Inflammatory response

Any injury, cut or graze allows microbes and other foreign material to enter the body. A blood clot rapidly seal the wound. 

Inflammation at the site -inflammatory responses- destroy invading microbes. Damaged white blood cells and mast cells found in the connective tissue below the skin and around blood vessels release special chemicals e.g histamine.

Chemicals cause the arterioles in the area to dilate which increases blood flow in the capillaries of the infected site.

Histamines also increase permeability of the capillaries: cells in the capillary walls seperate slightly so the vessels leak. Plasma fluid, white blood cells and antibodies leak from the blood into the tissue causing oedema (swelling). Infecting microbes can now be attacked by these intact white cells.