Thermoregulation 4, Heat gain and loss mechanisms

This situation initiates body warming mechanisms. Some mechanisms conserve heat which is already in the body while others work by increasing heat production using thermogenesis. This literally means ‘the beginning of heat’ and describes any process in which heat is produced.In order to preserve heat in the physiologically essential core organs, blood supply to the cold peripheries such as hands and feet is reduced. Arterial supply of blood is restricted by reduction of arterial lumens. This is why we get cold hands and feet in cold environments. In humans, reduction of arterial blood supply to cold extremities is a very efficient mechanism. Reduction in blood perfusion can be so pronounced that the temperature in extremities may drop to 0oC. When this happens the tissue freezes. As a tissue freezes, ice crystals form in the cytosol of the cells. The expansion of these crystals results in rupture of cell membranes, disrupting tissue integrity at the cellular level. Tissue necrosis (necrosis means death) caused by this freezing mechanism is called frost bite and often necessitates amputations. Interestingly this same process of tissue destruction on freezing explains why people who are frozen after death, in the hope of being brought back to life in the future, never will be.