Final answer:
Histamine is the most directly responsible agent for the increased capillary permeability during the inflammatory reaction, allowing immune cells and fluids to move to the affected tissue, which leads to swelling and also contributes to redness and warmth by increasing the blood flow to the area.
Step-by-step explanation:
The most directly responsible agent for the increase in capillary permeability during the inflammatory reaction is histamine. During an inflammatory response, tissue injury triggers the release of various chemicals such as cytokines and histamines. Histamine, released from mast cells upon injury or in response to an allergen, plays a crucial role as it causes the endothelial cells of the capillaries to become more permeable.
This increased permeability allows immune cells, like white blood cells, and other substances to leave the bloodstream and move into the affected tissues to facilitate healing. Consequently, this can lead to swelling, or edema, as fluid accumulates in the tissue spaces around the inflamed area. Histamine's role in vasodilation, increasing the diameter of capillaries, is also responsible for the redness and warmth associated with inflammation due to the increased blood flow to the affected area.
The redness of inflammation is attributed to increased blood flow, which is mainly a result of vasodilation caused by various inflammatory mediators including histamine.