1. A necrosis, or death, of tissue or bone, usually resulting from a deficient or absent blood supply to certain body parts, sometimes permitting bacteria to invade them and to accelerate their decay.

The extremities are most often affected, but it can occur in the intestines and gallbladder, too. Internal gangrene may be a complication of strangulated hernia, appendicitis, cholecystitis, or thrombosis of the mesenteric arteries to the intestines.

2. Etymology: gangrene comes from Greek ganggraina, denoting "an eating sore that ends in mortification" or "death" (of the flesh) and subsequently a rotting of the affected parts.

The causes or origins of gangrene

Gangrene is usually caused by obstruction of the blood supply to an organ or tissue, possibly resulting from inflammatory processes, injury, or degenerative changes; such as, arteriosclerosis. Arteriosclerosis is a disease in which thickening, hardening, and the loss of elasticity of the arterial walls result in impaired blood circulation which develops with aging, and in hypertension, diabetes, hyperlipidemia, and other conditions.

It is commonly a sequela, or a secondary consequence or result, of boils, frostbite, crushing injuries, or diseases; such as, diabetes mellitus (severe, chronic form of diabetes) and Raynaud's disease (a circulatory disorder caused by insufficient blood supply to the hands and feet and resulting in cyanosis, numbness, pain, and, in extreme cases, gangrene).

The part of the body that dies from gangrene is known as a slough (for soft tissues) or a sequestrum (for bone). The dead matter must be removed before healing can take place.

Extensive destruction of the skin surrounding a draining wound, following removal of an amebic abscess of the liver.

The death of tissue due to vascular insufficiency without bacterial invasion.

The tissue simply dries up and shrivels.

The invasion of a deep penetrating wound (in which the blood supply is compromised) by anaerobic bacteria (bacteria that can survive with little or no oxygen); such as, members of the Clostridium family of bacteria.

The bacteria generate gas and pus. Gas gangrene is an acute, painful, dangerous condition.

A chronic ulcer that appears in pressure areas in debilitated sufferers confined to bed or otherwise immobilized, because of a circulatory defect from the enhanced tissue pressure in high-contact areas, often occurring over a bony prominence: Nosocomial gangrene often results in hospitals when an invalid is in a reclining position for a long period of time.