User:Kogledom

Thermoregulation in humans
Humans have been able to adapt to a great diversity of climates, including hot humid and hot arid. High temperatures pose serious stresses for the human body, placing it in great danger of injury or even death. In order to deal with these climatic conditions, humans have developed physiologic and cultural modes of adaptation.

The temperature of the body is regulated almost entirely by nervous feedback mechanisms, and almost all these operate through temperature-regulating centers located in the hypothalamus. For these feedback mechanisms to operate, there must also be temperature detectors to determine when the body temperature bocome either too hight or too low.

Information about the external temperature is provided by thermoreceptors in the skin (and probably other organs, such as muscle). Internal temperature is monitored by central thermoreceptive neurons in the anterior hypolathamus. The central thermoreceptors monitor the temperature of the blood. The system acts as a servomechanism (a control system that uses negative feedback to operate another system) with a setpoint at the normal body temperature. Error signals, which represent a deviation form the set point, evoke responses that tend to restore body temperature toward set point. These responses are mediated by the autonomic, somatic and endocrine systems.

Temperature-decreasing mechanisms when the body is too hot The temperature control system uses three important mechanisms to reduce body heat when the body temperature becmes too great:
 * 1) Vasodilatation of skin blood vessels. In almost all areas of the body, the skin blood vessels become intensely dilated. This is caused by inhibition of the sympathetic centers in the posterior hypothalamus taht cause vasoconstriction. Full vasodilatation can increase the rate of heat transfer to the skin as much as eightfold.
 * 2) Sweating. The rate of evaporative heat loss resulting from sweating sharply increases when the body core tekmperature rises above the set point. An additional 1°C increase in body temperature causes enough sweating to remove 10 times the basal rate of body heat production.
 * 3) Decrease in heat production. The mechanisms that cause excess heat production, such as shivering and chemical thermogenesis, are strongly inhibited.

Temperature-increasing mechanisms when the body is too cold When the body is too cold, the temperature control system institutes exacly opposite procedures. They are:
 * 1) Skin vasoconstriction throught the body. This is caused by stimulation of the posterior hypothalamic sympathetic centers.
 * 2) Increase in thermogenesis (heat production). Heat production by the methabolic systems is increased by promoting shivering (during maximum shivering, body heat production can rise to four to five times normal), sympathetic excitation of heat production (chemical thermogenesis in brown fat in infants and ability of norepinephrine and epinephrine to uncouple oxidative phosphorylation) and tyroxine secretion (this increase in methabolism does not occur immediately but requires several weeks' expositure to cold to make the tyroid gland hypertrophy and reach its new level of tyrixine secretion, making it important in adaptation to cold).