Answer
The thermostat of the body is the preoptic nucleus (PON) of the hypothalamus. It receives thermogenic stimuli from the skin and blood and these enable it to monitor and regulate body temperature. The PON responds by signalling the anterior nucleus heat loss center or the posterior nucleus heat promoting center and by these negative feedback signals modulate the changes in body temperature.
The body has a temperatures set point. When the preoptic nucleus senses a too high temperature it activates the anterior heat loss center in a negative feedback process. This has the following effects: cutaneous blood vessels dilate, and blood flow to the periphery increases. As a consequence, heat loss at the skin surface is enhanced; if it is necessary to enhance this initial effect, sweating is triggered, and more heat is lost as the sweat evaporates. Another effect of this feedback mechanism is to suppress activity of the hypothalamic heat promoting center.
Work Step by Step
When the body's temperature situation is reversed and the thermostat detects too low body temperature, a different mechanism comes into play. The sympathetic nerves of the blood vessels are stimulated by the hypothalamus and this cause vasoconstriction of peripheral blood vessels. One consequence of this action is that most of the blood is retained in the deep core organs; as a result heat loss from the periphery is decreased. If this mechanism does maintain a warm enough temperature, the body employs the active process of thermogenic shivering. This shivering heat-generating activity involves the alternating contraction of pairs of muscle antagonists. These muscle contractions release heat from ATP, and have the ability to raise the rate of heat production several-fold.
