(3) Necrosis Explanation: Necrosis is death of body tissue. It occurs when there is not enough blood flowing to the tissue, whether from injury, radiation, or chemicals. Necrosis is riot reversible. When substantial areas of tissue die due to a lack of blood supply, the condition is called gangrene. Necrosis is caused by factors external to the cell or tissue, such as infection, toxins, or trauma that result unregulated digestion of cell components.