This increased blood flow can result in redness and warmth in tissues affected by an inflammatory response.

In addition to vasodilation, these mediators also increase the permeability of the blood vessel walls. Increased permeability allows for proteins and fluid to escape from the bloodstream into the surrounding tissues, leading to swelling (edema) and providing immune cells access to inflammatory sites. This process is crucial for the effective functioning of the immune system as it facilitates the movement of leukocytes and nutrients to the site of injury or infection.

Therefore, the correct response reflects the dual action of mediators released by activated mast cells: they cause both vasodilation and increased permeability of blood vessels, contributing to the classic signs of inflammation—redness, heat, swelling, and pain.