Thermoregulation is a homeostatic process that keeps the body temperature within acceptable limits required for the complex of biochemical systems in the body. The human body undergoes internal and external changes in temperature. Examples of heating factors are the constant basal metabolism, exercise, environmental high temperatures, and solar radiation. Cold factors involve e.g. lower basal metabolism due to fasting and low environmental temperatures.
Heat exchange with the environment occurs via four processes:
- Radiation - a mechanism by which warm objects lose energy (e.g. sun)
- Conduction - direct energy transfer through physical contact
- Convection - energy transfer to air
- Evaporation - transfer from a liquid to vapor
The process of thermoregulation is controlled by neuronal (temperature sensors, hypothalamic centres, brain, spinal cord, and muscles) and endocrine tissues (adrenal gland, liver, thyroid gland, pituitary and brown fat). The input of information about temperature from the cold and heat sensors (receptors) enters the anterior hypothalamus (sensor). The actual coordination of thermoregulation occurs in the posterior hypothalamus (actuator). The latter regulates the reaction of the body towards changes in temperature. A cold stimulus causes a reaction that increases the heat production and reduces the heat loss, while heat production is reduced and heat loss is stimulated when temperatures increase.
Water is a good conductor of heat.
Conduction is the process of heat loss to air that overlies the surface of the body.
Evaporation at rest accounts for 20% of the average heat loss.
Evaporation requires energy.