Answer:
Frostbite is a more severe and more common form of cold injury that essentially consists of local freezing of tissues. The injury has two components - the initial freeze injury and a reperfusion injury occurring during rewarming. The initial response to tissue cooling is vasoconstriction and arteriovenous shunting, intermittently relieved (every 5-7 minutes) by vasodilatation, the so-called hunting response. With prolonged exposure, this response fails, and the temperature of freezing tissue approximates ambient temperature until -2 degrees Celsius. At this point extracellular ice crystals form, and as they enlarge, the osmotic pressure of the interstitium increases resulting in the movement of intracellular water into the interstitium. Cells shrink and become hyperosmolar, disrupting cellular enzyme function. If freezing is rapid, intracellular ice crystals form resulting in immediate cell death. Intravascular disruption of endothelial cells and red cell sludging result in cessation of circulation. (Taken directly from Greenfield, Surgery: Principles and Practice).