Answer:
Mast cells and histamines
Step-by-step explanation:
Mast cells release several chemicals like histamine, cytokines, and other compounds that dilate blood vessels in the affected area. During the inflammatory reaction, mast cells release substances such as histamine. Histamine is a vasodilator and dilates blood vessels and increases their permeability.
The increased permeability of vessels makes the tissue fluid leak from the vessel. The swelling in the area stimulates pain receptors. This is followed by the arrival of neutrophils and monocytes (which become macrophages) through the capillary wall and phagocytosis of pathogens.