<P> As in other mammals, thermoregulation in humans is an important aspect of homeostasis . In thermoregulation, body heat is generated mostly in the deep organs, especially the liver, brain, and heart, and in contraction of skeletal muscles . Humans have been able to adapt to a great diversity of climates, including hot humid and hot arid . High temperatures pose serious stress for the human body, placing it in great danger of injury or even death . For humans, adaptation to varying climatic conditions includes both physiological mechanisms resulting from evolution and behavioural mechanisms resulting from conscious cultural adaptations . </P> <P> There are four avenues of heat loss: convection, conduction, radiation, and evaporation . If skin temperature is greater than that of the surroundings, the body can lose heat by radiation and conduction . But, if the temperature of the surroundings is greater than that of the skin, the body actually gains heat by radiation and conduction . In such conditions, the only means by which the body can rid itself of heat is by evaporation . So, when the surrounding temperature is higher than the skin temperature, anything that prevents adequate evaporation will cause the internal body temperature to rise . During sports activities, evaporation becomes the main avenue of heat loss . Humidity affects thermoregulation by limiting sweat evaporation and thus heat loss . </P> <P> The core temperature of a human is regulated and stabilized primarily by the hypothalamus: a region of the brain linking the endocrine system to the nervous system, and more specifically by the anterior hypothalamic nucleus and the adjacent preoptic area regions of the hypothalamus . As core temperature varies from the set point, endocrine production initiates control mechanisms to increase or decrease energy production / dissipation as needed to return the temperature toward the set point (see figure). </P> <Ul> <Li> Eccrine sweat glands under the skin secrete sweat (a fluid containing mostly water with some dissolved ions), which travels up the sweat duct, through the sweat pore and onto the surface of the skin . This causes heat loss via evaporative cooling; however, a lot of essential water is lost . </Li> <Li> The hair on the skin lie flat, preventing heat from being trapped by the layer of still air between the hair . This is caused by tiny muscles under the surface of the skin called arrector pili muscles relaxing so that their attached hair follicles are not erect . These flat hairs increase the flow of air next to the skin increasing heat loss by convection . When environmental temperature is above core body temperature, sweating is the only physiological way for humans to lose heat . </Li> <Li> Arteriolar vasodilation occurs . The smooth muscle walls of the arterioles relax allowing increased blood flow through the artery . This redirects blood into the superficial capillaries in the skin increasing heat loss by convection and conduction . </Li> </Ul>

Which part of the human body regulates temperature