Which factor causes capillaries to become more permeable during the congestion phase of inflammation?

The correct response is based on the role of histamine in the inflammatory process. During the congestion phase of inflammation, histamine, which is released primarily by mast cells and basophils, acts as a potent vasodilator and increases the permeability of the capillaries. This allows for easier passage of fluids, proteins, and immune cells out of the blood vessels and into the affected tissue, facilitating the inflammatory response.

Histamine achieves this by causing the endothelial cells lining the capillaries to retract slightly, creating interendothelial gaps that increase vascular permeability. This is crucial because it contributes to the accumulation of inflammatory cells and plasma proteins at the site of injury or infection, which are necessary for effective healing and immune defense.

Other factors like cytokines, platelet activation, and increased blood flow do play roles in inflammation and might influence vascular dynamics, but it is specifically the action of histamine that directly results in increased capillary permeability during this initial phase.