What physiological change causes the extravascular accumulation of fluid after a bee sting?

• A. Demargination of leukocytes
• B. Vasoconstriction
• C. Gap formation between endothelial cells
• D. Dilation of blood vessels

Answer: (C)

The extravascular accumulation of fluid following a bee sting is primarily attributed to gap formation between endothelial cells. When a bee sting occurs, it triggers an inflammatory response mediated by various chemical signals, including histamine and other inflammatory mediators released from mast cells and damaged tissues. These molecules lead to increased permeability of blood vessels, allowing plasma and proteins to leak out into the surrounding tissues.

The phenomenon of gap formation refers to the loosening of tight junctions between endothelial cells in the capillary walls. This loosening results in the widening of spaces between the cells, facilitating the movement of fluid and solutes from the intravascular space to the extravascular space, ultimately leading to localized swelling and edema. Therefore, the accumulation of fluid in the tissues following a bee sting is a direct result of this increased permeability caused by the inflammatory response.

In contrast, other physiological changes such as vasoconstriction or dilation of blood vessels affect blood flow and pressure but do not directly promote the extravascular accumulation of fluid in the same manner. Vasoconstriction would limit blood flow and fluid accumulation, whereas dilation, while potentially increasing blood flow, is the initial response that precedes the permeability changes. Demargination of leukocytes refers to the movement of