Body temperature is kept constant by balancing both heat gain and heat loss. Humans need to maintain a constant body temperature of about 37°C. To maintain this temperature at a constant point throughout the body’s internal systems, mechanisms must be in place to accurately measure present body temperature, and to regulate as needed. This system is known as the thermo-regulatory system. The metabolic heat generated by oxidation of food in the visceral organs and tissues (body core) is a constant source of heat. Core body temperature can also be dramatically increased with muscular activity, nervous and hormonal factors (such as sympathetic nervous activity), catecholamines, and thyroid hormones.
Body temperature can vary in different regions. The tissues of the extremities and the skin are far from the core (the core consists of the brain and visceral organs and tissues in the trunk), and they are in direct contact with the external environment. These tissues tend to have slightly lower temperatures.